.NET provides the following two standard patterns for performing I/O-bound and compute-bound asynchronous operations:
Asynchronous Programming Model (APM), in which asynchronous operations are represented by a pair of begin/end methods. For example: System.IO.FileStream.BeginRead and System.IO.Stream.EndRead.
Event-based asynchronous pattern (EAP), in which asynchronous operations are represented by a method/event pair that are named
<OperationName>Asyncand<OperationName>Completed. For example: System.Net.WebClient.DownloadStringAsync and System.Net.WebClient.DownloadStringCompleted.
The Task Parallel Library (TPL) can be used in various ways in conjunction with either of the asynchronous patterns. You can expose both APM and EAP operations as Task objects to library consumers, or you can expose the APM patterns but use Task objects to implement them internally. In both scenarios, by using Task objects, you can simplify the code and take advantage of the following useful functionality:
Register callbacks, in the form of task continuations, at any time after the task has started.
Coordinate multiple operations that execute in response to a
Begin_method by using the System.Threading.Tasks.TaskFactory.ContinueWhenAll and System.Threading.Tasks.TaskFactory.ContinueWhenAny methods, or the System.Threading.Tasks.Task.WaitAll and System.Threading.Tasks.Task.WaitAny methods.Encapsulate asynchronous I/O-bound and compute-bound operations in the same
Taskobject.Monitor the status of the
Taskobject.Marshal the status of an operation to a
Taskobject by using System.Threading.Tasks.TaskCompletionSource.
Wrap APM operations in a Task
Both the System.Threading.Tasks.TaskFactory and System.Threading.Tasks.TaskFactory classes provide several overloads of the System.Threading.Tasks.TaskFactory.FromAsync and System.Threading.Tasks.TaskFactory.FromAsync methods that let you encapsulate an APM begin/end method pair in one System.Threading.Tasks.Task or System.Threading.Tasks.Task instance. The various overloads accommodate any begin/end method pair that have from zero to three input parameters.
For pairs that have End methods that return a value (a Function in Visual Basic), use the methods in System.Threading.Tasks.TaskFactory that create a System.Threading.Tasks.Task. For End methods that return void (a Sub in Visual Basic), use the methods in System.Threading.Tasks.TaskFactory that create a System.Threading.Tasks.Task.
For those few cases in which the Begin method has more than three parameters or contains ref or out parameters, additional FromAsync overloads that encapsulate only the End method are provided.
The following example shows the signature for the FromAsync overload that matches the System.IO.FileStream.BeginRead and System.IO.FileStream.EndRead methods.
sample · csharpsamples/snippets/csharp/VS_Snippets_Misc/fromasync/cs/fromasync.cs01
using System;
using System.Collections.Concurrent;
using System.Collections.Generic;
using System.Diagnostics;
using System.IO;
using System.Linq;
using System.Text;
using System.Threading;
using System.Threading.Tasks;
using System.Net;
namespace specialNamespaceForOneMethodSignature
{
using System;
class Task<TResult>
{
public TResult TValue;
}
class Dummy <TResult>
{
// <snippet01>
public Task<TResult> FromAsync<TArg1, TArg2, TArg3>(
Func<TArg1, TArg2, TArg3, AsyncCallback, object, IAsyncResult> beginMethod, //BeginRead
Func<IAsyncResult, TResult> endMethod, //EndRead
TArg1 arg1, // the byte[] buffer
TArg2 arg2, // the offset in arg1 at which to start writing data
TArg3 arg3, // the maximum number of bytes to read
object state // optional state information
)
//</snippet01>
{ return new Task<TResult>(); }
}
}
namespace APM_Task
{
class TestFileStreamNaive
{
//<snippet02>
public string GetFileData(string path)
{
FileInfo fi = new FileInfo(path);
byte[] data = new byte[fi.Length];
FileStream fs;
// a using statement is ok here because we Wait before returning
// and will be done with the filestream.
using (fs = new FileStream(path, FileMode.Open, FileAccess.Read, FileShare.Read, data.Length, true))
{
//Task<int> returns the number of bytes read
Task<int> task = Task<int>.Factory.FromAsync(
fs.BeginRead, fs.EndRead, data, 0, data.Length, null);
task.Wait();
return new UTF8Encoding().GetString(data);
}
}
//</snippet02>
static void Main()
{
TestFileStreamNaive instance = new TestFileStreamNaive();
string s = instance.GetFileData("testfile.txt");
}
}
class AsyncResult : IAsyncResult
{
public AsyncResult() { }
public object AsyncState
{
get { return "Hello from a parallel universe."; }
}
public WaitHandle AsyncWaitHandle
{
get { throw new NotImplementedException(); }
}
public bool CompletedSynchronously
{
get { throw new NotImplementedException(); }
}
public bool IsCompleted
{
get { throw new NotImplementedException(); }
}
static IAsyncResult DoSomethingAsynchronously()
{
return new AsyncResult();
}
//<snippet07>
static Task<String> ReturnTaskFromAsyncResult()
{
IAsyncResult ar = DoSomethingAsynchronously();
Task<String> t = Task<string>.Factory.FromAsync(ar, _ =>
{
return (string)ar.AsyncState;
});
return t;
}
//</snippet07>
}
//<snippet08>
class WebDataDownloader
{
static void Main()
{
WebDataDownloader downloader = new WebDataDownloader();
string[] addresses = { "http://www.msnbc.com", "http://www.yahoo.com",
"http://www.nytimes.com", "http://www.washingtonpost.com",
"http://www.latimes.com", "http://www.newsday.com" };
CancellationTokenSource cts = new CancellationTokenSource();
// Create a UI thread from which to cancel the entire operation
Task.Factory.StartNew(() =>
{
Console.WriteLine("Press c to cancel");
if (Console.ReadKey().KeyChar == 'c')
cts.Cancel();
});
// Using a neutral search term that is sure to get some hits.
Task<string[]> webTask = downloader.GetWordCounts(addresses, "the", cts.Token);
// Do some other work here unless the method has already completed.
if (!webTask.IsCompleted)
{
// Simulate some work.
Thread.SpinWait(5000000);
}
string[] results = null;
try
{
results = webTask.Result;
}
catch (AggregateException e)
{
foreach (var ex in e.InnerExceptions)
{
OperationCanceledException oce = ex as OperationCanceledException;
if (oce != null)
{
if (oce.CancellationToken == cts.Token)
{
Console.WriteLine("Operation canceled by user.");
}
}
else
{
Console.WriteLine(ex.Message);
}
}
}
finally
{
cts.Dispose();
}
if (results != null)
{
foreach (var item in results)
Console.WriteLine(item);
}
Console.ReadKey();
}
Task<string[]> GetWordCounts(string[] urls, string name, CancellationToken token)
{
TaskCompletionSource<string[]> tcs = new TaskCompletionSource<string[]>();
WebClient[] webClients = new WebClient[urls.Length];
// If the user cancels the CancellationToken, then we can use the
// WebClient's ability to cancel its own async operations.
token.Register(() =>
{
foreach (var wc in webClients)
{
if (wc != null)
wc.CancelAsync();
}
});
object m_lock = new object();
int count = 0;
List<string> results = new List<string>();
for (int i = 0; i < urls.Length; i++)
{
webClients[i] = new WebClient();
#region callback
// Specify the callback for the DownloadStringCompleted
// event that will be raised by this WebClient instance.
webClients[i].DownloadStringCompleted += (obj, args) =>
{
if (args.Cancelled == true)
{
tcs.TrySetCanceled();
return;
}
else if (args.Error != null)
{
// Pass through to the underlying Task
// any exceptions thrown by the WebClient
// during the asynchronous operation.
tcs.TrySetException(args.Error);
return;
}
else
{
// Split the string into an array of words,
// then count the number of elements that match
// the search term.
string[] words = null;
words = args.Result.Split(' ');
string NAME = name.ToUpper();
int nameCount = (from word in words.AsParallel()
where word.ToUpper().Contains(NAME)
select word)
.Count();
// Associate the results with the url, and add new string to the array that
// the underlying Task object will return in its Result property.
results.Add(String.Format("{0} has {1} instances of {2}", args.UserState, nameCount, name));
}
// If this is the last async operation to complete,
// then set the Result property on the underlying Task.
lock (m_lock)
{
count++;
if (count == urls.Length)
{
tcs.TrySetResult(results.ToArray());
}
}
};
#endregion
// Call DownloadStringAsync for each URL.
Uri address = null;
try
{
address = new Uri(urls[i]);
// Pass the address, and also use it for the userToken
// to identify the page when the delegate is invoked.
webClients[i].DownloadStringAsync(address, address);
}
catch (UriFormatException ex)
{
// Abandon the entire operation if one url is malformed.
// Other actions are possible here.
tcs.TrySetException(ex);
return tcs.Task;
}
}
// Return the underlying Task. The client code
// waits on the Result property, and handles exceptions
// in the try-catch block there.
return tcs.Task;
}
//</snippet08>
}
#region snippet09
class Calculator
{
public IAsyncResult BeginCalculate(int decimalPlaces, AsyncCallback ac, object state)
{
Console.WriteLine($"Calling BeginCalculate on thread {Thread.CurrentThread.ManagedThreadId}");
Task<string> f = Task<string>.Factory.StartNew(_ => Compute(decimalPlaces), state);
if (ac != null) f.ContinueWith((res) => ac(f));
return f;
}
public string Compute(int numPlaces)
{
Console.WriteLine($"Calling compute on thread {Thread.CurrentThread.ManagedThreadId}");
// Simulating some heavy work.
Thread.SpinWait(500000000);
// Actual implementation left as exercise for the reader.
// Several examples are available on the Web.
return "3.14159265358979323846264338327950288";
}
public string EndCalculate(IAsyncResult ar)
{
Console.WriteLine($"Calling EndCalculate on thread {Thread.CurrentThread.ManagedThreadId}");
return ((Task<string>)ar).Result;
}
}
public class CalculatorClient
{
static int decimalPlaces = 12;
public static void Main()
{
Calculator calc = new Calculator();
int places = 35;
AsyncCallback callBack = new AsyncCallback(PrintResult);
IAsyncResult ar = calc.BeginCalculate(places, callBack, calc);
// Do some work on this thread while the calculator is busy.
Console.WriteLine("Working...");
Thread.SpinWait(500000);
Console.ReadLine();
}
public static void PrintResult(IAsyncResult result)
{
Calculator c = (Calculator)result.AsyncState;
string piString = c.EndCalculate(result);
Console.WriteLine($"Calling PrintResult on thread {Thread.CurrentThread.ManagedThreadId}; result = {piString}");
}
}
#endregion
} //end APM_Task namespace
class FileStreamDemo
{
static void Main()
{
FileStreamDemo fsd = new FileStreamDemo();
// var task = fsd.GetMultiFileData(new string[1]);
fsd.ShowCallingFromAsync();
// fsd.ShowCallingFromAsyncFileData();
// fsd.ProcessFilesAsync();
// task.Wait();
// Console.WriteLine(task.Result);
Console.WriteLine("press any key");
Console.ReadLine();
}
//<snippet03>
const int MAX_FILE_SIZE = 14000000;
public static Task<string> GetFileStringAsync(string path)
{
FileInfo fi = new FileInfo(path);
byte[] data = null;
data = new byte[fi.Length];
FileStream fs = new FileStream(path, FileMode.Open, FileAccess.Read, FileShare.Read, data.Length, true);
//Task<int> returns the number of bytes read
Task<int> task = Task<int>.Factory.FromAsync(
fs.BeginRead, fs.EndRead, data, 0, data.Length, null);
// It is possible to do other work here while waiting
// for the antecedent task to complete.
// ...
// Add the continuation, which returns a Task<string>.
return task.ContinueWith((antecedent) =>
{
fs.Close();
// Result = "number of bytes read" (if we need it.)
if (antecedent.Result < 100)
{
return "Data is too small to bother with.";
}
else
{
// If we did not receive the entire file, the end of the
// data buffer will contain garbage.
if (antecedent.Result < data.Length)
Array.Resize(ref data, antecedent.Result);
// Will be returned in the Result property of the Task<string>
// at some future point after the asynchronous file I/O operation completes.
return new UTF8Encoding().GetString(data);
}
});
}
//</snippet03>
void ShowCallingFromAsync()
{
string path = @"\\docbuild2\public\Main\Logs\DllDiffReport\DllDiffReport_BetweenInBuildAndInProduct.html";
//<snippet04>
Task<string> t = GetFileStringAsync(path);
// Do some other work:
// ...
try
{
Console.WriteLine(t.Result.Substring(0, 500));
}
catch (AggregateException ae)
{
Console.WriteLine(ae.InnerException.Message);
}
//</snippet04>
Console.ReadLine();
}
//not used???
//<snippet12>
public static Task<int> GetFileDataAsync(string path, ref byte[] data)
{
// Error handling omitted for brevity...
FileInfo fi = new FileInfo(path);
data = new byte[fi.Length];
FileStream fs = new FileStream(path, FileMode.Open, FileAccess.Read, FileShare.Read, data.Length, true);
// Task<int> returns the number of bytes read
// Pass FileStream in AsyncState parameter in order to close it from the call site.
return Task<int>.Factory.FromAsync(
fs.BeginRead, fs.EndRead, data, 0, data.Length, fs);
}
//</snippet12>
void ShowCallingFromAsyncFileData()
{
//<snippet13>
string path = @"\\remoteComputer\filename.txt";
byte[] buffer = null;
Task<int> t = GetFileDataAsync(path, ref buffer);
// Can do some other work here:
// ...
for(int i = 0; i < 10; i++)
Console.Write("Working... ");
var result =
t.ContinueWith((antecedent) =>
{
// Error handling omitted...
return new UTF8Encoding().GetString(buffer);
});
// Can also do some other work here:
// ...
for (int i = 0; i < 10; i++)
Console.Write("Working more... ");
try
{
t.Wait();
Console.WriteLine(result.Result.Substring(0, 50));
}
catch (AggregateException ae)
{
Console.WriteLine(ae.InnerException.Message);
}
//</snippet13>
Console.ReadLine();
}
// nested dummy class for snippet0 5 below
class MyCustomState
{
public string StateData { get; set; }
public MyCustomState() { StateData = "Hello"; }
}
private MyCustomState GetCustomState()
{
return new MyCustomState();
}
//<snippet05>
public Task<string> GetFileStringAsync2(string path)
{
FileInfo fi = new FileInfo(path);
byte[] data = new byte[fi.Length];
MyCustomState state = GetCustomState();
FileStream fs = new FileStream(path, FileMode.Open, FileAccess.Read, FileShare.Read, data.Length, true);
// We still pass null for the last parameter because
// the state variable is visible to the continuation delegate.
Task<int> task = Task<int>.Factory.FromAsync(
fs.BeginRead, fs.EndRead, data, 0, data.Length, null);
return task.ContinueWith((antecedent) =>
{
// It is safe to close the filestream now.
fs.Close();
// Capture custom state data directly in the user delegate.
// No need to pass it through the FromAsync method.
if (state.StateData.Contains("New York, New York"))
{
return "Start spreading the news!";
}
else
{
// If we did not receive the entire file, the end of the
// data buffer will contain garbage.
if (antecedent.Result < data.Length)
Array.Resize(ref data, antecedent.Result);
// Will be returned in the Result property of the Task<string>
// at some future point after the asynchronous file I/O operation completes.
return new UTF8Encoding().GetString(data);
}
});
}
//</snippet05>
string[] GetFilesToRead()
{
return new string[3] { "test.txt", "test1.txt", "test2.txt" };
}
//<snippet06>
public Task<string> GetMultiFileData(string[] filesToRead)
{
FileStream fs;
Task<string>[] tasks = new Task<string>[filesToRead.Length];
byte[] fileData = null;
for (int i = 0; i < filesToRead.Length; i++)
{
fileData = new byte[0x1000];
fs = new FileStream(filesToRead[i], FileMode.Open, FileAccess.Read, FileShare.Read, fileData.Length, true);
// By adding the continuation here, the
// Result of each task will be a string.
tasks[i] = Task<int>.Factory.FromAsync(
fs.BeginRead, fs.EndRead, fileData, 0, fileData.Length, null)
.ContinueWith((antecedent) =>
{
fs.Close();
// If we did not receive the entire file, the end of the
// data buffer will contain garbage.
if (antecedent.Result < fileData.Length)
Array.Resize(ref fileData, antecedent.Result);
// Will be returned in the Result property of the Task<string>
// at some future point after the asynchronous file I/O operation completes.
return new UTF8Encoding().GetString(fileData);
});
}
// Wait for all tasks to complete.
return Task<string>.Factory.ContinueWhenAll(tasks, (data) =>
{
// Propagate all exceptions and mark all faulted tasks as observed.
Task.WaitAll(data);
// Combine the results from all tasks.
StringBuilder sb = new StringBuilder();
foreach (var t in data)
{
sb.Append(t.Result);
}
// Final result to be returned eventually on the calling thread.
return sb.ToString();
});
}
//</snippet06>
public string ProcessData(Task[] arr)
{
return "processed";
}
//<snippet11>
void ProcessFilesAsync()
{
string[] files = Directory.GetFiles(@"\\remoteComputer\folderName\", "*.*", SearchOption.AllDirectories);
CancellationTokenSource cts = new CancellationTokenSource();
List<Task<string>> tasks = new List<Task<string>>();
foreach (var file in files)
{
Task<string> t = null;
try
{
t = GetFileStringAsync3(file, cts.Token);
}
catch
{
Console.WriteLine($"Argument exception on {file}");
continue;
}
t.ContinueWith((antecedent) => ProcessFileData(antecedent.Result));
tasks.Add(t);
}
Console.WriteLine("All tasks have been added.");
// Do some work here.
try
{
Task.WaitAll(tasks.ToArray());
Console.WriteLine("All tasks have completed.");
}
catch (AggregateException ae)
{
foreach (var ex in ae.InnerExceptions)
Console.WriteLine(ex.Message);
}
finally
{
cts.Dispose();
}
// If needed, perform a final step after all tasks have completed.
Task.Factory.ContinueWhenAll(tasks.ToArray(), (arr) =>
{
foreach (var t in arr)
{
CompareFileData(t.Result);
}
});
}
public Task<string> GetFileStringAsync3(string path, CancellationToken token)
{
if (!File.Exists(path))
{
throw new FileNotFoundException(String.Format("Could not find {0}", path));
}
FileInfo fi = new FileInfo(path);
byte[] data = null;
if (fi.Length < MAX_FILE_SIZE && fi.Length > 0)
{
data = new byte[fi.Length];
}
else
{
throw new ArgumentException(String.Format("{0} is too big to load!", path));
}
FileStream fs = new FileStream(path, FileMode.Open, FileAccess.Read, FileShare.Read, data.Length, true);
// We still pass null for the last parameter because
// the state variable is visible to the continuation delegate.
Task<int> task = Task<int>.Factory.FromAsync(
fs.BeginRead, fs.EndRead, data, 0, data.Length, null);
return task.ContinueWith((antecedent) =>
{
fs.Close();
// If we did not receive the entire file, the end of the
// data buffer will contain garbage.
if (antecedent.Result < data.Length)
Array.Resize(ref data, antecedent.Result);
// Will be returned in the Result property of the Task<string>
// at some future point after the asynchronous file I/O operation completes.
return new UTF8Encoding().GetString(data);
});
}
string ProcessFileData(string data)
{
string s = data.Substring(0, 80);
Console.WriteLine(s);
return s;
}
string CompareFileData(string s)
{
return "compare results";
}
//</snippet11>
}sample · vbsamples/snippets/visualbasic/VS_Snippets_Misc/fromasync/vb/module1.vb01
Imports System.Collections.Generic
Imports System.IO
Imports System.Net
Imports System.Text
Imports System.Threading
Imports System.Threading.Tasks
Namespace specialNamespaceForOneMethodSignature
Class Task(Of TResult)
Public TValue As TResult
End Class
Class Dummy(Of TResult)
'<snippet01>
Public Function FromAsync(Of TArg1, TArg2, TArg3)(
ByVal beginMethod As Func(Of TArg1, TArg2, TArg3, AsyncCallback, Object, IAsyncResult),
ByVal endMethod As Func(Of IAsyncResult, TResult),
ByVal dataBuffer As TArg1,
ByVal byteOffsetToStartAt As TArg2,
ByVal maxBytesToRead As TArg3,
ByVal stateInfo As Object)
'</snippet01>
Return New Task(Of TResult)
End Function
End Class
End Namespace
Module Module1
Class AsyncResult
Public Sub New()
End Sub
'<snippet07>
Shared Function ReturnTaskFromAsyncResult() As Task(Of String)
Dim ar As IAsyncResult = DoSomethingAsynchronously()
Dim t As Task(Of String) = Task(Of String).Factory.FromAsync(ar, Function(res) CStr(res.AsyncState))
Return t
End Function
'</snippet07>
Private Shared Function DoSomethingAsynchronously() As IAsyncResult
Throw New NotImplementedException
End Function
End Class
'<snippet08>
Class WebDataDownLoader
Dim tcs As New TaskCompletionSource(Of String())
Dim nameToSearch As String
Dim token As CancellationToken
Dim results As New List(Of String)
Dim m_lock As Object
Dim count As Integer
Dim addresses() As String
Shared Sub Main()
Dim downloader As New WebDataDownLoader()
downloader.addresses = {"http://www.msnbc.com", "http://www.yahoo.com", _
"http://www.nytimes.com", "http://www.washingtonpost.com", _
"http://www.latimes.com", "http://www.newsday.com"}
Dim cts As New CancellationTokenSource()
' Create a UI thread from which to cancel the entire operation
Task.Factory.StartNew(Sub()
Console.WriteLine("Press c to cancel")
If Console.ReadKey().KeyChar = "c"c Then
cts.Cancel()
End If
End Sub)
' Using a neutral search term that is sure to get some hits on English web sites.
' Please substitute your favorite search term.
downloader.nameToSearch = "the"
Dim webTask As Task(Of String()) = downloader.GetWordCounts(downloader.addresses, downloader.nameToSearch, cts.Token)
' Do some other work here unless the method has already completed.
If (webTask.IsCompleted = False) Then
' Simulate some work
Thread.SpinWait(5000000)
End If
Dim results As String() = Nothing
Try
results = webTask.Result
Catch ae As AggregateException
For Each ex As Exception In ae.InnerExceptions
If (TypeOf (ex) Is OperationCanceledException) Then
Dim oce As OperationCanceledException = CType(ex, OperationCanceledException)
If oce.CancellationToken = cts.Token Then
Console.WriteLine("Operation canceled by user.")
End If
Else
Console.WriteLine(ex.Message)
End If
Next
Finally
cts.Dispose()
End Try
If (Not results Is Nothing) Then
For Each item As String In results
Console.WriteLine(item)
Next
End If
Console.WriteLine("Press any key to exit")
Console.ReadKey()
End Sub
Public Function GetWordCounts(ByVal urls() As String, ByVal str As String, ByVal token As CancellationToken) As Task(Of String())
Dim webClients() As WebClient
ReDim webClients(urls.Length)
m_lock = New Object()
' If the user cancels the CancellationToken, then we can use the
' WebClient's ability to cancel its own async operations.
token.Register(Sub()
For Each wc As WebClient In webClients
If Not wc Is Nothing Then
wc.CancelAsync()
End If
Next
End Sub)
For i As Integer = 0 To urls.Length - 1
webClients(i) = New WebClient()
' Specify the callback for the DownloadStringCompleted
' event that will be raised by this WebClient instance.
AddHandler webClients(i).DownloadStringCompleted, AddressOf WebEventHandler
Dim address As Uri = Nothing
Try
address = New Uri(urls(i))
' Pass the address, and also use it for the userToken
' to identify the page when the delegate is invoked.
webClients(i).DownloadStringAsync(address, address)
Catch ex As UriFormatException
tcs.TrySetException(ex)
Return tcs.Task
End Try
Next
' Return the underlying Task. The client code
' waits on the Result property, and handles exceptions
' in the try-catch block there.
Return tcs.Task
End Function
Public Sub WebEventHandler(ByVal sender As Object, ByVal args As DownloadStringCompletedEventArgs)
If args.Cancelled = True Then
tcs.TrySetCanceled()
Return
ElseIf Not args.Error Is Nothing Then
tcs.TrySetException(args.Error)
Return
Else
' Split the string into an array of words,
' then count the number of elements that match
' the search term.
Dim words() As String = args.Result.Split(" "c)
Dim NAME As String = nameToSearch.ToUpper()
Dim nameCount = (From word In words.AsParallel()
Where word.ToUpper().Contains(NAME)
Select word).Count()
' Associate the results with the url, and add new string to the array that
' the underlying Task object will return in its Result property.
results.Add(String.Format("{0} has {1} instances of {2}", args.UserState, nameCount, nameToSearch))
End If
SyncLock (m_lock)
count = count + 1
If (count = addresses.Length) Then
tcs.TrySetResult(results.ToArray())
End If
End SyncLock
End Sub
'</snippet08>
End Class
'<snippet09>
Class Calculator
Public Function BeginCalculate(ByVal decimalPlaces As Integer, ByVal ac As AsyncCallback, ByVal state As Object) As IAsyncResult
Console.WriteLine("Calling BeginCalculate on thread {0}", Thread.CurrentThread.ManagedThreadId)
Dim myTask = Task(Of String).Factory.StartNew(Function(obj) Compute(decimalPlaces), state)
myTask.ContinueWith(Sub(antecedent) ac(myTask))
End Function
Private Function Compute(ByVal decimalPlaces As Integer)
Console.WriteLine("Calling compute on thread {0}", Thread.CurrentThread.ManagedThreadId)
' Simulating some heavy work.
Thread.SpinWait(500000000)
' Actual implementation left as exercise for the reader.
' Several examples are available on the Web.
Return "3.14159265358979323846264338327950288"
End Function
Public Function EndCalculate(ByVal ar As IAsyncResult) As String
Console.WriteLine("Calling EndCalculate on thread {0}", Thread.CurrentThread.ManagedThreadId)
Return CType(ar, Task(Of String)).Result
End Function
End Class
Class CalculatorClient
Shared decimalPlaces As Integer
Shared Sub Main()
Dim calc As New Calculator
Dim places As Integer = 35
Dim callback As New AsyncCallback(AddressOf PrintResult)
Dim ar As IAsyncResult = calc.BeginCalculate(places, callback, calc)
' Do some work on this thread while the calculator is busy.
Console.WriteLine("Working...")
Thread.SpinWait(500000)
Console.ReadLine()
End Sub
Public Shared Sub PrintResult(ByVal result As IAsyncResult)
Dim c As Calculator = CType(result.AsyncState, Calculator)
Dim piString As String = c.EndCalculate(result)
Console.WriteLine("Calling PrintResult on thread {0}; result = {1}",
Thread.CurrentThread.ManagedThreadId, piString)
End Sub
End Class
'</snippet09>
Class FileStreamDemo
Shared Sub Main()
Dim fsd As New FileStreamDemo()
fsd.ShowCallingFromAsync()
End Sub
'<snippet03>
Const MAX_FILE_SIZE As Integer = 14000000
Shared Function GetFileStringAsync(ByVal path As String) As Task(Of String)
Dim fi As New FileInfo(path)
Dim data(fi.Length - 1) As Byte
Dim fs As FileStream = New FileStream(path, FileMode.Open, FileAccess.Read, FileShare.Read, data.Length, True)
' Task(Of Integer) returns the number of bytes read
Dim myTask As Task(Of Integer) = Task(Of Integer).Factory.FromAsync(
AddressOf fs.BeginRead, AddressOf fs.EndRead, data, 0, data.Length, Nothing)
' It is possible to do other work here while waiting
' for the antecedent task to complete.
' ...
' Add the continuation, which returns a Task<string>.
Return myTask.ContinueWith(Function(antecedent)
fs.Close()
If (antecedent.Result < 100) Then
Return "Data is too small to bother with."
End If
' If we did not receive the entire file, the end of the
' data buffer will contain garbage.
If (antecedent.Result < data.Length) Then
Array.Resize(data, antecedent.Result)
End If
' Will be returned in the Result property of the Task<string>
' at some future point after the asynchronous file I/O operation completes.
Return New UTF8Encoding().GetString(data)
End Function)
End Function
'</snippet03>
Public Sub ShowCallingFromAsync()
Dim path As String = "\\docbuild2\public\Main\Logs\DllDiffReport\DllDiffReport_BetweenInBuildAndInPublicShare.html"
'<snippet04>
Dim myTask As Task(Of String) = GetFileStringAsync(path)
' Do some other work
' ...
Try
Console.WriteLine(myTask.Result.Substring(0, 500))
Catch ex As AggregateException
Console.WriteLine(ex.InnerException.Message)
End Try
'</snippet04>
Console.WriteLine("Press Enter to exit.")
Console.ReadLine()
End Sub
'<snippet05>
Public Function GetFileStringAsync2(ByVal path As String) As Task(Of String)
Dim fi = New FileInfo(path)
Dim data(fi.Length - 1) As Byte
Dim state As New MyCustomState()
Dim fs As New FileStream(path, FileMode.Open, FileAccess.Read, FileShare.Read, data.Length, True)
' We still pass null for the last parameter because
' the state variable is visible to the continuation delegate.
Dim myTask As Task(Of Integer) = Task(Of Integer).Factory.FromAsync(
AddressOf fs.BeginRead, AddressOf fs.EndRead, data, 0, data.Length, Nothing)
Return myTask.ContinueWith(Function(antecedent)
fs.Close()
' Capture custom state data directly in the user delegate.
' No need to pass it through the FromAsync method.
If (state.StateData.Contains("New York, New York")) Then
Return "Start spreading the news!"
End If
' If we did not receive the entire file, the end of the
' data buffer will contain garbage.
If (antecedent.Result < data.Length) Then
Array.Resize(data, antecedent.Result)
End If
'/ Will be returned in the Result property of the Task<string>
'/ at some future point after the asynchronous file I/O operation completes.
Return New UTF8Encoding().GetString(data)
End Function)
End Function
'</snippet05>
'<snippet06>
Public Function GetMultiFileData(ByVal filesToRead As String()) As Task(Of String)
Dim fs As FileStream
Dim tasks(filesToRead.Length - 1) As Task(Of String)
Dim fileData() As Byte = Nothing
For i As Integer = 0 To filesToRead.Length
fileData(&H1000) = New Byte()
fs = New FileStream(filesToRead(i), FileMode.Open, FileAccess.Read, FileShare.Read, fileData.Length, True)
' By adding the continuation here, the
' Result of each task will be a string.
tasks(i) = Task(Of Integer).Factory.FromAsync(AddressOf fs.BeginRead,
AddressOf fs.EndRead,
fileData,
0,
fileData.Length,
Nothing).
ContinueWith(Function(antecedent)
fs.Close()
'If we did not receive the entire file, the end of the
' data buffer will contain garbage.
If (antecedent.Result < fileData.Length) Then
ReDim Preserve fileData(antecedent.Result)
End If
'Will be returned in the Result property of the Task<string>
' at some future point after the asynchronous file I/O operation completes.
Return New UTF8Encoding().GetString(fileData)
End Function)
Next
Return Task(Of String).Factory.ContinueWhenAll(tasks, Function(data)
' Propagate all exceptions and mark all faulted tasks as observed.
Task.WaitAll(data)
' Combine the results from all tasks.
Dim sb As New StringBuilder()
For Each t As Task(Of String) In data
sb.Append(t.Result)
Next
' Final result to be returned eventually on the calling thread.
Return sb.ToString()
End Function)
End Function
'</snippet06>
Class MyCustomState
Public StateData As String
Public Sub New()
StateData = "Hello"
End Sub
End Class
End Class
End ModuleThis overload takes three input parameters, as follows. The first parameter is a System.Func delegate that matches the signature of the System.IO.FileStream.BeginRead method. The second parameter is a System.Func delegate that takes an System.IAsyncResult and returns a TResult. Because System.IO.FileStream.EndRead returns an integer, the compiler infers the type of TResult as System.Int32 and the type of the task as System.Threading.Tasks.Task. The last four parameters are identical to those in the System.IO.FileStream.BeginRead method:
The buffer in which to store the file data.
The offset in the buffer at which to begin writing data.
The maximum amount of data to read from the file.
An optional object that stores user-defined state data to pass to the callback.
Use ContinueWith for the callback functionality
If you require access to the data in the file, as opposed to just the number of bytes, the System.Threading.Tasks.TaskFactory.FromAsync method is not sufficient. Instead, use System.Threading.Tasks.Task, whose Result property contains the file data. You can do this by adding a continuation to the original task. The continuation performs the work that would typically be performed by the System.AsyncCallback delegate. It is invoked when the antecedent completes, and the data buffer has been filled. (The System.IO.FileStream object should be closed before returning.)
The following example shows how to return a System.Threading.Tasks.Task that encapsulates the BeginRead/EndRead pair of the System.IO.FileStream class.
sample · csharpsamples/snippets/csharp/VS_Snippets_Misc/fromasync/cs/fromasync.cs03
using System;
using System.Collections.Concurrent;
using System.Collections.Generic;
using System.Diagnostics;
using System.IO;
using System.Linq;
using System.Text;
using System.Threading;
using System.Threading.Tasks;
using System.Net;
namespace specialNamespaceForOneMethodSignature
{
using System;
class Task<TResult>
{
public TResult TValue;
}
class Dummy <TResult>
{
// <snippet01>
public Task<TResult> FromAsync<TArg1, TArg2, TArg3>(
Func<TArg1, TArg2, TArg3, AsyncCallback, object, IAsyncResult> beginMethod, //BeginRead
Func<IAsyncResult, TResult> endMethod, //EndRead
TArg1 arg1, // the byte[] buffer
TArg2 arg2, // the offset in arg1 at which to start writing data
TArg3 arg3, // the maximum number of bytes to read
object state // optional state information
)
//</snippet01>
{ return new Task<TResult>(); }
}
}
namespace APM_Task
{
class TestFileStreamNaive
{
//<snippet02>
public string GetFileData(string path)
{
FileInfo fi = new FileInfo(path);
byte[] data = new byte[fi.Length];
FileStream fs;
// a using statement is ok here because we Wait before returning
// and will be done with the filestream.
using (fs = new FileStream(path, FileMode.Open, FileAccess.Read, FileShare.Read, data.Length, true))
{
//Task<int> returns the number of bytes read
Task<int> task = Task<int>.Factory.FromAsync(
fs.BeginRead, fs.EndRead, data, 0, data.Length, null);
task.Wait();
return new UTF8Encoding().GetString(data);
}
}
//</snippet02>
static void Main()
{
TestFileStreamNaive instance = new TestFileStreamNaive();
string s = instance.GetFileData("testfile.txt");
}
}
class AsyncResult : IAsyncResult
{
public AsyncResult() { }
public object AsyncState
{
get { return "Hello from a parallel universe."; }
}
public WaitHandle AsyncWaitHandle
{
get { throw new NotImplementedException(); }
}
public bool CompletedSynchronously
{
get { throw new NotImplementedException(); }
}
public bool IsCompleted
{
get { throw new NotImplementedException(); }
}
static IAsyncResult DoSomethingAsynchronously()
{
return new AsyncResult();
}
//<snippet07>
static Task<String> ReturnTaskFromAsyncResult()
{
IAsyncResult ar = DoSomethingAsynchronously();
Task<String> t = Task<string>.Factory.FromAsync(ar, _ =>
{
return (string)ar.AsyncState;
});
return t;
}
//</snippet07>
}
//<snippet08>
class WebDataDownloader
{
static void Main()
{
WebDataDownloader downloader = new WebDataDownloader();
string[] addresses = { "http://www.msnbc.com", "http://www.yahoo.com",
"http://www.nytimes.com", "http://www.washingtonpost.com",
"http://www.latimes.com", "http://www.newsday.com" };
CancellationTokenSource cts = new CancellationTokenSource();
// Create a UI thread from which to cancel the entire operation
Task.Factory.StartNew(() =>
{
Console.WriteLine("Press c to cancel");
if (Console.ReadKey().KeyChar == 'c')
cts.Cancel();
});
// Using a neutral search term that is sure to get some hits.
Task<string[]> webTask = downloader.GetWordCounts(addresses, "the", cts.Token);
// Do some other work here unless the method has already completed.
if (!webTask.IsCompleted)
{
// Simulate some work.
Thread.SpinWait(5000000);
}
string[] results = null;
try
{
results = webTask.Result;
}
catch (AggregateException e)
{
foreach (var ex in e.InnerExceptions)
{
OperationCanceledException oce = ex as OperationCanceledException;
if (oce != null)
{
if (oce.CancellationToken == cts.Token)
{
Console.WriteLine("Operation canceled by user.");
}
}
else
{
Console.WriteLine(ex.Message);
}
}
}
finally
{
cts.Dispose();
}
if (results != null)
{
foreach (var item in results)
Console.WriteLine(item);
}
Console.ReadKey();
}
Task<string[]> GetWordCounts(string[] urls, string name, CancellationToken token)
{
TaskCompletionSource<string[]> tcs = new TaskCompletionSource<string[]>();
WebClient[] webClients = new WebClient[urls.Length];
// If the user cancels the CancellationToken, then we can use the
// WebClient's ability to cancel its own async operations.
token.Register(() =>
{
foreach (var wc in webClients)
{
if (wc != null)
wc.CancelAsync();
}
});
object m_lock = new object();
int count = 0;
List<string> results = new List<string>();
for (int i = 0; i < urls.Length; i++)
{
webClients[i] = new WebClient();
#region callback
// Specify the callback for the DownloadStringCompleted
// event that will be raised by this WebClient instance.
webClients[i].DownloadStringCompleted += (obj, args) =>
{
if (args.Cancelled == true)
{
tcs.TrySetCanceled();
return;
}
else if (args.Error != null)
{
// Pass through to the underlying Task
// any exceptions thrown by the WebClient
// during the asynchronous operation.
tcs.TrySetException(args.Error);
return;
}
else
{
// Split the string into an array of words,
// then count the number of elements that match
// the search term.
string[] words = null;
words = args.Result.Split(' ');
string NAME = name.ToUpper();
int nameCount = (from word in words.AsParallel()
where word.ToUpper().Contains(NAME)
select word)
.Count();
// Associate the results with the url, and add new string to the array that
// the underlying Task object will return in its Result property.
results.Add(String.Format("{0} has {1} instances of {2}", args.UserState, nameCount, name));
}
// If this is the last async operation to complete,
// then set the Result property on the underlying Task.
lock (m_lock)
{
count++;
if (count == urls.Length)
{
tcs.TrySetResult(results.ToArray());
}
}
};
#endregion
// Call DownloadStringAsync for each URL.
Uri address = null;
try
{
address = new Uri(urls[i]);
// Pass the address, and also use it for the userToken
// to identify the page when the delegate is invoked.
webClients[i].DownloadStringAsync(address, address);
}
catch (UriFormatException ex)
{
// Abandon the entire operation if one url is malformed.
// Other actions are possible here.
tcs.TrySetException(ex);
return tcs.Task;
}
}
// Return the underlying Task. The client code
// waits on the Result property, and handles exceptions
// in the try-catch block there.
return tcs.Task;
}
//</snippet08>
}
#region snippet09
class Calculator
{
public IAsyncResult BeginCalculate(int decimalPlaces, AsyncCallback ac, object state)
{
Console.WriteLine($"Calling BeginCalculate on thread {Thread.CurrentThread.ManagedThreadId}");
Task<string> f = Task<string>.Factory.StartNew(_ => Compute(decimalPlaces), state);
if (ac != null) f.ContinueWith((res) => ac(f));
return f;
}
public string Compute(int numPlaces)
{
Console.WriteLine($"Calling compute on thread {Thread.CurrentThread.ManagedThreadId}");
// Simulating some heavy work.
Thread.SpinWait(500000000);
// Actual implementation left as exercise for the reader.
// Several examples are available on the Web.
return "3.14159265358979323846264338327950288";
}
public string EndCalculate(IAsyncResult ar)
{
Console.WriteLine($"Calling EndCalculate on thread {Thread.CurrentThread.ManagedThreadId}");
return ((Task<string>)ar).Result;
}
}
public class CalculatorClient
{
static int decimalPlaces = 12;
public static void Main()
{
Calculator calc = new Calculator();
int places = 35;
AsyncCallback callBack = new AsyncCallback(PrintResult);
IAsyncResult ar = calc.BeginCalculate(places, callBack, calc);
// Do some work on this thread while the calculator is busy.
Console.WriteLine("Working...");
Thread.SpinWait(500000);
Console.ReadLine();
}
public static void PrintResult(IAsyncResult result)
{
Calculator c = (Calculator)result.AsyncState;
string piString = c.EndCalculate(result);
Console.WriteLine($"Calling PrintResult on thread {Thread.CurrentThread.ManagedThreadId}; result = {piString}");
}
}
#endregion
} //end APM_Task namespace
class FileStreamDemo
{
static void Main()
{
FileStreamDemo fsd = new FileStreamDemo();
// var task = fsd.GetMultiFileData(new string[1]);
fsd.ShowCallingFromAsync();
// fsd.ShowCallingFromAsyncFileData();
// fsd.ProcessFilesAsync();
// task.Wait();
// Console.WriteLine(task.Result);
Console.WriteLine("press any key");
Console.ReadLine();
}
//<snippet03>
const int MAX_FILE_SIZE = 14000000;
public static Task<string> GetFileStringAsync(string path)
{
FileInfo fi = new FileInfo(path);
byte[] data = null;
data = new byte[fi.Length];
FileStream fs = new FileStream(path, FileMode.Open, FileAccess.Read, FileShare.Read, data.Length, true);
//Task<int> returns the number of bytes read
Task<int> task = Task<int>.Factory.FromAsync(
fs.BeginRead, fs.EndRead, data, 0, data.Length, null);
// It is possible to do other work here while waiting
// for the antecedent task to complete.
// ...
// Add the continuation, which returns a Task<string>.
return task.ContinueWith((antecedent) =>
{
fs.Close();
// Result = "number of bytes read" (if we need it.)
if (antecedent.Result < 100)
{
return "Data is too small to bother with.";
}
else
{
// If we did not receive the entire file, the end of the
// data buffer will contain garbage.
if (antecedent.Result < data.Length)
Array.Resize(ref data, antecedent.Result);
// Will be returned in the Result property of the Task<string>
// at some future point after the asynchronous file I/O operation completes.
return new UTF8Encoding().GetString(data);
}
});
}
//</snippet03>
void ShowCallingFromAsync()
{
string path = @"\\docbuild2\public\Main\Logs\DllDiffReport\DllDiffReport_BetweenInBuildAndInProduct.html";
//<snippet04>
Task<string> t = GetFileStringAsync(path);
// Do some other work:
// ...
try
{
Console.WriteLine(t.Result.Substring(0, 500));
}
catch (AggregateException ae)
{
Console.WriteLine(ae.InnerException.Message);
}
//</snippet04>
Console.ReadLine();
}
//not used???
//<snippet12>
public static Task<int> GetFileDataAsync(string path, ref byte[] data)
{
// Error handling omitted for brevity...
FileInfo fi = new FileInfo(path);
data = new byte[fi.Length];
FileStream fs = new FileStream(path, FileMode.Open, FileAccess.Read, FileShare.Read, data.Length, true);
// Task<int> returns the number of bytes read
// Pass FileStream in AsyncState parameter in order to close it from the call site.
return Task<int>.Factory.FromAsync(
fs.BeginRead, fs.EndRead, data, 0, data.Length, fs);
}
//</snippet12>
void ShowCallingFromAsyncFileData()
{
//<snippet13>
string path = @"\\remoteComputer\filename.txt";
byte[] buffer = null;
Task<int> t = GetFileDataAsync(path, ref buffer);
// Can do some other work here:
// ...
for(int i = 0; i < 10; i++)
Console.Write("Working... ");
var result =
t.ContinueWith((antecedent) =>
{
// Error handling omitted...
return new UTF8Encoding().GetString(buffer);
});
// Can also do some other work here:
// ...
for (int i = 0; i < 10; i++)
Console.Write("Working more... ");
try
{
t.Wait();
Console.WriteLine(result.Result.Substring(0, 50));
}
catch (AggregateException ae)
{
Console.WriteLine(ae.InnerException.Message);
}
//</snippet13>
Console.ReadLine();
}
// nested dummy class for snippet0 5 below
class MyCustomState
{
public string StateData { get; set; }
public MyCustomState() { StateData = "Hello"; }
}
private MyCustomState GetCustomState()
{
return new MyCustomState();
}
//<snippet05>
public Task<string> GetFileStringAsync2(string path)
{
FileInfo fi = new FileInfo(path);
byte[] data = new byte[fi.Length];
MyCustomState state = GetCustomState();
FileStream fs = new FileStream(path, FileMode.Open, FileAccess.Read, FileShare.Read, data.Length, true);
// We still pass null for the last parameter because
// the state variable is visible to the continuation delegate.
Task<int> task = Task<int>.Factory.FromAsync(
fs.BeginRead, fs.EndRead, data, 0, data.Length, null);
return task.ContinueWith((antecedent) =>
{
// It is safe to close the filestream now.
fs.Close();
// Capture custom state data directly in the user delegate.
// No need to pass it through the FromAsync method.
if (state.StateData.Contains("New York, New York"))
{
return "Start spreading the news!";
}
else
{
// If we did not receive the entire file, the end of the
// data buffer will contain garbage.
if (antecedent.Result < data.Length)
Array.Resize(ref data, antecedent.Result);
// Will be returned in the Result property of the Task<string>
// at some future point after the asynchronous file I/O operation completes.
return new UTF8Encoding().GetString(data);
}
});
}
//</snippet05>
string[] GetFilesToRead()
{
return new string[3] { "test.txt", "test1.txt", "test2.txt" };
}
//<snippet06>
public Task<string> GetMultiFileData(string[] filesToRead)
{
FileStream fs;
Task<string>[] tasks = new Task<string>[filesToRead.Length];
byte[] fileData = null;
for (int i = 0; i < filesToRead.Length; i++)
{
fileData = new byte[0x1000];
fs = new FileStream(filesToRead[i], FileMode.Open, FileAccess.Read, FileShare.Read, fileData.Length, true);
// By adding the continuation here, the
// Result of each task will be a string.
tasks[i] = Task<int>.Factory.FromAsync(
fs.BeginRead, fs.EndRead, fileData, 0, fileData.Length, null)
.ContinueWith((antecedent) =>
{
fs.Close();
// If we did not receive the entire file, the end of the
// data buffer will contain garbage.
if (antecedent.Result < fileData.Length)
Array.Resize(ref fileData, antecedent.Result);
// Will be returned in the Result property of the Task<string>
// at some future point after the asynchronous file I/O operation completes.
return new UTF8Encoding().GetString(fileData);
});
}
// Wait for all tasks to complete.
return Task<string>.Factory.ContinueWhenAll(tasks, (data) =>
{
// Propagate all exceptions and mark all faulted tasks as observed.
Task.WaitAll(data);
// Combine the results from all tasks.
StringBuilder sb = new StringBuilder();
foreach (var t in data)
{
sb.Append(t.Result);
}
// Final result to be returned eventually on the calling thread.
return sb.ToString();
});
}
//</snippet06>
public string ProcessData(Task[] arr)
{
return "processed";
}
//<snippet11>
void ProcessFilesAsync()
{
string[] files = Directory.GetFiles(@"\\remoteComputer\folderName\", "*.*", SearchOption.AllDirectories);
CancellationTokenSource cts = new CancellationTokenSource();
List<Task<string>> tasks = new List<Task<string>>();
foreach (var file in files)
{
Task<string> t = null;
try
{
t = GetFileStringAsync3(file, cts.Token);
}
catch
{
Console.WriteLine($"Argument exception on {file}");
continue;
}
t.ContinueWith((antecedent) => ProcessFileData(antecedent.Result));
tasks.Add(t);
}
Console.WriteLine("All tasks have been added.");
// Do some work here.
try
{
Task.WaitAll(tasks.ToArray());
Console.WriteLine("All tasks have completed.");
}
catch (AggregateException ae)
{
foreach (var ex in ae.InnerExceptions)
Console.WriteLine(ex.Message);
}
finally
{
cts.Dispose();
}
// If needed, perform a final step after all tasks have completed.
Task.Factory.ContinueWhenAll(tasks.ToArray(), (arr) =>
{
foreach (var t in arr)
{
CompareFileData(t.Result);
}
});
}
public Task<string> GetFileStringAsync3(string path, CancellationToken token)
{
if (!File.Exists(path))
{
throw new FileNotFoundException(String.Format("Could not find {0}", path));
}
FileInfo fi = new FileInfo(path);
byte[] data = null;
if (fi.Length < MAX_FILE_SIZE && fi.Length > 0)
{
data = new byte[fi.Length];
}
else
{
throw new ArgumentException(String.Format("{0} is too big to load!", path));
}
FileStream fs = new FileStream(path, FileMode.Open, FileAccess.Read, FileShare.Read, data.Length, true);
// We still pass null for the last parameter because
// the state variable is visible to the continuation delegate.
Task<int> task = Task<int>.Factory.FromAsync(
fs.BeginRead, fs.EndRead, data, 0, data.Length, null);
return task.ContinueWith((antecedent) =>
{
fs.Close();
// If we did not receive the entire file, the end of the
// data buffer will contain garbage.
if (antecedent.Result < data.Length)
Array.Resize(ref data, antecedent.Result);
// Will be returned in the Result property of the Task<string>
// at some future point after the asynchronous file I/O operation completes.
return new UTF8Encoding().GetString(data);
});
}
string ProcessFileData(string data)
{
string s = data.Substring(0, 80);
Console.WriteLine(s);
return s;
}
string CompareFileData(string s)
{
return "compare results";
}
//</snippet11>
}sample · vbsamples/snippets/visualbasic/VS_Snippets_Misc/fromasync/vb/module1.vb03
Imports System.Collections.Generic
Imports System.IO
Imports System.Net
Imports System.Text
Imports System.Threading
Imports System.Threading.Tasks
Namespace specialNamespaceForOneMethodSignature
Class Task(Of TResult)
Public TValue As TResult
End Class
Class Dummy(Of TResult)
'<snippet01>
Public Function FromAsync(Of TArg1, TArg2, TArg3)(
ByVal beginMethod As Func(Of TArg1, TArg2, TArg3, AsyncCallback, Object, IAsyncResult),
ByVal endMethod As Func(Of IAsyncResult, TResult),
ByVal dataBuffer As TArg1,
ByVal byteOffsetToStartAt As TArg2,
ByVal maxBytesToRead As TArg3,
ByVal stateInfo As Object)
'</snippet01>
Return New Task(Of TResult)
End Function
End Class
End Namespace
Module Module1
Class AsyncResult
Public Sub New()
End Sub
'<snippet07>
Shared Function ReturnTaskFromAsyncResult() As Task(Of String)
Dim ar As IAsyncResult = DoSomethingAsynchronously()
Dim t As Task(Of String) = Task(Of String).Factory.FromAsync(ar, Function(res) CStr(res.AsyncState))
Return t
End Function
'</snippet07>
Private Shared Function DoSomethingAsynchronously() As IAsyncResult
Throw New NotImplementedException
End Function
End Class
'<snippet08>
Class WebDataDownLoader
Dim tcs As New TaskCompletionSource(Of String())
Dim nameToSearch As String
Dim token As CancellationToken
Dim results As New List(Of String)
Dim m_lock As Object
Dim count As Integer
Dim addresses() As String
Shared Sub Main()
Dim downloader As New WebDataDownLoader()
downloader.addresses = {"http://www.msnbc.com", "http://www.yahoo.com", _
"http://www.nytimes.com", "http://www.washingtonpost.com", _
"http://www.latimes.com", "http://www.newsday.com"}
Dim cts As New CancellationTokenSource()
' Create a UI thread from which to cancel the entire operation
Task.Factory.StartNew(Sub()
Console.WriteLine("Press c to cancel")
If Console.ReadKey().KeyChar = "c"c Then
cts.Cancel()
End If
End Sub)
' Using a neutral search term that is sure to get some hits on English web sites.
' Please substitute your favorite search term.
downloader.nameToSearch = "the"
Dim webTask As Task(Of String()) = downloader.GetWordCounts(downloader.addresses, downloader.nameToSearch, cts.Token)
' Do some other work here unless the method has already completed.
If (webTask.IsCompleted = False) Then
' Simulate some work
Thread.SpinWait(5000000)
End If
Dim results As String() = Nothing
Try
results = webTask.Result
Catch ae As AggregateException
For Each ex As Exception In ae.InnerExceptions
If (TypeOf (ex) Is OperationCanceledException) Then
Dim oce As OperationCanceledException = CType(ex, OperationCanceledException)
If oce.CancellationToken = cts.Token Then
Console.WriteLine("Operation canceled by user.")
End If
Else
Console.WriteLine(ex.Message)
End If
Next
Finally
cts.Dispose()
End Try
If (Not results Is Nothing) Then
For Each item As String In results
Console.WriteLine(item)
Next
End If
Console.WriteLine("Press any key to exit")
Console.ReadKey()
End Sub
Public Function GetWordCounts(ByVal urls() As String, ByVal str As String, ByVal token As CancellationToken) As Task(Of String())
Dim webClients() As WebClient
ReDim webClients(urls.Length)
m_lock = New Object()
' If the user cancels the CancellationToken, then we can use the
' WebClient's ability to cancel its own async operations.
token.Register(Sub()
For Each wc As WebClient In webClients
If Not wc Is Nothing Then
wc.CancelAsync()
End If
Next
End Sub)
For i As Integer = 0 To urls.Length - 1
webClients(i) = New WebClient()
' Specify the callback for the DownloadStringCompleted
' event that will be raised by this WebClient instance.
AddHandler webClients(i).DownloadStringCompleted, AddressOf WebEventHandler
Dim address As Uri = Nothing
Try
address = New Uri(urls(i))
' Pass the address, and also use it for the userToken
' to identify the page when the delegate is invoked.
webClients(i).DownloadStringAsync(address, address)
Catch ex As UriFormatException
tcs.TrySetException(ex)
Return tcs.Task
End Try
Next
' Return the underlying Task. The client code
' waits on the Result property, and handles exceptions
' in the try-catch block there.
Return tcs.Task
End Function
Public Sub WebEventHandler(ByVal sender As Object, ByVal args As DownloadStringCompletedEventArgs)
If args.Cancelled = True Then
tcs.TrySetCanceled()
Return
ElseIf Not args.Error Is Nothing Then
tcs.TrySetException(args.Error)
Return
Else
' Split the string into an array of words,
' then count the number of elements that match
' the search term.
Dim words() As String = args.Result.Split(" "c)
Dim NAME As String = nameToSearch.ToUpper()
Dim nameCount = (From word In words.AsParallel()
Where word.ToUpper().Contains(NAME)
Select word).Count()
' Associate the results with the url, and add new string to the array that
' the underlying Task object will return in its Result property.
results.Add(String.Format("{0} has {1} instances of {2}", args.UserState, nameCount, nameToSearch))
End If
SyncLock (m_lock)
count = count + 1
If (count = addresses.Length) Then
tcs.TrySetResult(results.ToArray())
End If
End SyncLock
End Sub
'</snippet08>
End Class
'<snippet09>
Class Calculator
Public Function BeginCalculate(ByVal decimalPlaces As Integer, ByVal ac As AsyncCallback, ByVal state As Object) As IAsyncResult
Console.WriteLine("Calling BeginCalculate on thread {0}", Thread.CurrentThread.ManagedThreadId)
Dim myTask = Task(Of String).Factory.StartNew(Function(obj) Compute(decimalPlaces), state)
myTask.ContinueWith(Sub(antecedent) ac(myTask))
End Function
Private Function Compute(ByVal decimalPlaces As Integer)
Console.WriteLine("Calling compute on thread {0}", Thread.CurrentThread.ManagedThreadId)
' Simulating some heavy work.
Thread.SpinWait(500000000)
' Actual implementation left as exercise for the reader.
' Several examples are available on the Web.
Return "3.14159265358979323846264338327950288"
End Function
Public Function EndCalculate(ByVal ar As IAsyncResult) As String
Console.WriteLine("Calling EndCalculate on thread {0}", Thread.CurrentThread.ManagedThreadId)
Return CType(ar, Task(Of String)).Result
End Function
End Class
Class CalculatorClient
Shared decimalPlaces As Integer
Shared Sub Main()
Dim calc As New Calculator
Dim places As Integer = 35
Dim callback As New AsyncCallback(AddressOf PrintResult)
Dim ar As IAsyncResult = calc.BeginCalculate(places, callback, calc)
' Do some work on this thread while the calculator is busy.
Console.WriteLine("Working...")
Thread.SpinWait(500000)
Console.ReadLine()
End Sub
Public Shared Sub PrintResult(ByVal result As IAsyncResult)
Dim c As Calculator = CType(result.AsyncState, Calculator)
Dim piString As String = c.EndCalculate(result)
Console.WriteLine("Calling PrintResult on thread {0}; result = {1}",
Thread.CurrentThread.ManagedThreadId, piString)
End Sub
End Class
'</snippet09>
Class FileStreamDemo
Shared Sub Main()
Dim fsd As New FileStreamDemo()
fsd.ShowCallingFromAsync()
End Sub
'<snippet03>
Const MAX_FILE_SIZE As Integer = 14000000
Shared Function GetFileStringAsync(ByVal path As String) As Task(Of String)
Dim fi As New FileInfo(path)
Dim data(fi.Length - 1) As Byte
Dim fs As FileStream = New FileStream(path, FileMode.Open, FileAccess.Read, FileShare.Read, data.Length, True)
' Task(Of Integer) returns the number of bytes read
Dim myTask As Task(Of Integer) = Task(Of Integer).Factory.FromAsync(
AddressOf fs.BeginRead, AddressOf fs.EndRead, data, 0, data.Length, Nothing)
' It is possible to do other work here while waiting
' for the antecedent task to complete.
' ...
' Add the continuation, which returns a Task<string>.
Return myTask.ContinueWith(Function(antecedent)
fs.Close()
If (antecedent.Result < 100) Then
Return "Data is too small to bother with."
End If
' If we did not receive the entire file, the end of the
' data buffer will contain garbage.
If (antecedent.Result < data.Length) Then
Array.Resize(data, antecedent.Result)
End If
' Will be returned in the Result property of the Task<string>
' at some future point after the asynchronous file I/O operation completes.
Return New UTF8Encoding().GetString(data)
End Function)
End Function
'</snippet03>
Public Sub ShowCallingFromAsync()
Dim path As String = "\\docbuild2\public\Main\Logs\DllDiffReport\DllDiffReport_BetweenInBuildAndInPublicShare.html"
'<snippet04>
Dim myTask As Task(Of String) = GetFileStringAsync(path)
' Do some other work
' ...
Try
Console.WriteLine(myTask.Result.Substring(0, 500))
Catch ex As AggregateException
Console.WriteLine(ex.InnerException.Message)
End Try
'</snippet04>
Console.WriteLine("Press Enter to exit.")
Console.ReadLine()
End Sub
'<snippet05>
Public Function GetFileStringAsync2(ByVal path As String) As Task(Of String)
Dim fi = New FileInfo(path)
Dim data(fi.Length - 1) As Byte
Dim state As New MyCustomState()
Dim fs As New FileStream(path, FileMode.Open, FileAccess.Read, FileShare.Read, data.Length, True)
' We still pass null for the last parameter because
' the state variable is visible to the continuation delegate.
Dim myTask As Task(Of Integer) = Task(Of Integer).Factory.FromAsync(
AddressOf fs.BeginRead, AddressOf fs.EndRead, data, 0, data.Length, Nothing)
Return myTask.ContinueWith(Function(antecedent)
fs.Close()
' Capture custom state data directly in the user delegate.
' No need to pass it through the FromAsync method.
If (state.StateData.Contains("New York, New York")) Then
Return "Start spreading the news!"
End If
' If we did not receive the entire file, the end of the
' data buffer will contain garbage.
If (antecedent.Result < data.Length) Then
Array.Resize(data, antecedent.Result)
End If
'/ Will be returned in the Result property of the Task<string>
'/ at some future point after the asynchronous file I/O operation completes.
Return New UTF8Encoding().GetString(data)
End Function)
End Function
'</snippet05>
'<snippet06>
Public Function GetMultiFileData(ByVal filesToRead As String()) As Task(Of String)
Dim fs As FileStream
Dim tasks(filesToRead.Length - 1) As Task(Of String)
Dim fileData() As Byte = Nothing
For i As Integer = 0 To filesToRead.Length
fileData(&H1000) = New Byte()
fs = New FileStream(filesToRead(i), FileMode.Open, FileAccess.Read, FileShare.Read, fileData.Length, True)
' By adding the continuation here, the
' Result of each task will be a string.
tasks(i) = Task(Of Integer).Factory.FromAsync(AddressOf fs.BeginRead,
AddressOf fs.EndRead,
fileData,
0,
fileData.Length,
Nothing).
ContinueWith(Function(antecedent)
fs.Close()
'If we did not receive the entire file, the end of the
' data buffer will contain garbage.
If (antecedent.Result < fileData.Length) Then
ReDim Preserve fileData(antecedent.Result)
End If
'Will be returned in the Result property of the Task<string>
' at some future point after the asynchronous file I/O operation completes.
Return New UTF8Encoding().GetString(fileData)
End Function)
Next
Return Task(Of String).Factory.ContinueWhenAll(tasks, Function(data)
' Propagate all exceptions and mark all faulted tasks as observed.
Task.WaitAll(data)
' Combine the results from all tasks.
Dim sb As New StringBuilder()
For Each t As Task(Of String) In data
sb.Append(t.Result)
Next
' Final result to be returned eventually on the calling thread.
Return sb.ToString()
End Function)
End Function
'</snippet06>
Class MyCustomState
Public StateData As String
Public Sub New()
StateData = "Hello"
End Sub
End Class
End Class
End ModuleThe method can then be called, as follows.
sample · csharpsamples/snippets/csharp/VS_Snippets_Misc/fromasync/cs/fromasync.cs04
using System;
using System.Collections.Concurrent;
using System.Collections.Generic;
using System.Diagnostics;
using System.IO;
using System.Linq;
using System.Text;
using System.Threading;
using System.Threading.Tasks;
using System.Net;
namespace specialNamespaceForOneMethodSignature
{
using System;
class Task<TResult>
{
public TResult TValue;
}
class Dummy <TResult>
{
// <snippet01>
public Task<TResult> FromAsync<TArg1, TArg2, TArg3>(
Func<TArg1, TArg2, TArg3, AsyncCallback, object, IAsyncResult> beginMethod, //BeginRead
Func<IAsyncResult, TResult> endMethod, //EndRead
TArg1 arg1, // the byte[] buffer
TArg2 arg2, // the offset in arg1 at which to start writing data
TArg3 arg3, // the maximum number of bytes to read
object state // optional state information
)
//</snippet01>
{ return new Task<TResult>(); }
}
}
namespace APM_Task
{
class TestFileStreamNaive
{
//<snippet02>
public string GetFileData(string path)
{
FileInfo fi = new FileInfo(path);
byte[] data = new byte[fi.Length];
FileStream fs;
// a using statement is ok here because we Wait before returning
// and will be done with the filestream.
using (fs = new FileStream(path, FileMode.Open, FileAccess.Read, FileShare.Read, data.Length, true))
{
//Task<int> returns the number of bytes read
Task<int> task = Task<int>.Factory.FromAsync(
fs.BeginRead, fs.EndRead, data, 0, data.Length, null);
task.Wait();
return new UTF8Encoding().GetString(data);
}
}
//</snippet02>
static void Main()
{
TestFileStreamNaive instance = new TestFileStreamNaive();
string s = instance.GetFileData("testfile.txt");
}
}
class AsyncResult : IAsyncResult
{
public AsyncResult() { }
public object AsyncState
{
get { return "Hello from a parallel universe."; }
}
public WaitHandle AsyncWaitHandle
{
get { throw new NotImplementedException(); }
}
public bool CompletedSynchronously
{
get { throw new NotImplementedException(); }
}
public bool IsCompleted
{
get { throw new NotImplementedException(); }
}
static IAsyncResult DoSomethingAsynchronously()
{
return new AsyncResult();
}
//<snippet07>
static Task<String> ReturnTaskFromAsyncResult()
{
IAsyncResult ar = DoSomethingAsynchronously();
Task<String> t = Task<string>.Factory.FromAsync(ar, _ =>
{
return (string)ar.AsyncState;
});
return t;
}
//</snippet07>
}
//<snippet08>
class WebDataDownloader
{
static void Main()
{
WebDataDownloader downloader = new WebDataDownloader();
string[] addresses = { "http://www.msnbc.com", "http://www.yahoo.com",
"http://www.nytimes.com", "http://www.washingtonpost.com",
"http://www.latimes.com", "http://www.newsday.com" };
CancellationTokenSource cts = new CancellationTokenSource();
// Create a UI thread from which to cancel the entire operation
Task.Factory.StartNew(() =>
{
Console.WriteLine("Press c to cancel");
if (Console.ReadKey().KeyChar == 'c')
cts.Cancel();
});
// Using a neutral search term that is sure to get some hits.
Task<string[]> webTask = downloader.GetWordCounts(addresses, "the", cts.Token);
// Do some other work here unless the method has already completed.
if (!webTask.IsCompleted)
{
// Simulate some work.
Thread.SpinWait(5000000);
}
string[] results = null;
try
{
results = webTask.Result;
}
catch (AggregateException e)
{
foreach (var ex in e.InnerExceptions)
{
OperationCanceledException oce = ex as OperationCanceledException;
if (oce != null)
{
if (oce.CancellationToken == cts.Token)
{
Console.WriteLine("Operation canceled by user.");
}
}
else
{
Console.WriteLine(ex.Message);
}
}
}
finally
{
cts.Dispose();
}
if (results != null)
{
foreach (var item in results)
Console.WriteLine(item);
}
Console.ReadKey();
}
Task<string[]> GetWordCounts(string[] urls, string name, CancellationToken token)
{
TaskCompletionSource<string[]> tcs = new TaskCompletionSource<string[]>();
WebClient[] webClients = new WebClient[urls.Length];
// If the user cancels the CancellationToken, then we can use the
// WebClient's ability to cancel its own async operations.
token.Register(() =>
{
foreach (var wc in webClients)
{
if (wc != null)
wc.CancelAsync();
}
});
object m_lock = new object();
int count = 0;
List<string> results = new List<string>();
for (int i = 0; i < urls.Length; i++)
{
webClients[i] = new WebClient();
#region callback
// Specify the callback for the DownloadStringCompleted
// event that will be raised by this WebClient instance.
webClients[i].DownloadStringCompleted += (obj, args) =>
{
if (args.Cancelled == true)
{
tcs.TrySetCanceled();
return;
}
else if (args.Error != null)
{
// Pass through to the underlying Task
// any exceptions thrown by the WebClient
// during the asynchronous operation.
tcs.TrySetException(args.Error);
return;
}
else
{
// Split the string into an array of words,
// then count the number of elements that match
// the search term.
string[] words = null;
words = args.Result.Split(' ');
string NAME = name.ToUpper();
int nameCount = (from word in words.AsParallel()
where word.ToUpper().Contains(NAME)
select word)
.Count();
// Associate the results with the url, and add new string to the array that
// the underlying Task object will return in its Result property.
results.Add(String.Format("{0} has {1} instances of {2}", args.UserState, nameCount, name));
}
// If this is the last async operation to complete,
// then set the Result property on the underlying Task.
lock (m_lock)
{
count++;
if (count == urls.Length)
{
tcs.TrySetResult(results.ToArray());
}
}
};
#endregion
// Call DownloadStringAsync for each URL.
Uri address = null;
try
{
address = new Uri(urls[i]);
// Pass the address, and also use it for the userToken
// to identify the page when the delegate is invoked.
webClients[i].DownloadStringAsync(address, address);
}
catch (UriFormatException ex)
{
// Abandon the entire operation if one url is malformed.
// Other actions are possible here.
tcs.TrySetException(ex);
return tcs.Task;
}
}
// Return the underlying Task. The client code
// waits on the Result property, and handles exceptions
// in the try-catch block there.
return tcs.Task;
}
//</snippet08>
}
#region snippet09
class Calculator
{
public IAsyncResult BeginCalculate(int decimalPlaces, AsyncCallback ac, object state)
{
Console.WriteLine($"Calling BeginCalculate on thread {Thread.CurrentThread.ManagedThreadId}");
Task<string> f = Task<string>.Factory.StartNew(_ => Compute(decimalPlaces), state);
if (ac != null) f.ContinueWith((res) => ac(f));
return f;
}
public string Compute(int numPlaces)
{
Console.WriteLine($"Calling compute on thread {Thread.CurrentThread.ManagedThreadId}");
// Simulating some heavy work.
Thread.SpinWait(500000000);
// Actual implementation left as exercise for the reader.
// Several examples are available on the Web.
return "3.14159265358979323846264338327950288";
}
public string EndCalculate(IAsyncResult ar)
{
Console.WriteLine($"Calling EndCalculate on thread {Thread.CurrentThread.ManagedThreadId}");
return ((Task<string>)ar).Result;
}
}
public class CalculatorClient
{
static int decimalPlaces = 12;
public static void Main()
{
Calculator calc = new Calculator();
int places = 35;
AsyncCallback callBack = new AsyncCallback(PrintResult);
IAsyncResult ar = calc.BeginCalculate(places, callBack, calc);
// Do some work on this thread while the calculator is busy.
Console.WriteLine("Working...");
Thread.SpinWait(500000);
Console.ReadLine();
}
public static void PrintResult(IAsyncResult result)
{
Calculator c = (Calculator)result.AsyncState;
string piString = c.EndCalculate(result);
Console.WriteLine($"Calling PrintResult on thread {Thread.CurrentThread.ManagedThreadId}; result = {piString}");
}
}
#endregion
} //end APM_Task namespace
class FileStreamDemo
{
static void Main()
{
FileStreamDemo fsd = new FileStreamDemo();
// var task = fsd.GetMultiFileData(new string[1]);
fsd.ShowCallingFromAsync();
// fsd.ShowCallingFromAsyncFileData();
// fsd.ProcessFilesAsync();
// task.Wait();
// Console.WriteLine(task.Result);
Console.WriteLine("press any key");
Console.ReadLine();
}
//<snippet03>
const int MAX_FILE_SIZE = 14000000;
public static Task<string> GetFileStringAsync(string path)
{
FileInfo fi = new FileInfo(path);
byte[] data = null;
data = new byte[fi.Length];
FileStream fs = new FileStream(path, FileMode.Open, FileAccess.Read, FileShare.Read, data.Length, true);
//Task<int> returns the number of bytes read
Task<int> task = Task<int>.Factory.FromAsync(
fs.BeginRead, fs.EndRead, data, 0, data.Length, null);
// It is possible to do other work here while waiting
// for the antecedent task to complete.
// ...
// Add the continuation, which returns a Task<string>.
return task.ContinueWith((antecedent) =>
{
fs.Close();
// Result = "number of bytes read" (if we need it.)
if (antecedent.Result < 100)
{
return "Data is too small to bother with.";
}
else
{
// If we did not receive the entire file, the end of the
// data buffer will contain garbage.
if (antecedent.Result < data.Length)
Array.Resize(ref data, antecedent.Result);
// Will be returned in the Result property of the Task<string>
// at some future point after the asynchronous file I/O operation completes.
return new UTF8Encoding().GetString(data);
}
});
}
//</snippet03>
void ShowCallingFromAsync()
{
string path = @"\\docbuild2\public\Main\Logs\DllDiffReport\DllDiffReport_BetweenInBuildAndInProduct.html";
//<snippet04>
Task<string> t = GetFileStringAsync(path);
// Do some other work:
// ...
try
{
Console.WriteLine(t.Result.Substring(0, 500));
}
catch (AggregateException ae)
{
Console.WriteLine(ae.InnerException.Message);
}
//</snippet04>
Console.ReadLine();
}
//not used???
//<snippet12>
public static Task<int> GetFileDataAsync(string path, ref byte[] data)
{
// Error handling omitted for brevity...
FileInfo fi = new FileInfo(path);
data = new byte[fi.Length];
FileStream fs = new FileStream(path, FileMode.Open, FileAccess.Read, FileShare.Read, data.Length, true);
// Task<int> returns the number of bytes read
// Pass FileStream in AsyncState parameter in order to close it from the call site.
return Task<int>.Factory.FromAsync(
fs.BeginRead, fs.EndRead, data, 0, data.Length, fs);
}
//</snippet12>
void ShowCallingFromAsyncFileData()
{
//<snippet13>
string path = @"\\remoteComputer\filename.txt";
byte[] buffer = null;
Task<int> t = GetFileDataAsync(path, ref buffer);
// Can do some other work here:
// ...
for(int i = 0; i < 10; i++)
Console.Write("Working... ");
var result =
t.ContinueWith((antecedent) =>
{
// Error handling omitted...
return new UTF8Encoding().GetString(buffer);
});
// Can also do some other work here:
// ...
for (int i = 0; i < 10; i++)
Console.Write("Working more... ");
try
{
t.Wait();
Console.WriteLine(result.Result.Substring(0, 50));
}
catch (AggregateException ae)
{
Console.WriteLine(ae.InnerException.Message);
}
//</snippet13>
Console.ReadLine();
}
// nested dummy class for snippet0 5 below
class MyCustomState
{
public string StateData { get; set; }
public MyCustomState() { StateData = "Hello"; }
}
private MyCustomState GetCustomState()
{
return new MyCustomState();
}
//<snippet05>
public Task<string> GetFileStringAsync2(string path)
{
FileInfo fi = new FileInfo(path);
byte[] data = new byte[fi.Length];
MyCustomState state = GetCustomState();
FileStream fs = new FileStream(path, FileMode.Open, FileAccess.Read, FileShare.Read, data.Length, true);
// We still pass null for the last parameter because
// the state variable is visible to the continuation delegate.
Task<int> task = Task<int>.Factory.FromAsync(
fs.BeginRead, fs.EndRead, data, 0, data.Length, null);
return task.ContinueWith((antecedent) =>
{
// It is safe to close the filestream now.
fs.Close();
// Capture custom state data directly in the user delegate.
// No need to pass it through the FromAsync method.
if (state.StateData.Contains("New York, New York"))
{
return "Start spreading the news!";
}
else
{
// If we did not receive the entire file, the end of the
// data buffer will contain garbage.
if (antecedent.Result < data.Length)
Array.Resize(ref data, antecedent.Result);
// Will be returned in the Result property of the Task<string>
// at some future point after the asynchronous file I/O operation completes.
return new UTF8Encoding().GetString(data);
}
});
}
//</snippet05>
string[] GetFilesToRead()
{
return new string[3] { "test.txt", "test1.txt", "test2.txt" };
}
//<snippet06>
public Task<string> GetMultiFileData(string[] filesToRead)
{
FileStream fs;
Task<string>[] tasks = new Task<string>[filesToRead.Length];
byte[] fileData = null;
for (int i = 0; i < filesToRead.Length; i++)
{
fileData = new byte[0x1000];
fs = new FileStream(filesToRead[i], FileMode.Open, FileAccess.Read, FileShare.Read, fileData.Length, true);
// By adding the continuation here, the
// Result of each task will be a string.
tasks[i] = Task<int>.Factory.FromAsync(
fs.BeginRead, fs.EndRead, fileData, 0, fileData.Length, null)
.ContinueWith((antecedent) =>
{
fs.Close();
// If we did not receive the entire file, the end of the
// data buffer will contain garbage.
if (antecedent.Result < fileData.Length)
Array.Resize(ref fileData, antecedent.Result);
// Will be returned in the Result property of the Task<string>
// at some future point after the asynchronous file I/O operation completes.
return new UTF8Encoding().GetString(fileData);
});
}
// Wait for all tasks to complete.
return Task<string>.Factory.ContinueWhenAll(tasks, (data) =>
{
// Propagate all exceptions and mark all faulted tasks as observed.
Task.WaitAll(data);
// Combine the results from all tasks.
StringBuilder sb = new StringBuilder();
foreach (var t in data)
{
sb.Append(t.Result);
}
// Final result to be returned eventually on the calling thread.
return sb.ToString();
});
}
//</snippet06>
public string ProcessData(Task[] arr)
{
return "processed";
}
//<snippet11>
void ProcessFilesAsync()
{
string[] files = Directory.GetFiles(@"\\remoteComputer\folderName\", "*.*", SearchOption.AllDirectories);
CancellationTokenSource cts = new CancellationTokenSource();
List<Task<string>> tasks = new List<Task<string>>();
foreach (var file in files)
{
Task<string> t = null;
try
{
t = GetFileStringAsync3(file, cts.Token);
}
catch
{
Console.WriteLine($"Argument exception on {file}");
continue;
}
t.ContinueWith((antecedent) => ProcessFileData(antecedent.Result));
tasks.Add(t);
}
Console.WriteLine("All tasks have been added.");
// Do some work here.
try
{
Task.WaitAll(tasks.ToArray());
Console.WriteLine("All tasks have completed.");
}
catch (AggregateException ae)
{
foreach (var ex in ae.InnerExceptions)
Console.WriteLine(ex.Message);
}
finally
{
cts.Dispose();
}
// If needed, perform a final step after all tasks have completed.
Task.Factory.ContinueWhenAll(tasks.ToArray(), (arr) =>
{
foreach (var t in arr)
{
CompareFileData(t.Result);
}
});
}
public Task<string> GetFileStringAsync3(string path, CancellationToken token)
{
if (!File.Exists(path))
{
throw new FileNotFoundException(String.Format("Could not find {0}", path));
}
FileInfo fi = new FileInfo(path);
byte[] data = null;
if (fi.Length < MAX_FILE_SIZE && fi.Length > 0)
{
data = new byte[fi.Length];
}
else
{
throw new ArgumentException(String.Format("{0} is too big to load!", path));
}
FileStream fs = new FileStream(path, FileMode.Open, FileAccess.Read, FileShare.Read, data.Length, true);
// We still pass null for the last parameter because
// the state variable is visible to the continuation delegate.
Task<int> task = Task<int>.Factory.FromAsync(
fs.BeginRead, fs.EndRead, data, 0, data.Length, null);
return task.ContinueWith((antecedent) =>
{
fs.Close();
// If we did not receive the entire file, the end of the
// data buffer will contain garbage.
if (antecedent.Result < data.Length)
Array.Resize(ref data, antecedent.Result);
// Will be returned in the Result property of the Task<string>
// at some future point after the asynchronous file I/O operation completes.
return new UTF8Encoding().GetString(data);
});
}
string ProcessFileData(string data)
{
string s = data.Substring(0, 80);
Console.WriteLine(s);
return s;
}
string CompareFileData(string s)
{
return "compare results";
}
//</snippet11>
}sample · vbsamples/snippets/visualbasic/VS_Snippets_Misc/fromasync/vb/module1.vb04
Imports System.Collections.Generic
Imports System.IO
Imports System.Net
Imports System.Text
Imports System.Threading
Imports System.Threading.Tasks
Namespace specialNamespaceForOneMethodSignature
Class Task(Of TResult)
Public TValue As TResult
End Class
Class Dummy(Of TResult)
'<snippet01>
Public Function FromAsync(Of TArg1, TArg2, TArg3)(
ByVal beginMethod As Func(Of TArg1, TArg2, TArg3, AsyncCallback, Object, IAsyncResult),
ByVal endMethod As Func(Of IAsyncResult, TResult),
ByVal dataBuffer As TArg1,
ByVal byteOffsetToStartAt As TArg2,
ByVal maxBytesToRead As TArg3,
ByVal stateInfo As Object)
'</snippet01>
Return New Task(Of TResult)
End Function
End Class
End Namespace
Module Module1
Class AsyncResult
Public Sub New()
End Sub
'<snippet07>
Shared Function ReturnTaskFromAsyncResult() As Task(Of String)
Dim ar As IAsyncResult = DoSomethingAsynchronously()
Dim t As Task(Of String) = Task(Of String).Factory.FromAsync(ar, Function(res) CStr(res.AsyncState))
Return t
End Function
'</snippet07>
Private Shared Function DoSomethingAsynchronously() As IAsyncResult
Throw New NotImplementedException
End Function
End Class
'<snippet08>
Class WebDataDownLoader
Dim tcs As New TaskCompletionSource(Of String())
Dim nameToSearch As String
Dim token As CancellationToken
Dim results As New List(Of String)
Dim m_lock As Object
Dim count As Integer
Dim addresses() As String
Shared Sub Main()
Dim downloader As New WebDataDownLoader()
downloader.addresses = {"http://www.msnbc.com", "http://www.yahoo.com", _
"http://www.nytimes.com", "http://www.washingtonpost.com", _
"http://www.latimes.com", "http://www.newsday.com"}
Dim cts As New CancellationTokenSource()
' Create a UI thread from which to cancel the entire operation
Task.Factory.StartNew(Sub()
Console.WriteLine("Press c to cancel")
If Console.ReadKey().KeyChar = "c"c Then
cts.Cancel()
End If
End Sub)
' Using a neutral search term that is sure to get some hits on English web sites.
' Please substitute your favorite search term.
downloader.nameToSearch = "the"
Dim webTask As Task(Of String()) = downloader.GetWordCounts(downloader.addresses, downloader.nameToSearch, cts.Token)
' Do some other work here unless the method has already completed.
If (webTask.IsCompleted = False) Then
' Simulate some work
Thread.SpinWait(5000000)
End If
Dim results As String() = Nothing
Try
results = webTask.Result
Catch ae As AggregateException
For Each ex As Exception In ae.InnerExceptions
If (TypeOf (ex) Is OperationCanceledException) Then
Dim oce As OperationCanceledException = CType(ex, OperationCanceledException)
If oce.CancellationToken = cts.Token Then
Console.WriteLine("Operation canceled by user.")
End If
Else
Console.WriteLine(ex.Message)
End If
Next
Finally
cts.Dispose()
End Try
If (Not results Is Nothing) Then
For Each item As String In results
Console.WriteLine(item)
Next
End If
Console.WriteLine("Press any key to exit")
Console.ReadKey()
End Sub
Public Function GetWordCounts(ByVal urls() As String, ByVal str As String, ByVal token As CancellationToken) As Task(Of String())
Dim webClients() As WebClient
ReDim webClients(urls.Length)
m_lock = New Object()
' If the user cancels the CancellationToken, then we can use the
' WebClient's ability to cancel its own async operations.
token.Register(Sub()
For Each wc As WebClient In webClients
If Not wc Is Nothing Then
wc.CancelAsync()
End If
Next
End Sub)
For i As Integer = 0 To urls.Length - 1
webClients(i) = New WebClient()
' Specify the callback for the DownloadStringCompleted
' event that will be raised by this WebClient instance.
AddHandler webClients(i).DownloadStringCompleted, AddressOf WebEventHandler
Dim address As Uri = Nothing
Try
address = New Uri(urls(i))
' Pass the address, and also use it for the userToken
' to identify the page when the delegate is invoked.
webClients(i).DownloadStringAsync(address, address)
Catch ex As UriFormatException
tcs.TrySetException(ex)
Return tcs.Task
End Try
Next
' Return the underlying Task. The client code
' waits on the Result property, and handles exceptions
' in the try-catch block there.
Return tcs.Task
End Function
Public Sub WebEventHandler(ByVal sender As Object, ByVal args As DownloadStringCompletedEventArgs)
If args.Cancelled = True Then
tcs.TrySetCanceled()
Return
ElseIf Not args.Error Is Nothing Then
tcs.TrySetException(args.Error)
Return
Else
' Split the string into an array of words,
' then count the number of elements that match
' the search term.
Dim words() As String = args.Result.Split(" "c)
Dim NAME As String = nameToSearch.ToUpper()
Dim nameCount = (From word In words.AsParallel()
Where word.ToUpper().Contains(NAME)
Select word).Count()
' Associate the results with the url, and add new string to the array that
' the underlying Task object will return in its Result property.
results.Add(String.Format("{0} has {1} instances of {2}", args.UserState, nameCount, nameToSearch))
End If
SyncLock (m_lock)
count = count + 1
If (count = addresses.Length) Then
tcs.TrySetResult(results.ToArray())
End If
End SyncLock
End Sub
'</snippet08>
End Class
'<snippet09>
Class Calculator
Public Function BeginCalculate(ByVal decimalPlaces As Integer, ByVal ac As AsyncCallback, ByVal state As Object) As IAsyncResult
Console.WriteLine("Calling BeginCalculate on thread {0}", Thread.CurrentThread.ManagedThreadId)
Dim myTask = Task(Of String).Factory.StartNew(Function(obj) Compute(decimalPlaces), state)
myTask.ContinueWith(Sub(antecedent) ac(myTask))
End Function
Private Function Compute(ByVal decimalPlaces As Integer)
Console.WriteLine("Calling compute on thread {0}", Thread.CurrentThread.ManagedThreadId)
' Simulating some heavy work.
Thread.SpinWait(500000000)
' Actual implementation left as exercise for the reader.
' Several examples are available on the Web.
Return "3.14159265358979323846264338327950288"
End Function
Public Function EndCalculate(ByVal ar As IAsyncResult) As String
Console.WriteLine("Calling EndCalculate on thread {0}", Thread.CurrentThread.ManagedThreadId)
Return CType(ar, Task(Of String)).Result
End Function
End Class
Class CalculatorClient
Shared decimalPlaces As Integer
Shared Sub Main()
Dim calc As New Calculator
Dim places As Integer = 35
Dim callback As New AsyncCallback(AddressOf PrintResult)
Dim ar As IAsyncResult = calc.BeginCalculate(places, callback, calc)
' Do some work on this thread while the calculator is busy.
Console.WriteLine("Working...")
Thread.SpinWait(500000)
Console.ReadLine()
End Sub
Public Shared Sub PrintResult(ByVal result As IAsyncResult)
Dim c As Calculator = CType(result.AsyncState, Calculator)
Dim piString As String = c.EndCalculate(result)
Console.WriteLine("Calling PrintResult on thread {0}; result = {1}",
Thread.CurrentThread.ManagedThreadId, piString)
End Sub
End Class
'</snippet09>
Class FileStreamDemo
Shared Sub Main()
Dim fsd As New FileStreamDemo()
fsd.ShowCallingFromAsync()
End Sub
'<snippet03>
Const MAX_FILE_SIZE As Integer = 14000000
Shared Function GetFileStringAsync(ByVal path As String) As Task(Of String)
Dim fi As New FileInfo(path)
Dim data(fi.Length - 1) As Byte
Dim fs As FileStream = New FileStream(path, FileMode.Open, FileAccess.Read, FileShare.Read, data.Length, True)
' Task(Of Integer) returns the number of bytes read
Dim myTask As Task(Of Integer) = Task(Of Integer).Factory.FromAsync(
AddressOf fs.BeginRead, AddressOf fs.EndRead, data, 0, data.Length, Nothing)
' It is possible to do other work here while waiting
' for the antecedent task to complete.
' ...
' Add the continuation, which returns a Task<string>.
Return myTask.ContinueWith(Function(antecedent)
fs.Close()
If (antecedent.Result < 100) Then
Return "Data is too small to bother with."
End If
' If we did not receive the entire file, the end of the
' data buffer will contain garbage.
If (antecedent.Result < data.Length) Then
Array.Resize(data, antecedent.Result)
End If
' Will be returned in the Result property of the Task<string>
' at some future point after the asynchronous file I/O operation completes.
Return New UTF8Encoding().GetString(data)
End Function)
End Function
'</snippet03>
Public Sub ShowCallingFromAsync()
Dim path As String = "\\docbuild2\public\Main\Logs\DllDiffReport\DllDiffReport_BetweenInBuildAndInPublicShare.html"
'<snippet04>
Dim myTask As Task(Of String) = GetFileStringAsync(path)
' Do some other work
' ...
Try
Console.WriteLine(myTask.Result.Substring(0, 500))
Catch ex As AggregateException
Console.WriteLine(ex.InnerException.Message)
End Try
'</snippet04>
Console.WriteLine("Press Enter to exit.")
Console.ReadLine()
End Sub
'<snippet05>
Public Function GetFileStringAsync2(ByVal path As String) As Task(Of String)
Dim fi = New FileInfo(path)
Dim data(fi.Length - 1) As Byte
Dim state As New MyCustomState()
Dim fs As New FileStream(path, FileMode.Open, FileAccess.Read, FileShare.Read, data.Length, True)
' We still pass null for the last parameter because
' the state variable is visible to the continuation delegate.
Dim myTask As Task(Of Integer) = Task(Of Integer).Factory.FromAsync(
AddressOf fs.BeginRead, AddressOf fs.EndRead, data, 0, data.Length, Nothing)
Return myTask.ContinueWith(Function(antecedent)
fs.Close()
' Capture custom state data directly in the user delegate.
' No need to pass it through the FromAsync method.
If (state.StateData.Contains("New York, New York")) Then
Return "Start spreading the news!"
End If
' If we did not receive the entire file, the end of the
' data buffer will contain garbage.
If (antecedent.Result < data.Length) Then
Array.Resize(data, antecedent.Result)
End If
'/ Will be returned in the Result property of the Task<string>
'/ at some future point after the asynchronous file I/O operation completes.
Return New UTF8Encoding().GetString(data)
End Function)
End Function
'</snippet05>
'<snippet06>
Public Function GetMultiFileData(ByVal filesToRead As String()) As Task(Of String)
Dim fs As FileStream
Dim tasks(filesToRead.Length - 1) As Task(Of String)
Dim fileData() As Byte = Nothing
For i As Integer = 0 To filesToRead.Length
fileData(&H1000) = New Byte()
fs = New FileStream(filesToRead(i), FileMode.Open, FileAccess.Read, FileShare.Read, fileData.Length, True)
' By adding the continuation here, the
' Result of each task will be a string.
tasks(i) = Task(Of Integer).Factory.FromAsync(AddressOf fs.BeginRead,
AddressOf fs.EndRead,
fileData,
0,
fileData.Length,
Nothing).
ContinueWith(Function(antecedent)
fs.Close()
'If we did not receive the entire file, the end of the
' data buffer will contain garbage.
If (antecedent.Result < fileData.Length) Then
ReDim Preserve fileData(antecedent.Result)
End If
'Will be returned in the Result property of the Task<string>
' at some future point after the asynchronous file I/O operation completes.
Return New UTF8Encoding().GetString(fileData)
End Function)
Next
Return Task(Of String).Factory.ContinueWhenAll(tasks, Function(data)
' Propagate all exceptions and mark all faulted tasks as observed.
Task.WaitAll(data)
' Combine the results from all tasks.
Dim sb As New StringBuilder()
For Each t As Task(Of String) In data
sb.Append(t.Result)
Next
' Final result to be returned eventually on the calling thread.
Return sb.ToString()
End Function)
End Function
'</snippet06>
Class MyCustomState
Public StateData As String
Public Sub New()
StateData = "Hello"
End Sub
End Class
End Class
End ModuleProvide custom state data
In typical System.IAsyncResult operations, if your System.AsyncCallback delegate requires some custom state data, you have to pass it in through the last parameter in the Begin method, so that the data can be packaged into the System.IAsyncResult object that is eventually passed to the callback method. This is typically not required when the FromAsync methods are used. If the custom data is known to the continuation, then it can be captured directly in the continuation delegate. The following example resembles the previous example, but instead of examining the Result property of the antecedent, the continuation examines the custom state data that is directly accessible to the user delegate of the continuation.
sample · csharpsamples/snippets/csharp/VS_Snippets_Misc/fromasync/cs/fromasync.cs05
using System;
using System.Collections.Concurrent;
using System.Collections.Generic;
using System.Diagnostics;
using System.IO;
using System.Linq;
using System.Text;
using System.Threading;
using System.Threading.Tasks;
using System.Net;
namespace specialNamespaceForOneMethodSignature
{
using System;
class Task<TResult>
{
public TResult TValue;
}
class Dummy <TResult>
{
// <snippet01>
public Task<TResult> FromAsync<TArg1, TArg2, TArg3>(
Func<TArg1, TArg2, TArg3, AsyncCallback, object, IAsyncResult> beginMethod, //BeginRead
Func<IAsyncResult, TResult> endMethod, //EndRead
TArg1 arg1, // the byte[] buffer
TArg2 arg2, // the offset in arg1 at which to start writing data
TArg3 arg3, // the maximum number of bytes to read
object state // optional state information
)
//</snippet01>
{ return new Task<TResult>(); }
}
}
namespace APM_Task
{
class TestFileStreamNaive
{
//<snippet02>
public string GetFileData(string path)
{
FileInfo fi = new FileInfo(path);
byte[] data = new byte[fi.Length];
FileStream fs;
// a using statement is ok here because we Wait before returning
// and will be done with the filestream.
using (fs = new FileStream(path, FileMode.Open, FileAccess.Read, FileShare.Read, data.Length, true))
{
//Task<int> returns the number of bytes read
Task<int> task = Task<int>.Factory.FromAsync(
fs.BeginRead, fs.EndRead, data, 0, data.Length, null);
task.Wait();
return new UTF8Encoding().GetString(data);
}
}
//</snippet02>
static void Main()
{
TestFileStreamNaive instance = new TestFileStreamNaive();
string s = instance.GetFileData("testfile.txt");
}
}
class AsyncResult : IAsyncResult
{
public AsyncResult() { }
public object AsyncState
{
get { return "Hello from a parallel universe."; }
}
public WaitHandle AsyncWaitHandle
{
get { throw new NotImplementedException(); }
}
public bool CompletedSynchronously
{
get { throw new NotImplementedException(); }
}
public bool IsCompleted
{
get { throw new NotImplementedException(); }
}
static IAsyncResult DoSomethingAsynchronously()
{
return new AsyncResult();
}
//<snippet07>
static Task<String> ReturnTaskFromAsyncResult()
{
IAsyncResult ar = DoSomethingAsynchronously();
Task<String> t = Task<string>.Factory.FromAsync(ar, _ =>
{
return (string)ar.AsyncState;
});
return t;
}
//</snippet07>
}
//<snippet08>
class WebDataDownloader
{
static void Main()
{
WebDataDownloader downloader = new WebDataDownloader();
string[] addresses = { "http://www.msnbc.com", "http://www.yahoo.com",
"http://www.nytimes.com", "http://www.washingtonpost.com",
"http://www.latimes.com", "http://www.newsday.com" };
CancellationTokenSource cts = new CancellationTokenSource();
// Create a UI thread from which to cancel the entire operation
Task.Factory.StartNew(() =>
{
Console.WriteLine("Press c to cancel");
if (Console.ReadKey().KeyChar == 'c')
cts.Cancel();
});
// Using a neutral search term that is sure to get some hits.
Task<string[]> webTask = downloader.GetWordCounts(addresses, "the", cts.Token);
// Do some other work here unless the method has already completed.
if (!webTask.IsCompleted)
{
// Simulate some work.
Thread.SpinWait(5000000);
}
string[] results = null;
try
{
results = webTask.Result;
}
catch (AggregateException e)
{
foreach (var ex in e.InnerExceptions)
{
OperationCanceledException oce = ex as OperationCanceledException;
if (oce != null)
{
if (oce.CancellationToken == cts.Token)
{
Console.WriteLine("Operation canceled by user.");
}
}
else
{
Console.WriteLine(ex.Message);
}
}
}
finally
{
cts.Dispose();
}
if (results != null)
{
foreach (var item in results)
Console.WriteLine(item);
}
Console.ReadKey();
}
Task<string[]> GetWordCounts(string[] urls, string name, CancellationToken token)
{
TaskCompletionSource<string[]> tcs = new TaskCompletionSource<string[]>();
WebClient[] webClients = new WebClient[urls.Length];
// If the user cancels the CancellationToken, then we can use the
// WebClient's ability to cancel its own async operations.
token.Register(() =>
{
foreach (var wc in webClients)
{
if (wc != null)
wc.CancelAsync();
}
});
object m_lock = new object();
int count = 0;
List<string> results = new List<string>();
for (int i = 0; i < urls.Length; i++)
{
webClients[i] = new WebClient();
#region callback
// Specify the callback for the DownloadStringCompleted
// event that will be raised by this WebClient instance.
webClients[i].DownloadStringCompleted += (obj, args) =>
{
if (args.Cancelled == true)
{
tcs.TrySetCanceled();
return;
}
else if (args.Error != null)
{
// Pass through to the underlying Task
// any exceptions thrown by the WebClient
// during the asynchronous operation.
tcs.TrySetException(args.Error);
return;
}
else
{
// Split the string into an array of words,
// then count the number of elements that match
// the search term.
string[] words = null;
words = args.Result.Split(' ');
string NAME = name.ToUpper();
int nameCount = (from word in words.AsParallel()
where word.ToUpper().Contains(NAME)
select word)
.Count();
// Associate the results with the url, and add new string to the array that
// the underlying Task object will return in its Result property.
results.Add(String.Format("{0} has {1} instances of {2}", args.UserState, nameCount, name));
}
// If this is the last async operation to complete,
// then set the Result property on the underlying Task.
lock (m_lock)
{
count++;
if (count == urls.Length)
{
tcs.TrySetResult(results.ToArray());
}
}
};
#endregion
// Call DownloadStringAsync for each URL.
Uri address = null;
try
{
address = new Uri(urls[i]);
// Pass the address, and also use it for the userToken
// to identify the page when the delegate is invoked.
webClients[i].DownloadStringAsync(address, address);
}
catch (UriFormatException ex)
{
// Abandon the entire operation if one url is malformed.
// Other actions are possible here.
tcs.TrySetException(ex);
return tcs.Task;
}
}
// Return the underlying Task. The client code
// waits on the Result property, and handles exceptions
// in the try-catch block there.
return tcs.Task;
}
//</snippet08>
}
#region snippet09
class Calculator
{
public IAsyncResult BeginCalculate(int decimalPlaces, AsyncCallback ac, object state)
{
Console.WriteLine($"Calling BeginCalculate on thread {Thread.CurrentThread.ManagedThreadId}");
Task<string> f = Task<string>.Factory.StartNew(_ => Compute(decimalPlaces), state);
if (ac != null) f.ContinueWith((res) => ac(f));
return f;
}
public string Compute(int numPlaces)
{
Console.WriteLine($"Calling compute on thread {Thread.CurrentThread.ManagedThreadId}");
// Simulating some heavy work.
Thread.SpinWait(500000000);
// Actual implementation left as exercise for the reader.
// Several examples are available on the Web.
return "3.14159265358979323846264338327950288";
}
public string EndCalculate(IAsyncResult ar)
{
Console.WriteLine($"Calling EndCalculate on thread {Thread.CurrentThread.ManagedThreadId}");
return ((Task<string>)ar).Result;
}
}
public class CalculatorClient
{
static int decimalPlaces = 12;
public static void Main()
{
Calculator calc = new Calculator();
int places = 35;
AsyncCallback callBack = new AsyncCallback(PrintResult);
IAsyncResult ar = calc.BeginCalculate(places, callBack, calc);
// Do some work on this thread while the calculator is busy.
Console.WriteLine("Working...");
Thread.SpinWait(500000);
Console.ReadLine();
}
public static void PrintResult(IAsyncResult result)
{
Calculator c = (Calculator)result.AsyncState;
string piString = c.EndCalculate(result);
Console.WriteLine($"Calling PrintResult on thread {Thread.CurrentThread.ManagedThreadId}; result = {piString}");
}
}
#endregion
} //end APM_Task namespace
class FileStreamDemo
{
static void Main()
{
FileStreamDemo fsd = new FileStreamDemo();
// var task = fsd.GetMultiFileData(new string[1]);
fsd.ShowCallingFromAsync();
// fsd.ShowCallingFromAsyncFileData();
// fsd.ProcessFilesAsync();
// task.Wait();
// Console.WriteLine(task.Result);
Console.WriteLine("press any key");
Console.ReadLine();
}
//<snippet03>
const int MAX_FILE_SIZE = 14000000;
public static Task<string> GetFileStringAsync(string path)
{
FileInfo fi = new FileInfo(path);
byte[] data = null;
data = new byte[fi.Length];
FileStream fs = new FileStream(path, FileMode.Open, FileAccess.Read, FileShare.Read, data.Length, true);
//Task<int> returns the number of bytes read
Task<int> task = Task<int>.Factory.FromAsync(
fs.BeginRead, fs.EndRead, data, 0, data.Length, null);
// It is possible to do other work here while waiting
// for the antecedent task to complete.
// ...
// Add the continuation, which returns a Task<string>.
return task.ContinueWith((antecedent) =>
{
fs.Close();
// Result = "number of bytes read" (if we need it.)
if (antecedent.Result < 100)
{
return "Data is too small to bother with.";
}
else
{
// If we did not receive the entire file, the end of the
// data buffer will contain garbage.
if (antecedent.Result < data.Length)
Array.Resize(ref data, antecedent.Result);
// Will be returned in the Result property of the Task<string>
// at some future point after the asynchronous file I/O operation completes.
return new UTF8Encoding().GetString(data);
}
});
}
//</snippet03>
void ShowCallingFromAsync()
{
string path = @"\\docbuild2\public\Main\Logs\DllDiffReport\DllDiffReport_BetweenInBuildAndInProduct.html";
//<snippet04>
Task<string> t = GetFileStringAsync(path);
// Do some other work:
// ...
try
{
Console.WriteLine(t.Result.Substring(0, 500));
}
catch (AggregateException ae)
{
Console.WriteLine(ae.InnerException.Message);
}
//</snippet04>
Console.ReadLine();
}
//not used???
//<snippet12>
public static Task<int> GetFileDataAsync(string path, ref byte[] data)
{
// Error handling omitted for brevity...
FileInfo fi = new FileInfo(path);
data = new byte[fi.Length];
FileStream fs = new FileStream(path, FileMode.Open, FileAccess.Read, FileShare.Read, data.Length, true);
// Task<int> returns the number of bytes read
// Pass FileStream in AsyncState parameter in order to close it from the call site.
return Task<int>.Factory.FromAsync(
fs.BeginRead, fs.EndRead, data, 0, data.Length, fs);
}
//</snippet12>
void ShowCallingFromAsyncFileData()
{
//<snippet13>
string path = @"\\remoteComputer\filename.txt";
byte[] buffer = null;
Task<int> t = GetFileDataAsync(path, ref buffer);
// Can do some other work here:
// ...
for(int i = 0; i < 10; i++)
Console.Write("Working... ");
var result =
t.ContinueWith((antecedent) =>
{
// Error handling omitted...
return new UTF8Encoding().GetString(buffer);
});
// Can also do some other work here:
// ...
for (int i = 0; i < 10; i++)
Console.Write("Working more... ");
try
{
t.Wait();
Console.WriteLine(result.Result.Substring(0, 50));
}
catch (AggregateException ae)
{
Console.WriteLine(ae.InnerException.Message);
}
//</snippet13>
Console.ReadLine();
}
// nested dummy class for snippet0 5 below
class MyCustomState
{
public string StateData { get; set; }
public MyCustomState() { StateData = "Hello"; }
}
private MyCustomState GetCustomState()
{
return new MyCustomState();
}
//<snippet05>
public Task<string> GetFileStringAsync2(string path)
{
FileInfo fi = new FileInfo(path);
byte[] data = new byte[fi.Length];
MyCustomState state = GetCustomState();
FileStream fs = new FileStream(path, FileMode.Open, FileAccess.Read, FileShare.Read, data.Length, true);
// We still pass null for the last parameter because
// the state variable is visible to the continuation delegate.
Task<int> task = Task<int>.Factory.FromAsync(
fs.BeginRead, fs.EndRead, data, 0, data.Length, null);
return task.ContinueWith((antecedent) =>
{
// It is safe to close the filestream now.
fs.Close();
// Capture custom state data directly in the user delegate.
// No need to pass it through the FromAsync method.
if (state.StateData.Contains("New York, New York"))
{
return "Start spreading the news!";
}
else
{
// If we did not receive the entire file, the end of the
// data buffer will contain garbage.
if (antecedent.Result < data.Length)
Array.Resize(ref data, antecedent.Result);
// Will be returned in the Result property of the Task<string>
// at some future point after the asynchronous file I/O operation completes.
return new UTF8Encoding().GetString(data);
}
});
}
//</snippet05>
string[] GetFilesToRead()
{
return new string[3] { "test.txt", "test1.txt", "test2.txt" };
}
//<snippet06>
public Task<string> GetMultiFileData(string[] filesToRead)
{
FileStream fs;
Task<string>[] tasks = new Task<string>[filesToRead.Length];
byte[] fileData = null;
for (int i = 0; i < filesToRead.Length; i++)
{
fileData = new byte[0x1000];
fs = new FileStream(filesToRead[i], FileMode.Open, FileAccess.Read, FileShare.Read, fileData.Length, true);
// By adding the continuation here, the
// Result of each task will be a string.
tasks[i] = Task<int>.Factory.FromAsync(
fs.BeginRead, fs.EndRead, fileData, 0, fileData.Length, null)
.ContinueWith((antecedent) =>
{
fs.Close();
// If we did not receive the entire file, the end of the
// data buffer will contain garbage.
if (antecedent.Result < fileData.Length)
Array.Resize(ref fileData, antecedent.Result);
// Will be returned in the Result property of the Task<string>
// at some future point after the asynchronous file I/O operation completes.
return new UTF8Encoding().GetString(fileData);
});
}
// Wait for all tasks to complete.
return Task<string>.Factory.ContinueWhenAll(tasks, (data) =>
{
// Propagate all exceptions and mark all faulted tasks as observed.
Task.WaitAll(data);
// Combine the results from all tasks.
StringBuilder sb = new StringBuilder();
foreach (var t in data)
{
sb.Append(t.Result);
}
// Final result to be returned eventually on the calling thread.
return sb.ToString();
});
}
//</snippet06>
public string ProcessData(Task[] arr)
{
return "processed";
}
//<snippet11>
void ProcessFilesAsync()
{
string[] files = Directory.GetFiles(@"\\remoteComputer\folderName\", "*.*", SearchOption.AllDirectories);
CancellationTokenSource cts = new CancellationTokenSource();
List<Task<string>> tasks = new List<Task<string>>();
foreach (var file in files)
{
Task<string> t = null;
try
{
t = GetFileStringAsync3(file, cts.Token);
}
catch
{
Console.WriteLine($"Argument exception on {file}");
continue;
}
t.ContinueWith((antecedent) => ProcessFileData(antecedent.Result));
tasks.Add(t);
}
Console.WriteLine("All tasks have been added.");
// Do some work here.
try
{
Task.WaitAll(tasks.ToArray());
Console.WriteLine("All tasks have completed.");
}
catch (AggregateException ae)
{
foreach (var ex in ae.InnerExceptions)
Console.WriteLine(ex.Message);
}
finally
{
cts.Dispose();
}
// If needed, perform a final step after all tasks have completed.
Task.Factory.ContinueWhenAll(tasks.ToArray(), (arr) =>
{
foreach (var t in arr)
{
CompareFileData(t.Result);
}
});
}
public Task<string> GetFileStringAsync3(string path, CancellationToken token)
{
if (!File.Exists(path))
{
throw new FileNotFoundException(String.Format("Could not find {0}", path));
}
FileInfo fi = new FileInfo(path);
byte[] data = null;
if (fi.Length < MAX_FILE_SIZE && fi.Length > 0)
{
data = new byte[fi.Length];
}
else
{
throw new ArgumentException(String.Format("{0} is too big to load!", path));
}
FileStream fs = new FileStream(path, FileMode.Open, FileAccess.Read, FileShare.Read, data.Length, true);
// We still pass null for the last parameter because
// the state variable is visible to the continuation delegate.
Task<int> task = Task<int>.Factory.FromAsync(
fs.BeginRead, fs.EndRead, data, 0, data.Length, null);
return task.ContinueWith((antecedent) =>
{
fs.Close();
// If we did not receive the entire file, the end of the
// data buffer will contain garbage.
if (antecedent.Result < data.Length)
Array.Resize(ref data, antecedent.Result);
// Will be returned in the Result property of the Task<string>
// at some future point after the asynchronous file I/O operation completes.
return new UTF8Encoding().GetString(data);
});
}
string ProcessFileData(string data)
{
string s = data.Substring(0, 80);
Console.WriteLine(s);
return s;
}
string CompareFileData(string s)
{
return "compare results";
}
//</snippet11>
}sample · vbsamples/snippets/visualbasic/VS_Snippets_Misc/fromasync/vb/module1.vb05
Imports System.Collections.Generic
Imports System.IO
Imports System.Net
Imports System.Text
Imports System.Threading
Imports System.Threading.Tasks
Namespace specialNamespaceForOneMethodSignature
Class Task(Of TResult)
Public TValue As TResult
End Class
Class Dummy(Of TResult)
'<snippet01>
Public Function FromAsync(Of TArg1, TArg2, TArg3)(
ByVal beginMethod As Func(Of TArg1, TArg2, TArg3, AsyncCallback, Object, IAsyncResult),
ByVal endMethod As Func(Of IAsyncResult, TResult),
ByVal dataBuffer As TArg1,
ByVal byteOffsetToStartAt As TArg2,
ByVal maxBytesToRead As TArg3,
ByVal stateInfo As Object)
'</snippet01>
Return New Task(Of TResult)
End Function
End Class
End Namespace
Module Module1
Class AsyncResult
Public Sub New()
End Sub
'<snippet07>
Shared Function ReturnTaskFromAsyncResult() As Task(Of String)
Dim ar As IAsyncResult = DoSomethingAsynchronously()
Dim t As Task(Of String) = Task(Of String).Factory.FromAsync(ar, Function(res) CStr(res.AsyncState))
Return t
End Function
'</snippet07>
Private Shared Function DoSomethingAsynchronously() As IAsyncResult
Throw New NotImplementedException
End Function
End Class
'<snippet08>
Class WebDataDownLoader
Dim tcs As New TaskCompletionSource(Of String())
Dim nameToSearch As String
Dim token As CancellationToken
Dim results As New List(Of String)
Dim m_lock As Object
Dim count As Integer
Dim addresses() As String
Shared Sub Main()
Dim downloader As New WebDataDownLoader()
downloader.addresses = {"http://www.msnbc.com", "http://www.yahoo.com", _
"http://www.nytimes.com", "http://www.washingtonpost.com", _
"http://www.latimes.com", "http://www.newsday.com"}
Dim cts As New CancellationTokenSource()
' Create a UI thread from which to cancel the entire operation
Task.Factory.StartNew(Sub()
Console.WriteLine("Press c to cancel")
If Console.ReadKey().KeyChar = "c"c Then
cts.Cancel()
End If
End Sub)
' Using a neutral search term that is sure to get some hits on English web sites.
' Please substitute your favorite search term.
downloader.nameToSearch = "the"
Dim webTask As Task(Of String()) = downloader.GetWordCounts(downloader.addresses, downloader.nameToSearch, cts.Token)
' Do some other work here unless the method has already completed.
If (webTask.IsCompleted = False) Then
' Simulate some work
Thread.SpinWait(5000000)
End If
Dim results As String() = Nothing
Try
results = webTask.Result
Catch ae As AggregateException
For Each ex As Exception In ae.InnerExceptions
If (TypeOf (ex) Is OperationCanceledException) Then
Dim oce As OperationCanceledException = CType(ex, OperationCanceledException)
If oce.CancellationToken = cts.Token Then
Console.WriteLine("Operation canceled by user.")
End If
Else
Console.WriteLine(ex.Message)
End If
Next
Finally
cts.Dispose()
End Try
If (Not results Is Nothing) Then
For Each item As String In results
Console.WriteLine(item)
Next
End If
Console.WriteLine("Press any key to exit")
Console.ReadKey()
End Sub
Public Function GetWordCounts(ByVal urls() As String, ByVal str As String, ByVal token As CancellationToken) As Task(Of String())
Dim webClients() As WebClient
ReDim webClients(urls.Length)
m_lock = New Object()
' If the user cancels the CancellationToken, then we can use the
' WebClient's ability to cancel its own async operations.
token.Register(Sub()
For Each wc As WebClient In webClients
If Not wc Is Nothing Then
wc.CancelAsync()
End If
Next
End Sub)
For i As Integer = 0 To urls.Length - 1
webClients(i) = New WebClient()
' Specify the callback for the DownloadStringCompleted
' event that will be raised by this WebClient instance.
AddHandler webClients(i).DownloadStringCompleted, AddressOf WebEventHandler
Dim address As Uri = Nothing
Try
address = New Uri(urls(i))
' Pass the address, and also use it for the userToken
' to identify the page when the delegate is invoked.
webClients(i).DownloadStringAsync(address, address)
Catch ex As UriFormatException
tcs.TrySetException(ex)
Return tcs.Task
End Try
Next
' Return the underlying Task. The client code
' waits on the Result property, and handles exceptions
' in the try-catch block there.
Return tcs.Task
End Function
Public Sub WebEventHandler(ByVal sender As Object, ByVal args As DownloadStringCompletedEventArgs)
If args.Cancelled = True Then
tcs.TrySetCanceled()
Return
ElseIf Not args.Error Is Nothing Then
tcs.TrySetException(args.Error)
Return
Else
' Split the string into an array of words,
' then count the number of elements that match
' the search term.
Dim words() As String = args.Result.Split(" "c)
Dim NAME As String = nameToSearch.ToUpper()
Dim nameCount = (From word In words.AsParallel()
Where word.ToUpper().Contains(NAME)
Select word).Count()
' Associate the results with the url, and add new string to the array that
' the underlying Task object will return in its Result property.
results.Add(String.Format("{0} has {1} instances of {2}", args.UserState, nameCount, nameToSearch))
End If
SyncLock (m_lock)
count = count + 1
If (count = addresses.Length) Then
tcs.TrySetResult(results.ToArray())
End If
End SyncLock
End Sub
'</snippet08>
End Class
'<snippet09>
Class Calculator
Public Function BeginCalculate(ByVal decimalPlaces As Integer, ByVal ac As AsyncCallback, ByVal state As Object) As IAsyncResult
Console.WriteLine("Calling BeginCalculate on thread {0}", Thread.CurrentThread.ManagedThreadId)
Dim myTask = Task(Of String).Factory.StartNew(Function(obj) Compute(decimalPlaces), state)
myTask.ContinueWith(Sub(antecedent) ac(myTask))
End Function
Private Function Compute(ByVal decimalPlaces As Integer)
Console.WriteLine("Calling compute on thread {0}", Thread.CurrentThread.ManagedThreadId)
' Simulating some heavy work.
Thread.SpinWait(500000000)
' Actual implementation left as exercise for the reader.
' Several examples are available on the Web.
Return "3.14159265358979323846264338327950288"
End Function
Public Function EndCalculate(ByVal ar As IAsyncResult) As String
Console.WriteLine("Calling EndCalculate on thread {0}", Thread.CurrentThread.ManagedThreadId)
Return CType(ar, Task(Of String)).Result
End Function
End Class
Class CalculatorClient
Shared decimalPlaces As Integer
Shared Sub Main()
Dim calc As New Calculator
Dim places As Integer = 35
Dim callback As New AsyncCallback(AddressOf PrintResult)
Dim ar As IAsyncResult = calc.BeginCalculate(places, callback, calc)
' Do some work on this thread while the calculator is busy.
Console.WriteLine("Working...")
Thread.SpinWait(500000)
Console.ReadLine()
End Sub
Public Shared Sub PrintResult(ByVal result As IAsyncResult)
Dim c As Calculator = CType(result.AsyncState, Calculator)
Dim piString As String = c.EndCalculate(result)
Console.WriteLine("Calling PrintResult on thread {0}; result = {1}",
Thread.CurrentThread.ManagedThreadId, piString)
End Sub
End Class
'</snippet09>
Class FileStreamDemo
Shared Sub Main()
Dim fsd As New FileStreamDemo()
fsd.ShowCallingFromAsync()
End Sub
'<snippet03>
Const MAX_FILE_SIZE As Integer = 14000000
Shared Function GetFileStringAsync(ByVal path As String) As Task(Of String)
Dim fi As New FileInfo(path)
Dim data(fi.Length - 1) As Byte
Dim fs As FileStream = New FileStream(path, FileMode.Open, FileAccess.Read, FileShare.Read, data.Length, True)
' Task(Of Integer) returns the number of bytes read
Dim myTask As Task(Of Integer) = Task(Of Integer).Factory.FromAsync(
AddressOf fs.BeginRead, AddressOf fs.EndRead, data, 0, data.Length, Nothing)
' It is possible to do other work here while waiting
' for the antecedent task to complete.
' ...
' Add the continuation, which returns a Task<string>.
Return myTask.ContinueWith(Function(antecedent)
fs.Close()
If (antecedent.Result < 100) Then
Return "Data is too small to bother with."
End If
' If we did not receive the entire file, the end of the
' data buffer will contain garbage.
If (antecedent.Result < data.Length) Then
Array.Resize(data, antecedent.Result)
End If
' Will be returned in the Result property of the Task<string>
' at some future point after the asynchronous file I/O operation completes.
Return New UTF8Encoding().GetString(data)
End Function)
End Function
'</snippet03>
Public Sub ShowCallingFromAsync()
Dim path As String = "\\docbuild2\public\Main\Logs\DllDiffReport\DllDiffReport_BetweenInBuildAndInPublicShare.html"
'<snippet04>
Dim myTask As Task(Of String) = GetFileStringAsync(path)
' Do some other work
' ...
Try
Console.WriteLine(myTask.Result.Substring(0, 500))
Catch ex As AggregateException
Console.WriteLine(ex.InnerException.Message)
End Try
'</snippet04>
Console.WriteLine("Press Enter to exit.")
Console.ReadLine()
End Sub
'<snippet05>
Public Function GetFileStringAsync2(ByVal path As String) As Task(Of String)
Dim fi = New FileInfo(path)
Dim data(fi.Length - 1) As Byte
Dim state As New MyCustomState()
Dim fs As New FileStream(path, FileMode.Open, FileAccess.Read, FileShare.Read, data.Length, True)
' We still pass null for the last parameter because
' the state variable is visible to the continuation delegate.
Dim myTask As Task(Of Integer) = Task(Of Integer).Factory.FromAsync(
AddressOf fs.BeginRead, AddressOf fs.EndRead, data, 0, data.Length, Nothing)
Return myTask.ContinueWith(Function(antecedent)
fs.Close()
' Capture custom state data directly in the user delegate.
' No need to pass it through the FromAsync method.
If (state.StateData.Contains("New York, New York")) Then
Return "Start spreading the news!"
End If
' If we did not receive the entire file, the end of the
' data buffer will contain garbage.
If (antecedent.Result < data.Length) Then
Array.Resize(data, antecedent.Result)
End If
'/ Will be returned in the Result property of the Task<string>
'/ at some future point after the asynchronous file I/O operation completes.
Return New UTF8Encoding().GetString(data)
End Function)
End Function
'</snippet05>
'<snippet06>
Public Function GetMultiFileData(ByVal filesToRead As String()) As Task(Of String)
Dim fs As FileStream
Dim tasks(filesToRead.Length - 1) As Task(Of String)
Dim fileData() As Byte = Nothing
For i As Integer = 0 To filesToRead.Length
fileData(&H1000) = New Byte()
fs = New FileStream(filesToRead(i), FileMode.Open, FileAccess.Read, FileShare.Read, fileData.Length, True)
' By adding the continuation here, the
' Result of each task will be a string.
tasks(i) = Task(Of Integer).Factory.FromAsync(AddressOf fs.BeginRead,
AddressOf fs.EndRead,
fileData,
0,
fileData.Length,
Nothing).
ContinueWith(Function(antecedent)
fs.Close()
'If we did not receive the entire file, the end of the
' data buffer will contain garbage.
If (antecedent.Result < fileData.Length) Then
ReDim Preserve fileData(antecedent.Result)
End If
'Will be returned in the Result property of the Task<string>
' at some future point after the asynchronous file I/O operation completes.
Return New UTF8Encoding().GetString(fileData)
End Function)
Next
Return Task(Of String).Factory.ContinueWhenAll(tasks, Function(data)
' Propagate all exceptions and mark all faulted tasks as observed.
Task.WaitAll(data)
' Combine the results from all tasks.
Dim sb As New StringBuilder()
For Each t As Task(Of String) In data
sb.Append(t.Result)
Next
' Final result to be returned eventually on the calling thread.
Return sb.ToString()
End Function)
End Function
'</snippet06>
Class MyCustomState
Public StateData As String
Public Sub New()
StateData = "Hello"
End Sub
End Class
End Class
End ModuleSynchronize multiple FromAsync tasks
The static System.Threading.Tasks.TaskFactory.ContinueWhenAll and System.Threading.Tasks.TaskFactory.ContinueWhenAny methods provide added flexibility when used in conjunction with the FromAsync methods. The following example shows how to initiate multiple asynchronous I/O operations, and then wait for all of them to complete before you execute the continuation.
sample · csharpsamples/snippets/csharp/VS_Snippets_Misc/fromasync/cs/fromasync.cs06
using System;
using System.Collections.Concurrent;
using System.Collections.Generic;
using System.Diagnostics;
using System.IO;
using System.Linq;
using System.Text;
using System.Threading;
using System.Threading.Tasks;
using System.Net;
namespace specialNamespaceForOneMethodSignature
{
using System;
class Task<TResult>
{
public TResult TValue;
}
class Dummy <TResult>
{
// <snippet01>
public Task<TResult> FromAsync<TArg1, TArg2, TArg3>(
Func<TArg1, TArg2, TArg3, AsyncCallback, object, IAsyncResult> beginMethod, //BeginRead
Func<IAsyncResult, TResult> endMethod, //EndRead
TArg1 arg1, // the byte[] buffer
TArg2 arg2, // the offset in arg1 at which to start writing data
TArg3 arg3, // the maximum number of bytes to read
object state // optional state information
)
//</snippet01>
{ return new Task<TResult>(); }
}
}
namespace APM_Task
{
class TestFileStreamNaive
{
//<snippet02>
public string GetFileData(string path)
{
FileInfo fi = new FileInfo(path);
byte[] data = new byte[fi.Length];
FileStream fs;
// a using statement is ok here because we Wait before returning
// and will be done with the filestream.
using (fs = new FileStream(path, FileMode.Open, FileAccess.Read, FileShare.Read, data.Length, true))
{
//Task<int> returns the number of bytes read
Task<int> task = Task<int>.Factory.FromAsync(
fs.BeginRead, fs.EndRead, data, 0, data.Length, null);
task.Wait();
return new UTF8Encoding().GetString(data);
}
}
//</snippet02>
static void Main()
{
TestFileStreamNaive instance = new TestFileStreamNaive();
string s = instance.GetFileData("testfile.txt");
}
}
class AsyncResult : IAsyncResult
{
public AsyncResult() { }
public object AsyncState
{
get { return "Hello from a parallel universe."; }
}
public WaitHandle AsyncWaitHandle
{
get { throw new NotImplementedException(); }
}
public bool CompletedSynchronously
{
get { throw new NotImplementedException(); }
}
public bool IsCompleted
{
get { throw new NotImplementedException(); }
}
static IAsyncResult DoSomethingAsynchronously()
{
return new AsyncResult();
}
//<snippet07>
static Task<String> ReturnTaskFromAsyncResult()
{
IAsyncResult ar = DoSomethingAsynchronously();
Task<String> t = Task<string>.Factory.FromAsync(ar, _ =>
{
return (string)ar.AsyncState;
});
return t;
}
//</snippet07>
}
//<snippet08>
class WebDataDownloader
{
static void Main()
{
WebDataDownloader downloader = new WebDataDownloader();
string[] addresses = { "http://www.msnbc.com", "http://www.yahoo.com",
"http://www.nytimes.com", "http://www.washingtonpost.com",
"http://www.latimes.com", "http://www.newsday.com" };
CancellationTokenSource cts = new CancellationTokenSource();
// Create a UI thread from which to cancel the entire operation
Task.Factory.StartNew(() =>
{
Console.WriteLine("Press c to cancel");
if (Console.ReadKey().KeyChar == 'c')
cts.Cancel();
});
// Using a neutral search term that is sure to get some hits.
Task<string[]> webTask = downloader.GetWordCounts(addresses, "the", cts.Token);
// Do some other work here unless the method has already completed.
if (!webTask.IsCompleted)
{
// Simulate some work.
Thread.SpinWait(5000000);
}
string[] results = null;
try
{
results = webTask.Result;
}
catch (AggregateException e)
{
foreach (var ex in e.InnerExceptions)
{
OperationCanceledException oce = ex as OperationCanceledException;
if (oce != null)
{
if (oce.CancellationToken == cts.Token)
{
Console.WriteLine("Operation canceled by user.");
}
}
else
{
Console.WriteLine(ex.Message);
}
}
}
finally
{
cts.Dispose();
}
if (results != null)
{
foreach (var item in results)
Console.WriteLine(item);
}
Console.ReadKey();
}
Task<string[]> GetWordCounts(string[] urls, string name, CancellationToken token)
{
TaskCompletionSource<string[]> tcs = new TaskCompletionSource<string[]>();
WebClient[] webClients = new WebClient[urls.Length];
// If the user cancels the CancellationToken, then we can use the
// WebClient's ability to cancel its own async operations.
token.Register(() =>
{
foreach (var wc in webClients)
{
if (wc != null)
wc.CancelAsync();
}
});
object m_lock = new object();
int count = 0;
List<string> results = new List<string>();
for (int i = 0; i < urls.Length; i++)
{
webClients[i] = new WebClient();
#region callback
// Specify the callback for the DownloadStringCompleted
// event that will be raised by this WebClient instance.
webClients[i].DownloadStringCompleted += (obj, args) =>
{
if (args.Cancelled == true)
{
tcs.TrySetCanceled();
return;
}
else if (args.Error != null)
{
// Pass through to the underlying Task
// any exceptions thrown by the WebClient
// during the asynchronous operation.
tcs.TrySetException(args.Error);
return;
}
else
{
// Split the string into an array of words,
// then count the number of elements that match
// the search term.
string[] words = null;
words = args.Result.Split(' ');
string NAME = name.ToUpper();
int nameCount = (from word in words.AsParallel()
where word.ToUpper().Contains(NAME)
select word)
.Count();
// Associate the results with the url, and add new string to the array that
// the underlying Task object will return in its Result property.
results.Add(String.Format("{0} has {1} instances of {2}", args.UserState, nameCount, name));
}
// If this is the last async operation to complete,
// then set the Result property on the underlying Task.
lock (m_lock)
{
count++;
if (count == urls.Length)
{
tcs.TrySetResult(results.ToArray());
}
}
};
#endregion
// Call DownloadStringAsync for each URL.
Uri address = null;
try
{
address = new Uri(urls[i]);
// Pass the address, and also use it for the userToken
// to identify the page when the delegate is invoked.
webClients[i].DownloadStringAsync(address, address);
}
catch (UriFormatException ex)
{
// Abandon the entire operation if one url is malformed.
// Other actions are possible here.
tcs.TrySetException(ex);
return tcs.Task;
}
}
// Return the underlying Task. The client code
// waits on the Result property, and handles exceptions
// in the try-catch block there.
return tcs.Task;
}
//</snippet08>
}
#region snippet09
class Calculator
{
public IAsyncResult BeginCalculate(int decimalPlaces, AsyncCallback ac, object state)
{
Console.WriteLine($"Calling BeginCalculate on thread {Thread.CurrentThread.ManagedThreadId}");
Task<string> f = Task<string>.Factory.StartNew(_ => Compute(decimalPlaces), state);
if (ac != null) f.ContinueWith((res) => ac(f));
return f;
}
public string Compute(int numPlaces)
{
Console.WriteLine($"Calling compute on thread {Thread.CurrentThread.ManagedThreadId}");
// Simulating some heavy work.
Thread.SpinWait(500000000);
// Actual implementation left as exercise for the reader.
// Several examples are available on the Web.
return "3.14159265358979323846264338327950288";
}
public string EndCalculate(IAsyncResult ar)
{
Console.WriteLine($"Calling EndCalculate on thread {Thread.CurrentThread.ManagedThreadId}");
return ((Task<string>)ar).Result;
}
}
public class CalculatorClient
{
static int decimalPlaces = 12;
public static void Main()
{
Calculator calc = new Calculator();
int places = 35;
AsyncCallback callBack = new AsyncCallback(PrintResult);
IAsyncResult ar = calc.BeginCalculate(places, callBack, calc);
// Do some work on this thread while the calculator is busy.
Console.WriteLine("Working...");
Thread.SpinWait(500000);
Console.ReadLine();
}
public static void PrintResult(IAsyncResult result)
{
Calculator c = (Calculator)result.AsyncState;
string piString = c.EndCalculate(result);
Console.WriteLine($"Calling PrintResult on thread {Thread.CurrentThread.ManagedThreadId}; result = {piString}");
}
}
#endregion
} //end APM_Task namespace
class FileStreamDemo
{
static void Main()
{
FileStreamDemo fsd = new FileStreamDemo();
// var task = fsd.GetMultiFileData(new string[1]);
fsd.ShowCallingFromAsync();
// fsd.ShowCallingFromAsyncFileData();
// fsd.ProcessFilesAsync();
// task.Wait();
// Console.WriteLine(task.Result);
Console.WriteLine("press any key");
Console.ReadLine();
}
//<snippet03>
const int MAX_FILE_SIZE = 14000000;
public static Task<string> GetFileStringAsync(string path)
{
FileInfo fi = new FileInfo(path);
byte[] data = null;
data = new byte[fi.Length];
FileStream fs = new FileStream(path, FileMode.Open, FileAccess.Read, FileShare.Read, data.Length, true);
//Task<int> returns the number of bytes read
Task<int> task = Task<int>.Factory.FromAsync(
fs.BeginRead, fs.EndRead, data, 0, data.Length, null);
// It is possible to do other work here while waiting
// for the antecedent task to complete.
// ...
// Add the continuation, which returns a Task<string>.
return task.ContinueWith((antecedent) =>
{
fs.Close();
// Result = "number of bytes read" (if we need it.)
if (antecedent.Result < 100)
{
return "Data is too small to bother with.";
}
else
{
// If we did not receive the entire file, the end of the
// data buffer will contain garbage.
if (antecedent.Result < data.Length)
Array.Resize(ref data, antecedent.Result);
// Will be returned in the Result property of the Task<string>
// at some future point after the asynchronous file I/O operation completes.
return new UTF8Encoding().GetString(data);
}
});
}
//</snippet03>
void ShowCallingFromAsync()
{
string path = @"\\docbuild2\public\Main\Logs\DllDiffReport\DllDiffReport_BetweenInBuildAndInProduct.html";
//<snippet04>
Task<string> t = GetFileStringAsync(path);
// Do some other work:
// ...
try
{
Console.WriteLine(t.Result.Substring(0, 500));
}
catch (AggregateException ae)
{
Console.WriteLine(ae.InnerException.Message);
}
//</snippet04>
Console.ReadLine();
}
//not used???
//<snippet12>
public static Task<int> GetFileDataAsync(string path, ref byte[] data)
{
// Error handling omitted for brevity...
FileInfo fi = new FileInfo(path);
data = new byte[fi.Length];
FileStream fs = new FileStream(path, FileMode.Open, FileAccess.Read, FileShare.Read, data.Length, true);
// Task<int> returns the number of bytes read
// Pass FileStream in AsyncState parameter in order to close it from the call site.
return Task<int>.Factory.FromAsync(
fs.BeginRead, fs.EndRead, data, 0, data.Length, fs);
}
//</snippet12>
void ShowCallingFromAsyncFileData()
{
//<snippet13>
string path = @"\\remoteComputer\filename.txt";
byte[] buffer = null;
Task<int> t = GetFileDataAsync(path, ref buffer);
// Can do some other work here:
// ...
for(int i = 0; i < 10; i++)
Console.Write("Working... ");
var result =
t.ContinueWith((antecedent) =>
{
// Error handling omitted...
return new UTF8Encoding().GetString(buffer);
});
// Can also do some other work here:
// ...
for (int i = 0; i < 10; i++)
Console.Write("Working more... ");
try
{
t.Wait();
Console.WriteLine(result.Result.Substring(0, 50));
}
catch (AggregateException ae)
{
Console.WriteLine(ae.InnerException.Message);
}
//</snippet13>
Console.ReadLine();
}
// nested dummy class for snippet0 5 below
class MyCustomState
{
public string StateData { get; set; }
public MyCustomState() { StateData = "Hello"; }
}
private MyCustomState GetCustomState()
{
return new MyCustomState();
}
//<snippet05>
public Task<string> GetFileStringAsync2(string path)
{
FileInfo fi = new FileInfo(path);
byte[] data = new byte[fi.Length];
MyCustomState state = GetCustomState();
FileStream fs = new FileStream(path, FileMode.Open, FileAccess.Read, FileShare.Read, data.Length, true);
// We still pass null for the last parameter because
// the state variable is visible to the continuation delegate.
Task<int> task = Task<int>.Factory.FromAsync(
fs.BeginRead, fs.EndRead, data, 0, data.Length, null);
return task.ContinueWith((antecedent) =>
{
// It is safe to close the filestream now.
fs.Close();
// Capture custom state data directly in the user delegate.
// No need to pass it through the FromAsync method.
if (state.StateData.Contains("New York, New York"))
{
return "Start spreading the news!";
}
else
{
// If we did not receive the entire file, the end of the
// data buffer will contain garbage.
if (antecedent.Result < data.Length)
Array.Resize(ref data, antecedent.Result);
// Will be returned in the Result property of the Task<string>
// at some future point after the asynchronous file I/O operation completes.
return new UTF8Encoding().GetString(data);
}
});
}
//</snippet05>
string[] GetFilesToRead()
{
return new string[3] { "test.txt", "test1.txt", "test2.txt" };
}
//<snippet06>
public Task<string> GetMultiFileData(string[] filesToRead)
{
FileStream fs;
Task<string>[] tasks = new Task<string>[filesToRead.Length];
byte[] fileData = null;
for (int i = 0; i < filesToRead.Length; i++)
{
fileData = new byte[0x1000];
fs = new FileStream(filesToRead[i], FileMode.Open, FileAccess.Read, FileShare.Read, fileData.Length, true);
// By adding the continuation here, the
// Result of each task will be a string.
tasks[i] = Task<int>.Factory.FromAsync(
fs.BeginRead, fs.EndRead, fileData, 0, fileData.Length, null)
.ContinueWith((antecedent) =>
{
fs.Close();
// If we did not receive the entire file, the end of the
// data buffer will contain garbage.
if (antecedent.Result < fileData.Length)
Array.Resize(ref fileData, antecedent.Result);
// Will be returned in the Result property of the Task<string>
// at some future point after the asynchronous file I/O operation completes.
return new UTF8Encoding().GetString(fileData);
});
}
// Wait for all tasks to complete.
return Task<string>.Factory.ContinueWhenAll(tasks, (data) =>
{
// Propagate all exceptions and mark all faulted tasks as observed.
Task.WaitAll(data);
// Combine the results from all tasks.
StringBuilder sb = new StringBuilder();
foreach (var t in data)
{
sb.Append(t.Result);
}
// Final result to be returned eventually on the calling thread.
return sb.ToString();
});
}
//</snippet06>
public string ProcessData(Task[] arr)
{
return "processed";
}
//<snippet11>
void ProcessFilesAsync()
{
string[] files = Directory.GetFiles(@"\\remoteComputer\folderName\", "*.*", SearchOption.AllDirectories);
CancellationTokenSource cts = new CancellationTokenSource();
List<Task<string>> tasks = new List<Task<string>>();
foreach (var file in files)
{
Task<string> t = null;
try
{
t = GetFileStringAsync3(file, cts.Token);
}
catch
{
Console.WriteLine($"Argument exception on {file}");
continue;
}
t.ContinueWith((antecedent) => ProcessFileData(antecedent.Result));
tasks.Add(t);
}
Console.WriteLine("All tasks have been added.");
// Do some work here.
try
{
Task.WaitAll(tasks.ToArray());
Console.WriteLine("All tasks have completed.");
}
catch (AggregateException ae)
{
foreach (var ex in ae.InnerExceptions)
Console.WriteLine(ex.Message);
}
finally
{
cts.Dispose();
}
// If needed, perform a final step after all tasks have completed.
Task.Factory.ContinueWhenAll(tasks.ToArray(), (arr) =>
{
foreach (var t in arr)
{
CompareFileData(t.Result);
}
});
}
public Task<string> GetFileStringAsync3(string path, CancellationToken token)
{
if (!File.Exists(path))
{
throw new FileNotFoundException(String.Format("Could not find {0}", path));
}
FileInfo fi = new FileInfo(path);
byte[] data = null;
if (fi.Length < MAX_FILE_SIZE && fi.Length > 0)
{
data = new byte[fi.Length];
}
else
{
throw new ArgumentException(String.Format("{0} is too big to load!", path));
}
FileStream fs = new FileStream(path, FileMode.Open, FileAccess.Read, FileShare.Read, data.Length, true);
// We still pass null for the last parameter because
// the state variable is visible to the continuation delegate.
Task<int> task = Task<int>.Factory.FromAsync(
fs.BeginRead, fs.EndRead, data, 0, data.Length, null);
return task.ContinueWith((antecedent) =>
{
fs.Close();
// If we did not receive the entire file, the end of the
// data buffer will contain garbage.
if (antecedent.Result < data.Length)
Array.Resize(ref data, antecedent.Result);
// Will be returned in the Result property of the Task<string>
// at some future point after the asynchronous file I/O operation completes.
return new UTF8Encoding().GetString(data);
});
}
string ProcessFileData(string data)
{
string s = data.Substring(0, 80);
Console.WriteLine(s);
return s;
}
string CompareFileData(string s)
{
return "compare results";
}
//</snippet11>
}sample · vbsamples/snippets/visualbasic/VS_Snippets_Misc/fromasync/vb/module1.vb06
Imports System.Collections.Generic
Imports System.IO
Imports System.Net
Imports System.Text
Imports System.Threading
Imports System.Threading.Tasks
Namespace specialNamespaceForOneMethodSignature
Class Task(Of TResult)
Public TValue As TResult
End Class
Class Dummy(Of TResult)
'<snippet01>
Public Function FromAsync(Of TArg1, TArg2, TArg3)(
ByVal beginMethod As Func(Of TArg1, TArg2, TArg3, AsyncCallback, Object, IAsyncResult),
ByVal endMethod As Func(Of IAsyncResult, TResult),
ByVal dataBuffer As TArg1,
ByVal byteOffsetToStartAt As TArg2,
ByVal maxBytesToRead As TArg3,
ByVal stateInfo As Object)
'</snippet01>
Return New Task(Of TResult)
End Function
End Class
End Namespace
Module Module1
Class AsyncResult
Public Sub New()
End Sub
'<snippet07>
Shared Function ReturnTaskFromAsyncResult() As Task(Of String)
Dim ar As IAsyncResult = DoSomethingAsynchronously()
Dim t As Task(Of String) = Task(Of String).Factory.FromAsync(ar, Function(res) CStr(res.AsyncState))
Return t
End Function
'</snippet07>
Private Shared Function DoSomethingAsynchronously() As IAsyncResult
Throw New NotImplementedException
End Function
End Class
'<snippet08>
Class WebDataDownLoader
Dim tcs As New TaskCompletionSource(Of String())
Dim nameToSearch As String
Dim token As CancellationToken
Dim results As New List(Of String)
Dim m_lock As Object
Dim count As Integer
Dim addresses() As String
Shared Sub Main()
Dim downloader As New WebDataDownLoader()
downloader.addresses = {"http://www.msnbc.com", "http://www.yahoo.com", _
"http://www.nytimes.com", "http://www.washingtonpost.com", _
"http://www.latimes.com", "http://www.newsday.com"}
Dim cts As New CancellationTokenSource()
' Create a UI thread from which to cancel the entire operation
Task.Factory.StartNew(Sub()
Console.WriteLine("Press c to cancel")
If Console.ReadKey().KeyChar = "c"c Then
cts.Cancel()
End If
End Sub)
' Using a neutral search term that is sure to get some hits on English web sites.
' Please substitute your favorite search term.
downloader.nameToSearch = "the"
Dim webTask As Task(Of String()) = downloader.GetWordCounts(downloader.addresses, downloader.nameToSearch, cts.Token)
' Do some other work here unless the method has already completed.
If (webTask.IsCompleted = False) Then
' Simulate some work
Thread.SpinWait(5000000)
End If
Dim results As String() = Nothing
Try
results = webTask.Result
Catch ae As AggregateException
For Each ex As Exception In ae.InnerExceptions
If (TypeOf (ex) Is OperationCanceledException) Then
Dim oce As OperationCanceledException = CType(ex, OperationCanceledException)
If oce.CancellationToken = cts.Token Then
Console.WriteLine("Operation canceled by user.")
End If
Else
Console.WriteLine(ex.Message)
End If
Next
Finally
cts.Dispose()
End Try
If (Not results Is Nothing) Then
For Each item As String In results
Console.WriteLine(item)
Next
End If
Console.WriteLine("Press any key to exit")
Console.ReadKey()
End Sub
Public Function GetWordCounts(ByVal urls() As String, ByVal str As String, ByVal token As CancellationToken) As Task(Of String())
Dim webClients() As WebClient
ReDim webClients(urls.Length)
m_lock = New Object()
' If the user cancels the CancellationToken, then we can use the
' WebClient's ability to cancel its own async operations.
token.Register(Sub()
For Each wc As WebClient In webClients
If Not wc Is Nothing Then
wc.CancelAsync()
End If
Next
End Sub)
For i As Integer = 0 To urls.Length - 1
webClients(i) = New WebClient()
' Specify the callback for the DownloadStringCompleted
' event that will be raised by this WebClient instance.
AddHandler webClients(i).DownloadStringCompleted, AddressOf WebEventHandler
Dim address As Uri = Nothing
Try
address = New Uri(urls(i))
' Pass the address, and also use it for the userToken
' to identify the page when the delegate is invoked.
webClients(i).DownloadStringAsync(address, address)
Catch ex As UriFormatException
tcs.TrySetException(ex)
Return tcs.Task
End Try
Next
' Return the underlying Task. The client code
' waits on the Result property, and handles exceptions
' in the try-catch block there.
Return tcs.Task
End Function
Public Sub WebEventHandler(ByVal sender As Object, ByVal args As DownloadStringCompletedEventArgs)
If args.Cancelled = True Then
tcs.TrySetCanceled()
Return
ElseIf Not args.Error Is Nothing Then
tcs.TrySetException(args.Error)
Return
Else
' Split the string into an array of words,
' then count the number of elements that match
' the search term.
Dim words() As String = args.Result.Split(" "c)
Dim NAME As String = nameToSearch.ToUpper()
Dim nameCount = (From word In words.AsParallel()
Where word.ToUpper().Contains(NAME)
Select word).Count()
' Associate the results with the url, and add new string to the array that
' the underlying Task object will return in its Result property.
results.Add(String.Format("{0} has {1} instances of {2}", args.UserState, nameCount, nameToSearch))
End If
SyncLock (m_lock)
count = count + 1
If (count = addresses.Length) Then
tcs.TrySetResult(results.ToArray())
End If
End SyncLock
End Sub
'</snippet08>
End Class
'<snippet09>
Class Calculator
Public Function BeginCalculate(ByVal decimalPlaces As Integer, ByVal ac As AsyncCallback, ByVal state As Object) As IAsyncResult
Console.WriteLine("Calling BeginCalculate on thread {0}", Thread.CurrentThread.ManagedThreadId)
Dim myTask = Task(Of String).Factory.StartNew(Function(obj) Compute(decimalPlaces), state)
myTask.ContinueWith(Sub(antecedent) ac(myTask))
End Function
Private Function Compute(ByVal decimalPlaces As Integer)
Console.WriteLine("Calling compute on thread {0}", Thread.CurrentThread.ManagedThreadId)
' Simulating some heavy work.
Thread.SpinWait(500000000)
' Actual implementation left as exercise for the reader.
' Several examples are available on the Web.
Return "3.14159265358979323846264338327950288"
End Function
Public Function EndCalculate(ByVal ar As IAsyncResult) As String
Console.WriteLine("Calling EndCalculate on thread {0}", Thread.CurrentThread.ManagedThreadId)
Return CType(ar, Task(Of String)).Result
End Function
End Class
Class CalculatorClient
Shared decimalPlaces As Integer
Shared Sub Main()
Dim calc As New Calculator
Dim places As Integer = 35
Dim callback As New AsyncCallback(AddressOf PrintResult)
Dim ar As IAsyncResult = calc.BeginCalculate(places, callback, calc)
' Do some work on this thread while the calculator is busy.
Console.WriteLine("Working...")
Thread.SpinWait(500000)
Console.ReadLine()
End Sub
Public Shared Sub PrintResult(ByVal result As IAsyncResult)
Dim c As Calculator = CType(result.AsyncState, Calculator)
Dim piString As String = c.EndCalculate(result)
Console.WriteLine("Calling PrintResult on thread {0}; result = {1}",
Thread.CurrentThread.ManagedThreadId, piString)
End Sub
End Class
'</snippet09>
Class FileStreamDemo
Shared Sub Main()
Dim fsd As New FileStreamDemo()
fsd.ShowCallingFromAsync()
End Sub
'<snippet03>
Const MAX_FILE_SIZE As Integer = 14000000
Shared Function GetFileStringAsync(ByVal path As String) As Task(Of String)
Dim fi As New FileInfo(path)
Dim data(fi.Length - 1) As Byte
Dim fs As FileStream = New FileStream(path, FileMode.Open, FileAccess.Read, FileShare.Read, data.Length, True)
' Task(Of Integer) returns the number of bytes read
Dim myTask As Task(Of Integer) = Task(Of Integer).Factory.FromAsync(
AddressOf fs.BeginRead, AddressOf fs.EndRead, data, 0, data.Length, Nothing)
' It is possible to do other work here while waiting
' for the antecedent task to complete.
' ...
' Add the continuation, which returns a Task<string>.
Return myTask.ContinueWith(Function(antecedent)
fs.Close()
If (antecedent.Result < 100) Then
Return "Data is too small to bother with."
End If
' If we did not receive the entire file, the end of the
' data buffer will contain garbage.
If (antecedent.Result < data.Length) Then
Array.Resize(data, antecedent.Result)
End If
' Will be returned in the Result property of the Task<string>
' at some future point after the asynchronous file I/O operation completes.
Return New UTF8Encoding().GetString(data)
End Function)
End Function
'</snippet03>
Public Sub ShowCallingFromAsync()
Dim path As String = "\\docbuild2\public\Main\Logs\DllDiffReport\DllDiffReport_BetweenInBuildAndInPublicShare.html"
'<snippet04>
Dim myTask As Task(Of String) = GetFileStringAsync(path)
' Do some other work
' ...
Try
Console.WriteLine(myTask.Result.Substring(0, 500))
Catch ex As AggregateException
Console.WriteLine(ex.InnerException.Message)
End Try
'</snippet04>
Console.WriteLine("Press Enter to exit.")
Console.ReadLine()
End Sub
'<snippet05>
Public Function GetFileStringAsync2(ByVal path As String) As Task(Of String)
Dim fi = New FileInfo(path)
Dim data(fi.Length - 1) As Byte
Dim state As New MyCustomState()
Dim fs As New FileStream(path, FileMode.Open, FileAccess.Read, FileShare.Read, data.Length, True)
' We still pass null for the last parameter because
' the state variable is visible to the continuation delegate.
Dim myTask As Task(Of Integer) = Task(Of Integer).Factory.FromAsync(
AddressOf fs.BeginRead, AddressOf fs.EndRead, data, 0, data.Length, Nothing)
Return myTask.ContinueWith(Function(antecedent)
fs.Close()
' Capture custom state data directly in the user delegate.
' No need to pass it through the FromAsync method.
If (state.StateData.Contains("New York, New York")) Then
Return "Start spreading the news!"
End If
' If we did not receive the entire file, the end of the
' data buffer will contain garbage.
If (antecedent.Result < data.Length) Then
Array.Resize(data, antecedent.Result)
End If
'/ Will be returned in the Result property of the Task<string>
'/ at some future point after the asynchronous file I/O operation completes.
Return New UTF8Encoding().GetString(data)
End Function)
End Function
'</snippet05>
'<snippet06>
Public Function GetMultiFileData(ByVal filesToRead As String()) As Task(Of String)
Dim fs As FileStream
Dim tasks(filesToRead.Length - 1) As Task(Of String)
Dim fileData() As Byte = Nothing
For i As Integer = 0 To filesToRead.Length
fileData(&H1000) = New Byte()
fs = New FileStream(filesToRead(i), FileMode.Open, FileAccess.Read, FileShare.Read, fileData.Length, True)
' By adding the continuation here, the
' Result of each task will be a string.
tasks(i) = Task(Of Integer).Factory.FromAsync(AddressOf fs.BeginRead,
AddressOf fs.EndRead,
fileData,
0,
fileData.Length,
Nothing).
ContinueWith(Function(antecedent)
fs.Close()
'If we did not receive the entire file, the end of the
' data buffer will contain garbage.
If (antecedent.Result < fileData.Length) Then
ReDim Preserve fileData(antecedent.Result)
End If
'Will be returned in the Result property of the Task<string>
' at some future point after the asynchronous file I/O operation completes.
Return New UTF8Encoding().GetString(fileData)
End Function)
Next
Return Task(Of String).Factory.ContinueWhenAll(tasks, Function(data)
' Propagate all exceptions and mark all faulted tasks as observed.
Task.WaitAll(data)
' Combine the results from all tasks.
Dim sb As New StringBuilder()
For Each t As Task(Of String) In data
sb.Append(t.Result)
Next
' Final result to be returned eventually on the calling thread.
Return sb.ToString()
End Function)
End Function
'</snippet06>
Class MyCustomState
Public StateData As String
Public Sub New()
StateData = "Hello"
End Sub
End Class
End Class
End ModuleFromAsync tasks for only the End method
For those few cases in which the Begin method requires more than three input parameters or has ref or out parameters, you can use the FromAsync overloads, for example, System.Threading.Tasks.TaskFactory.FromAsync%28System.IAsyncResult%2CSystem.Func%7BSystem.IAsyncResult%2C%7D%29, that represent only the End method. These methods can also be used in any scenario in which you're passed an System.IAsyncResult and want to encapsulate it in a Task.
sample · csharpsamples/snippets/csharp/VS_Snippets_Misc/fromasync/cs/fromasync.cs07
using System;
using System.Collections.Concurrent;
using System.Collections.Generic;
using System.Diagnostics;
using System.IO;
using System.Linq;
using System.Text;
using System.Threading;
using System.Threading.Tasks;
using System.Net;
namespace specialNamespaceForOneMethodSignature
{
using System;
class Task<TResult>
{
public TResult TValue;
}
class Dummy <TResult>
{
// <snippet01>
public Task<TResult> FromAsync<TArg1, TArg2, TArg3>(
Func<TArg1, TArg2, TArg3, AsyncCallback, object, IAsyncResult> beginMethod, //BeginRead
Func<IAsyncResult, TResult> endMethod, //EndRead
TArg1 arg1, // the byte[] buffer
TArg2 arg2, // the offset in arg1 at which to start writing data
TArg3 arg3, // the maximum number of bytes to read
object state // optional state information
)
//</snippet01>
{ return new Task<TResult>(); }
}
}
namespace APM_Task
{
class TestFileStreamNaive
{
//<snippet02>
public string GetFileData(string path)
{
FileInfo fi = new FileInfo(path);
byte[] data = new byte[fi.Length];
FileStream fs;
// a using statement is ok here because we Wait before returning
// and will be done with the filestream.
using (fs = new FileStream(path, FileMode.Open, FileAccess.Read, FileShare.Read, data.Length, true))
{
//Task<int> returns the number of bytes read
Task<int> task = Task<int>.Factory.FromAsync(
fs.BeginRead, fs.EndRead, data, 0, data.Length, null);
task.Wait();
return new UTF8Encoding().GetString(data);
}
}
//</snippet02>
static void Main()
{
TestFileStreamNaive instance = new TestFileStreamNaive();
string s = instance.GetFileData("testfile.txt");
}
}
class AsyncResult : IAsyncResult
{
public AsyncResult() { }
public object AsyncState
{
get { return "Hello from a parallel universe."; }
}
public WaitHandle AsyncWaitHandle
{
get { throw new NotImplementedException(); }
}
public bool CompletedSynchronously
{
get { throw new NotImplementedException(); }
}
public bool IsCompleted
{
get { throw new NotImplementedException(); }
}
static IAsyncResult DoSomethingAsynchronously()
{
return new AsyncResult();
}
//<snippet07>
static Task<String> ReturnTaskFromAsyncResult()
{
IAsyncResult ar = DoSomethingAsynchronously();
Task<String> t = Task<string>.Factory.FromAsync(ar, _ =>
{
return (string)ar.AsyncState;
});
return t;
}
//</snippet07>
}
//<snippet08>
class WebDataDownloader
{
static void Main()
{
WebDataDownloader downloader = new WebDataDownloader();
string[] addresses = { "http://www.msnbc.com", "http://www.yahoo.com",
"http://www.nytimes.com", "http://www.washingtonpost.com",
"http://www.latimes.com", "http://www.newsday.com" };
CancellationTokenSource cts = new CancellationTokenSource();
// Create a UI thread from which to cancel the entire operation
Task.Factory.StartNew(() =>
{
Console.WriteLine("Press c to cancel");
if (Console.ReadKey().KeyChar == 'c')
cts.Cancel();
});
// Using a neutral search term that is sure to get some hits.
Task<string[]> webTask = downloader.GetWordCounts(addresses, "the", cts.Token);
// Do some other work here unless the method has already completed.
if (!webTask.IsCompleted)
{
// Simulate some work.
Thread.SpinWait(5000000);
}
string[] results = null;
try
{
results = webTask.Result;
}
catch (AggregateException e)
{
foreach (var ex in e.InnerExceptions)
{
OperationCanceledException oce = ex as OperationCanceledException;
if (oce != null)
{
if (oce.CancellationToken == cts.Token)
{
Console.WriteLine("Operation canceled by user.");
}
}
else
{
Console.WriteLine(ex.Message);
}
}
}
finally
{
cts.Dispose();
}
if (results != null)
{
foreach (var item in results)
Console.WriteLine(item);
}
Console.ReadKey();
}
Task<string[]> GetWordCounts(string[] urls, string name, CancellationToken token)
{
TaskCompletionSource<string[]> tcs = new TaskCompletionSource<string[]>();
WebClient[] webClients = new WebClient[urls.Length];
// If the user cancels the CancellationToken, then we can use the
// WebClient's ability to cancel its own async operations.
token.Register(() =>
{
foreach (var wc in webClients)
{
if (wc != null)
wc.CancelAsync();
}
});
object m_lock = new object();
int count = 0;
List<string> results = new List<string>();
for (int i = 0; i < urls.Length; i++)
{
webClients[i] = new WebClient();
#region callback
// Specify the callback for the DownloadStringCompleted
// event that will be raised by this WebClient instance.
webClients[i].DownloadStringCompleted += (obj, args) =>
{
if (args.Cancelled == true)
{
tcs.TrySetCanceled();
return;
}
else if (args.Error != null)
{
// Pass through to the underlying Task
// any exceptions thrown by the WebClient
// during the asynchronous operation.
tcs.TrySetException(args.Error);
return;
}
else
{
// Split the string into an array of words,
// then count the number of elements that match
// the search term.
string[] words = null;
words = args.Result.Split(' ');
string NAME = name.ToUpper();
int nameCount = (from word in words.AsParallel()
where word.ToUpper().Contains(NAME)
select word)
.Count();
// Associate the results with the url, and add new string to the array that
// the underlying Task object will return in its Result property.
results.Add(String.Format("{0} has {1} instances of {2}", args.UserState, nameCount, name));
}
// If this is the last async operation to complete,
// then set the Result property on the underlying Task.
lock (m_lock)
{
count++;
if (count == urls.Length)
{
tcs.TrySetResult(results.ToArray());
}
}
};
#endregion
// Call DownloadStringAsync for each URL.
Uri address = null;
try
{
address = new Uri(urls[i]);
// Pass the address, and also use it for the userToken
// to identify the page when the delegate is invoked.
webClients[i].DownloadStringAsync(address, address);
}
catch (UriFormatException ex)
{
// Abandon the entire operation if one url is malformed.
// Other actions are possible here.
tcs.TrySetException(ex);
return tcs.Task;
}
}
// Return the underlying Task. The client code
// waits on the Result property, and handles exceptions
// in the try-catch block there.
return tcs.Task;
}
//</snippet08>
}
#region snippet09
class Calculator
{
public IAsyncResult BeginCalculate(int decimalPlaces, AsyncCallback ac, object state)
{
Console.WriteLine($"Calling BeginCalculate on thread {Thread.CurrentThread.ManagedThreadId}");
Task<string> f = Task<string>.Factory.StartNew(_ => Compute(decimalPlaces), state);
if (ac != null) f.ContinueWith((res) => ac(f));
return f;
}
public string Compute(int numPlaces)
{
Console.WriteLine($"Calling compute on thread {Thread.CurrentThread.ManagedThreadId}");
// Simulating some heavy work.
Thread.SpinWait(500000000);
// Actual implementation left as exercise for the reader.
// Several examples are available on the Web.
return "3.14159265358979323846264338327950288";
}
public string EndCalculate(IAsyncResult ar)
{
Console.WriteLine($"Calling EndCalculate on thread {Thread.CurrentThread.ManagedThreadId}");
return ((Task<string>)ar).Result;
}
}
public class CalculatorClient
{
static int decimalPlaces = 12;
public static void Main()
{
Calculator calc = new Calculator();
int places = 35;
AsyncCallback callBack = new AsyncCallback(PrintResult);
IAsyncResult ar = calc.BeginCalculate(places, callBack, calc);
// Do some work on this thread while the calculator is busy.
Console.WriteLine("Working...");
Thread.SpinWait(500000);
Console.ReadLine();
}
public static void PrintResult(IAsyncResult result)
{
Calculator c = (Calculator)result.AsyncState;
string piString = c.EndCalculate(result);
Console.WriteLine($"Calling PrintResult on thread {Thread.CurrentThread.ManagedThreadId}; result = {piString}");
}
}
#endregion
} //end APM_Task namespace
class FileStreamDemo
{
static void Main()
{
FileStreamDemo fsd = new FileStreamDemo();
// var task = fsd.GetMultiFileData(new string[1]);
fsd.ShowCallingFromAsync();
// fsd.ShowCallingFromAsyncFileData();
// fsd.ProcessFilesAsync();
// task.Wait();
// Console.WriteLine(task.Result);
Console.WriteLine("press any key");
Console.ReadLine();
}
//<snippet03>
const int MAX_FILE_SIZE = 14000000;
public static Task<string> GetFileStringAsync(string path)
{
FileInfo fi = new FileInfo(path);
byte[] data = null;
data = new byte[fi.Length];
FileStream fs = new FileStream(path, FileMode.Open, FileAccess.Read, FileShare.Read, data.Length, true);
//Task<int> returns the number of bytes read
Task<int> task = Task<int>.Factory.FromAsync(
fs.BeginRead, fs.EndRead, data, 0, data.Length, null);
// It is possible to do other work here while waiting
// for the antecedent task to complete.
// ...
// Add the continuation, which returns a Task<string>.
return task.ContinueWith((antecedent) =>
{
fs.Close();
// Result = "number of bytes read" (if we need it.)
if (antecedent.Result < 100)
{
return "Data is too small to bother with.";
}
else
{
// If we did not receive the entire file, the end of the
// data buffer will contain garbage.
if (antecedent.Result < data.Length)
Array.Resize(ref data, antecedent.Result);
// Will be returned in the Result property of the Task<string>
// at some future point after the asynchronous file I/O operation completes.
return new UTF8Encoding().GetString(data);
}
});
}
//</snippet03>
void ShowCallingFromAsync()
{
string path = @"\\docbuild2\public\Main\Logs\DllDiffReport\DllDiffReport_BetweenInBuildAndInProduct.html";
//<snippet04>
Task<string> t = GetFileStringAsync(path);
// Do some other work:
// ...
try
{
Console.WriteLine(t.Result.Substring(0, 500));
}
catch (AggregateException ae)
{
Console.WriteLine(ae.InnerException.Message);
}
//</snippet04>
Console.ReadLine();
}
//not used???
//<snippet12>
public static Task<int> GetFileDataAsync(string path, ref byte[] data)
{
// Error handling omitted for brevity...
FileInfo fi = new FileInfo(path);
data = new byte[fi.Length];
FileStream fs = new FileStream(path, FileMode.Open, FileAccess.Read, FileShare.Read, data.Length, true);
// Task<int> returns the number of bytes read
// Pass FileStream in AsyncState parameter in order to close it from the call site.
return Task<int>.Factory.FromAsync(
fs.BeginRead, fs.EndRead, data, 0, data.Length, fs);
}
//</snippet12>
void ShowCallingFromAsyncFileData()
{
//<snippet13>
string path = @"\\remoteComputer\filename.txt";
byte[] buffer = null;
Task<int> t = GetFileDataAsync(path, ref buffer);
// Can do some other work here:
// ...
for(int i = 0; i < 10; i++)
Console.Write("Working... ");
var result =
t.ContinueWith((antecedent) =>
{
// Error handling omitted...
return new UTF8Encoding().GetString(buffer);
});
// Can also do some other work here:
// ...
for (int i = 0; i < 10; i++)
Console.Write("Working more... ");
try
{
t.Wait();
Console.WriteLine(result.Result.Substring(0, 50));
}
catch (AggregateException ae)
{
Console.WriteLine(ae.InnerException.Message);
}
//</snippet13>
Console.ReadLine();
}
// nested dummy class for snippet0 5 below
class MyCustomState
{
public string StateData { get; set; }
public MyCustomState() { StateData = "Hello"; }
}
private MyCustomState GetCustomState()
{
return new MyCustomState();
}
//<snippet05>
public Task<string> GetFileStringAsync2(string path)
{
FileInfo fi = new FileInfo(path);
byte[] data = new byte[fi.Length];
MyCustomState state = GetCustomState();
FileStream fs = new FileStream(path, FileMode.Open, FileAccess.Read, FileShare.Read, data.Length, true);
// We still pass null for the last parameter because
// the state variable is visible to the continuation delegate.
Task<int> task = Task<int>.Factory.FromAsync(
fs.BeginRead, fs.EndRead, data, 0, data.Length, null);
return task.ContinueWith((antecedent) =>
{
// It is safe to close the filestream now.
fs.Close();
// Capture custom state data directly in the user delegate.
// No need to pass it through the FromAsync method.
if (state.StateData.Contains("New York, New York"))
{
return "Start spreading the news!";
}
else
{
// If we did not receive the entire file, the end of the
// data buffer will contain garbage.
if (antecedent.Result < data.Length)
Array.Resize(ref data, antecedent.Result);
// Will be returned in the Result property of the Task<string>
// at some future point after the asynchronous file I/O operation completes.
return new UTF8Encoding().GetString(data);
}
});
}
//</snippet05>
string[] GetFilesToRead()
{
return new string[3] { "test.txt", "test1.txt", "test2.txt" };
}
//<snippet06>
public Task<string> GetMultiFileData(string[] filesToRead)
{
FileStream fs;
Task<string>[] tasks = new Task<string>[filesToRead.Length];
byte[] fileData = null;
for (int i = 0; i < filesToRead.Length; i++)
{
fileData = new byte[0x1000];
fs = new FileStream(filesToRead[i], FileMode.Open, FileAccess.Read, FileShare.Read, fileData.Length, true);
// By adding the continuation here, the
// Result of each task will be a string.
tasks[i] = Task<int>.Factory.FromAsync(
fs.BeginRead, fs.EndRead, fileData, 0, fileData.Length, null)
.ContinueWith((antecedent) =>
{
fs.Close();
// If we did not receive the entire file, the end of the
// data buffer will contain garbage.
if (antecedent.Result < fileData.Length)
Array.Resize(ref fileData, antecedent.Result);
// Will be returned in the Result property of the Task<string>
// at some future point after the asynchronous file I/O operation completes.
return new UTF8Encoding().GetString(fileData);
});
}
// Wait for all tasks to complete.
return Task<string>.Factory.ContinueWhenAll(tasks, (data) =>
{
// Propagate all exceptions and mark all faulted tasks as observed.
Task.WaitAll(data);
// Combine the results from all tasks.
StringBuilder sb = new StringBuilder();
foreach (var t in data)
{
sb.Append(t.Result);
}
// Final result to be returned eventually on the calling thread.
return sb.ToString();
});
}
//</snippet06>
public string ProcessData(Task[] arr)
{
return "processed";
}
//<snippet11>
void ProcessFilesAsync()
{
string[] files = Directory.GetFiles(@"\\remoteComputer\folderName\", "*.*", SearchOption.AllDirectories);
CancellationTokenSource cts = new CancellationTokenSource();
List<Task<string>> tasks = new List<Task<string>>();
foreach (var file in files)
{
Task<string> t = null;
try
{
t = GetFileStringAsync3(file, cts.Token);
}
catch
{
Console.WriteLine($"Argument exception on {file}");
continue;
}
t.ContinueWith((antecedent) => ProcessFileData(antecedent.Result));
tasks.Add(t);
}
Console.WriteLine("All tasks have been added.");
// Do some work here.
try
{
Task.WaitAll(tasks.ToArray());
Console.WriteLine("All tasks have completed.");
}
catch (AggregateException ae)
{
foreach (var ex in ae.InnerExceptions)
Console.WriteLine(ex.Message);
}
finally
{
cts.Dispose();
}
// If needed, perform a final step after all tasks have completed.
Task.Factory.ContinueWhenAll(tasks.ToArray(), (arr) =>
{
foreach (var t in arr)
{
CompareFileData(t.Result);
}
});
}
public Task<string> GetFileStringAsync3(string path, CancellationToken token)
{
if (!File.Exists(path))
{
throw new FileNotFoundException(String.Format("Could not find {0}", path));
}
FileInfo fi = new FileInfo(path);
byte[] data = null;
if (fi.Length < MAX_FILE_SIZE && fi.Length > 0)
{
data = new byte[fi.Length];
}
else
{
throw new ArgumentException(String.Format("{0} is too big to load!", path));
}
FileStream fs = new FileStream(path, FileMode.Open, FileAccess.Read, FileShare.Read, data.Length, true);
// We still pass null for the last parameter because
// the state variable is visible to the continuation delegate.
Task<int> task = Task<int>.Factory.FromAsync(
fs.BeginRead, fs.EndRead, data, 0, data.Length, null);
return task.ContinueWith((antecedent) =>
{
fs.Close();
// If we did not receive the entire file, the end of the
// data buffer will contain garbage.
if (antecedent.Result < data.Length)
Array.Resize(ref data, antecedent.Result);
// Will be returned in the Result property of the Task<string>
// at some future point after the asynchronous file I/O operation completes.
return new UTF8Encoding().GetString(data);
});
}
string ProcessFileData(string data)
{
string s = data.Substring(0, 80);
Console.WriteLine(s);
return s;
}
string CompareFileData(string s)
{
return "compare results";
}
//</snippet11>
}sample · vbsamples/snippets/visualbasic/VS_Snippets_Misc/fromasync/vb/module1.vb07
Imports System.Collections.Generic
Imports System.IO
Imports System.Net
Imports System.Text
Imports System.Threading
Imports System.Threading.Tasks
Namespace specialNamespaceForOneMethodSignature
Class Task(Of TResult)
Public TValue As TResult
End Class
Class Dummy(Of TResult)
'<snippet01>
Public Function FromAsync(Of TArg1, TArg2, TArg3)(
ByVal beginMethod As Func(Of TArg1, TArg2, TArg3, AsyncCallback, Object, IAsyncResult),
ByVal endMethod As Func(Of IAsyncResult, TResult),
ByVal dataBuffer As TArg1,
ByVal byteOffsetToStartAt As TArg2,
ByVal maxBytesToRead As TArg3,
ByVal stateInfo As Object)
'</snippet01>
Return New Task(Of TResult)
End Function
End Class
End Namespace
Module Module1
Class AsyncResult
Public Sub New()
End Sub
'<snippet07>
Shared Function ReturnTaskFromAsyncResult() As Task(Of String)
Dim ar As IAsyncResult = DoSomethingAsynchronously()
Dim t As Task(Of String) = Task(Of String).Factory.FromAsync(ar, Function(res) CStr(res.AsyncState))
Return t
End Function
'</snippet07>
Private Shared Function DoSomethingAsynchronously() As IAsyncResult
Throw New NotImplementedException
End Function
End Class
'<snippet08>
Class WebDataDownLoader
Dim tcs As New TaskCompletionSource(Of String())
Dim nameToSearch As String
Dim token As CancellationToken
Dim results As New List(Of String)
Dim m_lock As Object
Dim count As Integer
Dim addresses() As String
Shared Sub Main()
Dim downloader As New WebDataDownLoader()
downloader.addresses = {"http://www.msnbc.com", "http://www.yahoo.com", _
"http://www.nytimes.com", "http://www.washingtonpost.com", _
"http://www.latimes.com", "http://www.newsday.com"}
Dim cts As New CancellationTokenSource()
' Create a UI thread from which to cancel the entire operation
Task.Factory.StartNew(Sub()
Console.WriteLine("Press c to cancel")
If Console.ReadKey().KeyChar = "c"c Then
cts.Cancel()
End If
End Sub)
' Using a neutral search term that is sure to get some hits on English web sites.
' Please substitute your favorite search term.
downloader.nameToSearch = "the"
Dim webTask As Task(Of String()) = downloader.GetWordCounts(downloader.addresses, downloader.nameToSearch, cts.Token)
' Do some other work here unless the method has already completed.
If (webTask.IsCompleted = False) Then
' Simulate some work
Thread.SpinWait(5000000)
End If
Dim results As String() = Nothing
Try
results = webTask.Result
Catch ae As AggregateException
For Each ex As Exception In ae.InnerExceptions
If (TypeOf (ex) Is OperationCanceledException) Then
Dim oce As OperationCanceledException = CType(ex, OperationCanceledException)
If oce.CancellationToken = cts.Token Then
Console.WriteLine("Operation canceled by user.")
End If
Else
Console.WriteLine(ex.Message)
End If
Next
Finally
cts.Dispose()
End Try
If (Not results Is Nothing) Then
For Each item As String In results
Console.WriteLine(item)
Next
End If
Console.WriteLine("Press any key to exit")
Console.ReadKey()
End Sub
Public Function GetWordCounts(ByVal urls() As String, ByVal str As String, ByVal token As CancellationToken) As Task(Of String())
Dim webClients() As WebClient
ReDim webClients(urls.Length)
m_lock = New Object()
' If the user cancels the CancellationToken, then we can use the
' WebClient's ability to cancel its own async operations.
token.Register(Sub()
For Each wc As WebClient In webClients
If Not wc Is Nothing Then
wc.CancelAsync()
End If
Next
End Sub)
For i As Integer = 0 To urls.Length - 1
webClients(i) = New WebClient()
' Specify the callback for the DownloadStringCompleted
' event that will be raised by this WebClient instance.
AddHandler webClients(i).DownloadStringCompleted, AddressOf WebEventHandler
Dim address As Uri = Nothing
Try
address = New Uri(urls(i))
' Pass the address, and also use it for the userToken
' to identify the page when the delegate is invoked.
webClients(i).DownloadStringAsync(address, address)
Catch ex As UriFormatException
tcs.TrySetException(ex)
Return tcs.Task
End Try
Next
' Return the underlying Task. The client code
' waits on the Result property, and handles exceptions
' in the try-catch block there.
Return tcs.Task
End Function
Public Sub WebEventHandler(ByVal sender As Object, ByVal args As DownloadStringCompletedEventArgs)
If args.Cancelled = True Then
tcs.TrySetCanceled()
Return
ElseIf Not args.Error Is Nothing Then
tcs.TrySetException(args.Error)
Return
Else
' Split the string into an array of words,
' then count the number of elements that match
' the search term.
Dim words() As String = args.Result.Split(" "c)
Dim NAME As String = nameToSearch.ToUpper()
Dim nameCount = (From word In words.AsParallel()
Where word.ToUpper().Contains(NAME)
Select word).Count()
' Associate the results with the url, and add new string to the array that
' the underlying Task object will return in its Result property.
results.Add(String.Format("{0} has {1} instances of {2}", args.UserState, nameCount, nameToSearch))
End If
SyncLock (m_lock)
count = count + 1
If (count = addresses.Length) Then
tcs.TrySetResult(results.ToArray())
End If
End SyncLock
End Sub
'</snippet08>
End Class
'<snippet09>
Class Calculator
Public Function BeginCalculate(ByVal decimalPlaces As Integer, ByVal ac As AsyncCallback, ByVal state As Object) As IAsyncResult
Console.WriteLine("Calling BeginCalculate on thread {0}", Thread.CurrentThread.ManagedThreadId)
Dim myTask = Task(Of String).Factory.StartNew(Function(obj) Compute(decimalPlaces), state)
myTask.ContinueWith(Sub(antecedent) ac(myTask))
End Function
Private Function Compute(ByVal decimalPlaces As Integer)
Console.WriteLine("Calling compute on thread {0}", Thread.CurrentThread.ManagedThreadId)
' Simulating some heavy work.
Thread.SpinWait(500000000)
' Actual implementation left as exercise for the reader.
' Several examples are available on the Web.
Return "3.14159265358979323846264338327950288"
End Function
Public Function EndCalculate(ByVal ar As IAsyncResult) As String
Console.WriteLine("Calling EndCalculate on thread {0}", Thread.CurrentThread.ManagedThreadId)
Return CType(ar, Task(Of String)).Result
End Function
End Class
Class CalculatorClient
Shared decimalPlaces As Integer
Shared Sub Main()
Dim calc As New Calculator
Dim places As Integer = 35
Dim callback As New AsyncCallback(AddressOf PrintResult)
Dim ar As IAsyncResult = calc.BeginCalculate(places, callback, calc)
' Do some work on this thread while the calculator is busy.
Console.WriteLine("Working...")
Thread.SpinWait(500000)
Console.ReadLine()
End Sub
Public Shared Sub PrintResult(ByVal result As IAsyncResult)
Dim c As Calculator = CType(result.AsyncState, Calculator)
Dim piString As String = c.EndCalculate(result)
Console.WriteLine("Calling PrintResult on thread {0}; result = {1}",
Thread.CurrentThread.ManagedThreadId, piString)
End Sub
End Class
'</snippet09>
Class FileStreamDemo
Shared Sub Main()
Dim fsd As New FileStreamDemo()
fsd.ShowCallingFromAsync()
End Sub
'<snippet03>
Const MAX_FILE_SIZE As Integer = 14000000
Shared Function GetFileStringAsync(ByVal path As String) As Task(Of String)
Dim fi As New FileInfo(path)
Dim data(fi.Length - 1) As Byte
Dim fs As FileStream = New FileStream(path, FileMode.Open, FileAccess.Read, FileShare.Read, data.Length, True)
' Task(Of Integer) returns the number of bytes read
Dim myTask As Task(Of Integer) = Task(Of Integer).Factory.FromAsync(
AddressOf fs.BeginRead, AddressOf fs.EndRead, data, 0, data.Length, Nothing)
' It is possible to do other work here while waiting
' for the antecedent task to complete.
' ...
' Add the continuation, which returns a Task<string>.
Return myTask.ContinueWith(Function(antecedent)
fs.Close()
If (antecedent.Result < 100) Then
Return "Data is too small to bother with."
End If
' If we did not receive the entire file, the end of the
' data buffer will contain garbage.
If (antecedent.Result < data.Length) Then
Array.Resize(data, antecedent.Result)
End If
' Will be returned in the Result property of the Task<string>
' at some future point after the asynchronous file I/O operation completes.
Return New UTF8Encoding().GetString(data)
End Function)
End Function
'</snippet03>
Public Sub ShowCallingFromAsync()
Dim path As String = "\\docbuild2\public\Main\Logs\DllDiffReport\DllDiffReport_BetweenInBuildAndInPublicShare.html"
'<snippet04>
Dim myTask As Task(Of String) = GetFileStringAsync(path)
' Do some other work
' ...
Try
Console.WriteLine(myTask.Result.Substring(0, 500))
Catch ex As AggregateException
Console.WriteLine(ex.InnerException.Message)
End Try
'</snippet04>
Console.WriteLine("Press Enter to exit.")
Console.ReadLine()
End Sub
'<snippet05>
Public Function GetFileStringAsync2(ByVal path As String) As Task(Of String)
Dim fi = New FileInfo(path)
Dim data(fi.Length - 1) As Byte
Dim state As New MyCustomState()
Dim fs As New FileStream(path, FileMode.Open, FileAccess.Read, FileShare.Read, data.Length, True)
' We still pass null for the last parameter because
' the state variable is visible to the continuation delegate.
Dim myTask As Task(Of Integer) = Task(Of Integer).Factory.FromAsync(
AddressOf fs.BeginRead, AddressOf fs.EndRead, data, 0, data.Length, Nothing)
Return myTask.ContinueWith(Function(antecedent)
fs.Close()
' Capture custom state data directly in the user delegate.
' No need to pass it through the FromAsync method.
If (state.StateData.Contains("New York, New York")) Then
Return "Start spreading the news!"
End If
' If we did not receive the entire file, the end of the
' data buffer will contain garbage.
If (antecedent.Result < data.Length) Then
Array.Resize(data, antecedent.Result)
End If
'/ Will be returned in the Result property of the Task<string>
'/ at some future point after the asynchronous file I/O operation completes.
Return New UTF8Encoding().GetString(data)
End Function)
End Function
'</snippet05>
'<snippet06>
Public Function GetMultiFileData(ByVal filesToRead As String()) As Task(Of String)
Dim fs As FileStream
Dim tasks(filesToRead.Length - 1) As Task(Of String)
Dim fileData() As Byte = Nothing
For i As Integer = 0 To filesToRead.Length
fileData(&H1000) = New Byte()
fs = New FileStream(filesToRead(i), FileMode.Open, FileAccess.Read, FileShare.Read, fileData.Length, True)
' By adding the continuation here, the
' Result of each task will be a string.
tasks(i) = Task(Of Integer).Factory.FromAsync(AddressOf fs.BeginRead,
AddressOf fs.EndRead,
fileData,
0,
fileData.Length,
Nothing).
ContinueWith(Function(antecedent)
fs.Close()
'If we did not receive the entire file, the end of the
' data buffer will contain garbage.
If (antecedent.Result < fileData.Length) Then
ReDim Preserve fileData(antecedent.Result)
End If
'Will be returned in the Result property of the Task<string>
' at some future point after the asynchronous file I/O operation completes.
Return New UTF8Encoding().GetString(fileData)
End Function)
Next
Return Task(Of String).Factory.ContinueWhenAll(tasks, Function(data)
' Propagate all exceptions and mark all faulted tasks as observed.
Task.WaitAll(data)
' Combine the results from all tasks.
Dim sb As New StringBuilder()
For Each t As Task(Of String) In data
sb.Append(t.Result)
Next
' Final result to be returned eventually on the calling thread.
Return sb.ToString()
End Function)
End Function
'</snippet06>
Class MyCustomState
Public StateData As String
Public Sub New()
StateData = "Hello"
End Sub
End Class
End Class
End ModuleStart and cancel FromAsync tasks
The task returned by a FromAsync method has a status of WaitingForActivation and will be started by the system at some point after the task is created. If you attempt to call Start on such a task, an exception will be raised.
You cannot cancel a FromAsync task, because the underlying .NET APIs currently do not support in-progress cancellation of file or network I/O. You can add cancellation functionality to a method that encapsulates a FromAsync call, but you can only respond to the cancellation before FromAsync is called or after it completed (for example, in a continuation task).
Some classes that support EAP, for example, System.Net.WebClient, do support cancellation, and you can integrate that native cancellation functionality by using cancellation tokens.
Expose complex EAP operations As tasks
The TPL does not provide any methods that are specifically designed to encapsulate an event-based asynchronous operation in the same way that the FromAsync family of methods wrap the System.IAsyncResult pattern. However, the TPL does provide the System.Threading.Tasks.TaskCompletionSource class, which can be used to represent any arbitrary set of operations as a System.Threading.Tasks.Task. The operations may be synchronous or asynchronous, and may be I/O bound or compute-bound, or both.
The following example shows how to use a System.Threading.Tasks.TaskCompletionSource to expose a set of asynchronous System.Net.WebClient operations to client code as a basic System.Threading.Tasks.Task. The method lets you enter an array of Web URLs, and a term or name to search for, and then returns the number of times the search term occurs on each site.
sample · csharpsamples/snippets/csharp/VS_Snippets_Misc/fromasync/cs/snippet10.cs10
// <Snippet10>
using System;
using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Threading;
using System.Threading.Tasks;
public class SimpleWebExample
{
public Task<string[]> GetWordCountsSimplified(string[] urls, string name,
CancellationToken token)
{
TaskCompletionSource<string[]> tcs = new TaskCompletionSource<string[]>();
WebClient[] webClients = new WebClient[urls.Length];
object m_lock = new object();
int count = 0;
List<string> results = new List<string>();
// If the user cancels the CancellationToken, then we can use the
// WebClient's ability to cancel its own async operations.
token.Register(() =>
{
foreach (var wc in webClients)
{
if (wc != null)
wc.CancelAsync();
}
});
for (int i = 0; i < urls.Length; i++)
{
webClients[i] = new WebClient();
#region callback
// Specify the callback for the DownloadStringCompleted
// event that will be raised by this WebClient instance.
webClients[i].DownloadStringCompleted += (obj, args) =>
{
// Argument validation and exception handling omitted for brevity.
// Split the string into an array of words,
// then count the number of elements that match
// the search term.
string[] words = args.Result.Split(' ');
string NAME = name.ToUpper();
int nameCount = (from word in words.AsParallel()
where word.ToUpper().Contains(NAME)
select word)
.Count();
// Associate the results with the url, and add new string to the array that
// the underlying Task object will return in its Result property.
lock (m_lock)
{
results.Add(String.Format("{0} has {1} instances of {2}", args.UserState, nameCount, name));
// If this is the last async operation to complete,
// then set the Result property on the underlying Task.
count++;
if (count == urls.Length)
{
tcs.TrySetResult(results.ToArray());
}
}
};
#endregion
// Call DownloadStringAsync for each URL.
Uri address = null;
address = new Uri(urls[i]);
webClients[i].DownloadStringAsync(address, address);
} // end for
// Return the underlying Task. The client code
// waits on the Result property, and handles exceptions
// in the try-catch block there.
return tcs.Task;
}
}
// </Snippet10>
public class Example
{
public static void Main()
{
string[] urls = {"http://www.microsoft.com",
"http://www.google.com",
"http://www.amazon.com",
"http://www.adobe.com" };
string searchTerm = "investor";
var ex = new SimpleWebExample();
var t = ex.GetWordCountsSimplified(urls, searchTerm, CancellationToken.None);
t.Wait();
foreach (var value in t.Result)
Console.WriteLine(value);
Console.ReadLine();
}
}sample · vbsamples/snippets/visualbasic/VS_Snippets_Misc/fromasync/vb/snippet10.vb10
' Visual Basic .NET Document
Option Strict On
' <Snippet10>
Imports System.Collections.Generic
Imports System.Net
Imports System.Threading
Imports System.Threading.Tasks
Public Class SimpleWebExample
Dim tcs As New TaskCompletionSource(Of String())
Dim token As CancellationToken
Dim results As New List(Of String)
Dim m_lock As New Object()
Dim count As Integer
Dim addresses() As String
Dim nameToSearch As String
Public Function GetWordCountsSimplified(ByVal urls() As String, ByVal str As String,
ByVal token As CancellationToken) As Task(Of String())
addresses = urls
nameToSearch = str
Dim webClients(urls.Length - 1) As WebClient
' If the user cancels the CancellationToken, then we can use the
' WebClient's ability to cancel its own async operations.
token.Register(Sub()
For Each wc As WebClient In webClients
If wc IsNot Nothing Then
wc.CancelAsync()
End If
Next
End Sub)
For i As Integer = 0 To urls.Length - 1
webClients(i) = New WebClient()
' Specify the callback for the DownloadStringCompleted
' event that will be raised by this WebClient instance.
AddHandler webClients(i).DownloadStringCompleted, AddressOf WebEventHandler
Dim address As New Uri(urls(i))
' Pass the address, and also use it for the userToken
' to identify the page when the delegate is invoked.
webClients(i).DownloadStringAsync(address, address)
Next
' Return the underlying Task. The client code
' waits on the Result property, and handles exceptions
' in the try-catch block there.
Return tcs.Task
End Function
Public Sub WebEventHandler(ByVal sender As Object, ByVal args As DownloadStringCompletedEventArgs)
If args.Cancelled = True Then
tcs.TrySetCanceled()
Return
ElseIf args.Error IsNot Nothing Then
tcs.TrySetException(args.Error)
Return
Else
' Split the string into an array of words,
' then count the number of elements that match
' the search term.
Dim words() As String = args.Result.Split(" "c)
Dim name As String = nameToSearch.ToUpper()
Dim nameCount = (From word In words.AsParallel()
Where word.ToUpper().Contains(name)
Select word).Count()
' Associate the results with the url, and add new string to the array that
' the underlying Task object will return in its Result property.
SyncLock (m_lock)
results.Add(String.Format("{0} has {1} instances of {2}", args.UserState, nameCount, nameToSearch))
count = count + 1
If (count = addresses.Length) Then
tcs.TrySetResult(results.ToArray())
End If
End SyncLock
End If
End Sub
End Class
' </snippet10>
Public Module Example
Public Sub Main
Dim urls() As String = {"http:\\www.microsoft.com",
"http:\\www.google.com",
"http:\\www.amazon.com",
"http:\\www.adobe.com"}
Dim searchTerm As String = "investor"
Dim ex As New SimpleWebExample()
Dim t = ex.GetWordCountsSimplified(urls, searchTerm, Nothing)
t.Wait()
For Each value In t.Result
Console.WriteLine(value)
Next
Console.ReadLine()
End Sub
End ModuleFor a more complete example, which includes additional exception handling and shows how to call the method from client code, see How to: Wrap EAP Patterns in a Task.
Remember that any task that's created by a System.Threading.Tasks.TaskCompletionSource will be started by that TaskCompletionSource and, therefore, user code should not call the Start method on that task.
Implement the APM pattern by using tasks
In some scenarios, it may be desirable to directly expose the System.IAsyncResult pattern by using begin/end method pairs in an API. For example, you may want to maintain consistency with existing APIs, or you may have automated tools that require this pattern. In such cases, you can use Task objects to simplify how the APM pattern is implemented internally.
The following example shows how to use tasks to implement an APM begin/end method pair for a long-running compute-bound method.
sample · csharpsamples/snippets/csharp/VS_Snippets_Misc/fromasync/cs/fromasync.cs09
using System;
using System.Collections.Concurrent;
using System.Collections.Generic;
using System.Diagnostics;
using System.IO;
using System.Linq;
using System.Text;
using System.Threading;
using System.Threading.Tasks;
using System.Net;
namespace specialNamespaceForOneMethodSignature
{
using System;
class Task<TResult>
{
public TResult TValue;
}
class Dummy <TResult>
{
// <snippet01>
public Task<TResult> FromAsync<TArg1, TArg2, TArg3>(
Func<TArg1, TArg2, TArg3, AsyncCallback, object, IAsyncResult> beginMethod, //BeginRead
Func<IAsyncResult, TResult> endMethod, //EndRead
TArg1 arg1, // the byte[] buffer
TArg2 arg2, // the offset in arg1 at which to start writing data
TArg3 arg3, // the maximum number of bytes to read
object state // optional state information
)
//</snippet01>
{ return new Task<TResult>(); }
}
}
namespace APM_Task
{
class TestFileStreamNaive
{
//<snippet02>
public string GetFileData(string path)
{
FileInfo fi = new FileInfo(path);
byte[] data = new byte[fi.Length];
FileStream fs;
// a using statement is ok here because we Wait before returning
// and will be done with the filestream.
using (fs = new FileStream(path, FileMode.Open, FileAccess.Read, FileShare.Read, data.Length, true))
{
//Task<int> returns the number of bytes read
Task<int> task = Task<int>.Factory.FromAsync(
fs.BeginRead, fs.EndRead, data, 0, data.Length, null);
task.Wait();
return new UTF8Encoding().GetString(data);
}
}
//</snippet02>
static void Main()
{
TestFileStreamNaive instance = new TestFileStreamNaive();
string s = instance.GetFileData("testfile.txt");
}
}
class AsyncResult : IAsyncResult
{
public AsyncResult() { }
public object AsyncState
{
get { return "Hello from a parallel universe."; }
}
public WaitHandle AsyncWaitHandle
{
get { throw new NotImplementedException(); }
}
public bool CompletedSynchronously
{
get { throw new NotImplementedException(); }
}
public bool IsCompleted
{
get { throw new NotImplementedException(); }
}
static IAsyncResult DoSomethingAsynchronously()
{
return new AsyncResult();
}
//<snippet07>
static Task<String> ReturnTaskFromAsyncResult()
{
IAsyncResult ar = DoSomethingAsynchronously();
Task<String> t = Task<string>.Factory.FromAsync(ar, _ =>
{
return (string)ar.AsyncState;
});
return t;
}
//</snippet07>
}
//<snippet08>
class WebDataDownloader
{
static void Main()
{
WebDataDownloader downloader = new WebDataDownloader();
string[] addresses = { "http://www.msnbc.com", "http://www.yahoo.com",
"http://www.nytimes.com", "http://www.washingtonpost.com",
"http://www.latimes.com", "http://www.newsday.com" };
CancellationTokenSource cts = new CancellationTokenSource();
// Create a UI thread from which to cancel the entire operation
Task.Factory.StartNew(() =>
{
Console.WriteLine("Press c to cancel");
if (Console.ReadKey().KeyChar == 'c')
cts.Cancel();
});
// Using a neutral search term that is sure to get some hits.
Task<string[]> webTask = downloader.GetWordCounts(addresses, "the", cts.Token);
// Do some other work here unless the method has already completed.
if (!webTask.IsCompleted)
{
// Simulate some work.
Thread.SpinWait(5000000);
}
string[] results = null;
try
{
results = webTask.Result;
}
catch (AggregateException e)
{
foreach (var ex in e.InnerExceptions)
{
OperationCanceledException oce = ex as OperationCanceledException;
if (oce != null)
{
if (oce.CancellationToken == cts.Token)
{
Console.WriteLine("Operation canceled by user.");
}
}
else
{
Console.WriteLine(ex.Message);
}
}
}
finally
{
cts.Dispose();
}
if (results != null)
{
foreach (var item in results)
Console.WriteLine(item);
}
Console.ReadKey();
}
Task<string[]> GetWordCounts(string[] urls, string name, CancellationToken token)
{
TaskCompletionSource<string[]> tcs = new TaskCompletionSource<string[]>();
WebClient[] webClients = new WebClient[urls.Length];
// If the user cancels the CancellationToken, then we can use the
// WebClient's ability to cancel its own async operations.
token.Register(() =>
{
foreach (var wc in webClients)
{
if (wc != null)
wc.CancelAsync();
}
});
object m_lock = new object();
int count = 0;
List<string> results = new List<string>();
for (int i = 0; i < urls.Length; i++)
{
webClients[i] = new WebClient();
#region callback
// Specify the callback for the DownloadStringCompleted
// event that will be raised by this WebClient instance.
webClients[i].DownloadStringCompleted += (obj, args) =>
{
if (args.Cancelled == true)
{
tcs.TrySetCanceled();
return;
}
else if (args.Error != null)
{
// Pass through to the underlying Task
// any exceptions thrown by the WebClient
// during the asynchronous operation.
tcs.TrySetException(args.Error);
return;
}
else
{
// Split the string into an array of words,
// then count the number of elements that match
// the search term.
string[] words = null;
words = args.Result.Split(' ');
string NAME = name.ToUpper();
int nameCount = (from word in words.AsParallel()
where word.ToUpper().Contains(NAME)
select word)
.Count();
// Associate the results with the url, and add new string to the array that
// the underlying Task object will return in its Result property.
results.Add(String.Format("{0} has {1} instances of {2}", args.UserState, nameCount, name));
}
// If this is the last async operation to complete,
// then set the Result property on the underlying Task.
lock (m_lock)
{
count++;
if (count == urls.Length)
{
tcs.TrySetResult(results.ToArray());
}
}
};
#endregion
// Call DownloadStringAsync for each URL.
Uri address = null;
try
{
address = new Uri(urls[i]);
// Pass the address, and also use it for the userToken
// to identify the page when the delegate is invoked.
webClients[i].DownloadStringAsync(address, address);
}
catch (UriFormatException ex)
{
// Abandon the entire operation if one url is malformed.
// Other actions are possible here.
tcs.TrySetException(ex);
return tcs.Task;
}
}
// Return the underlying Task. The client code
// waits on the Result property, and handles exceptions
// in the try-catch block there.
return tcs.Task;
}
//</snippet08>
}
#region snippet09
class Calculator
{
public IAsyncResult BeginCalculate(int decimalPlaces, AsyncCallback ac, object state)
{
Console.WriteLine($"Calling BeginCalculate on thread {Thread.CurrentThread.ManagedThreadId}");
Task<string> f = Task<string>.Factory.StartNew(_ => Compute(decimalPlaces), state);
if (ac != null) f.ContinueWith((res) => ac(f));
return f;
}
public string Compute(int numPlaces)
{
Console.WriteLine($"Calling compute on thread {Thread.CurrentThread.ManagedThreadId}");
// Simulating some heavy work.
Thread.SpinWait(500000000);
// Actual implementation left as exercise for the reader.
// Several examples are available on the Web.
return "3.14159265358979323846264338327950288";
}
public string EndCalculate(IAsyncResult ar)
{
Console.WriteLine($"Calling EndCalculate on thread {Thread.CurrentThread.ManagedThreadId}");
return ((Task<string>)ar).Result;
}
}
public class CalculatorClient
{
static int decimalPlaces = 12;
public static void Main()
{
Calculator calc = new Calculator();
int places = 35;
AsyncCallback callBack = new AsyncCallback(PrintResult);
IAsyncResult ar = calc.BeginCalculate(places, callBack, calc);
// Do some work on this thread while the calculator is busy.
Console.WriteLine("Working...");
Thread.SpinWait(500000);
Console.ReadLine();
}
public static void PrintResult(IAsyncResult result)
{
Calculator c = (Calculator)result.AsyncState;
string piString = c.EndCalculate(result);
Console.WriteLine($"Calling PrintResult on thread {Thread.CurrentThread.ManagedThreadId}; result = {piString}");
}
}
#endregion
} //end APM_Task namespace
class FileStreamDemo
{
static void Main()
{
FileStreamDemo fsd = new FileStreamDemo();
// var task = fsd.GetMultiFileData(new string[1]);
fsd.ShowCallingFromAsync();
// fsd.ShowCallingFromAsyncFileData();
// fsd.ProcessFilesAsync();
// task.Wait();
// Console.WriteLine(task.Result);
Console.WriteLine("press any key");
Console.ReadLine();
}
//<snippet03>
const int MAX_FILE_SIZE = 14000000;
public static Task<string> GetFileStringAsync(string path)
{
FileInfo fi = new FileInfo(path);
byte[] data = null;
data = new byte[fi.Length];
FileStream fs = new FileStream(path, FileMode.Open, FileAccess.Read, FileShare.Read, data.Length, true);
//Task<int> returns the number of bytes read
Task<int> task = Task<int>.Factory.FromAsync(
fs.BeginRead, fs.EndRead, data, 0, data.Length, null);
// It is possible to do other work here while waiting
// for the antecedent task to complete.
// ...
// Add the continuation, which returns a Task<string>.
return task.ContinueWith((antecedent) =>
{
fs.Close();
// Result = "number of bytes read" (if we need it.)
if (antecedent.Result < 100)
{
return "Data is too small to bother with.";
}
else
{
// If we did not receive the entire file, the end of the
// data buffer will contain garbage.
if (antecedent.Result < data.Length)
Array.Resize(ref data, antecedent.Result);
// Will be returned in the Result property of the Task<string>
// at some future point after the asynchronous file I/O operation completes.
return new UTF8Encoding().GetString(data);
}
});
}
//</snippet03>
void ShowCallingFromAsync()
{
string path = @"\\docbuild2\public\Main\Logs\DllDiffReport\DllDiffReport_BetweenInBuildAndInProduct.html";
//<snippet04>
Task<string> t = GetFileStringAsync(path);
// Do some other work:
// ...
try
{
Console.WriteLine(t.Result.Substring(0, 500));
}
catch (AggregateException ae)
{
Console.WriteLine(ae.InnerException.Message);
}
//</snippet04>
Console.ReadLine();
}
//not used???
//<snippet12>
public static Task<int> GetFileDataAsync(string path, ref byte[] data)
{
// Error handling omitted for brevity...
FileInfo fi = new FileInfo(path);
data = new byte[fi.Length];
FileStream fs = new FileStream(path, FileMode.Open, FileAccess.Read, FileShare.Read, data.Length, true);
// Task<int> returns the number of bytes read
// Pass FileStream in AsyncState parameter in order to close it from the call site.
return Task<int>.Factory.FromAsync(
fs.BeginRead, fs.EndRead, data, 0, data.Length, fs);
}
//</snippet12>
void ShowCallingFromAsyncFileData()
{
//<snippet13>
string path = @"\\remoteComputer\filename.txt";
byte[] buffer = null;
Task<int> t = GetFileDataAsync(path, ref buffer);
// Can do some other work here:
// ...
for(int i = 0; i < 10; i++)
Console.Write("Working... ");
var result =
t.ContinueWith((antecedent) =>
{
// Error handling omitted...
return new UTF8Encoding().GetString(buffer);
});
// Can also do some other work here:
// ...
for (int i = 0; i < 10; i++)
Console.Write("Working more... ");
try
{
t.Wait();
Console.WriteLine(result.Result.Substring(0, 50));
}
catch (AggregateException ae)
{
Console.WriteLine(ae.InnerException.Message);
}
//</snippet13>
Console.ReadLine();
}
// nested dummy class for snippet0 5 below
class MyCustomState
{
public string StateData { get; set; }
public MyCustomState() { StateData = "Hello"; }
}
private MyCustomState GetCustomState()
{
return new MyCustomState();
}
//<snippet05>
public Task<string> GetFileStringAsync2(string path)
{
FileInfo fi = new FileInfo(path);
byte[] data = new byte[fi.Length];
MyCustomState state = GetCustomState();
FileStream fs = new FileStream(path, FileMode.Open, FileAccess.Read, FileShare.Read, data.Length, true);
// We still pass null for the last parameter because
// the state variable is visible to the continuation delegate.
Task<int> task = Task<int>.Factory.FromAsync(
fs.BeginRead, fs.EndRead, data, 0, data.Length, null);
return task.ContinueWith((antecedent) =>
{
// It is safe to close the filestream now.
fs.Close();
// Capture custom state data directly in the user delegate.
// No need to pass it through the FromAsync method.
if (state.StateData.Contains("New York, New York"))
{
return "Start spreading the news!";
}
else
{
// If we did not receive the entire file, the end of the
// data buffer will contain garbage.
if (antecedent.Result < data.Length)
Array.Resize(ref data, antecedent.Result);
// Will be returned in the Result property of the Task<string>
// at some future point after the asynchronous file I/O operation completes.
return new UTF8Encoding().GetString(data);
}
});
}
//</snippet05>
string[] GetFilesToRead()
{
return new string[3] { "test.txt", "test1.txt", "test2.txt" };
}
//<snippet06>
public Task<string> GetMultiFileData(string[] filesToRead)
{
FileStream fs;
Task<string>[] tasks = new Task<string>[filesToRead.Length];
byte[] fileData = null;
for (int i = 0; i < filesToRead.Length; i++)
{
fileData = new byte[0x1000];
fs = new FileStream(filesToRead[i], FileMode.Open, FileAccess.Read, FileShare.Read, fileData.Length, true);
// By adding the continuation here, the
// Result of each task will be a string.
tasks[i] = Task<int>.Factory.FromAsync(
fs.BeginRead, fs.EndRead, fileData, 0, fileData.Length, null)
.ContinueWith((antecedent) =>
{
fs.Close();
// If we did not receive the entire file, the end of the
// data buffer will contain garbage.
if (antecedent.Result < fileData.Length)
Array.Resize(ref fileData, antecedent.Result);
// Will be returned in the Result property of the Task<string>
// at some future point after the asynchronous file I/O operation completes.
return new UTF8Encoding().GetString(fileData);
});
}
// Wait for all tasks to complete.
return Task<string>.Factory.ContinueWhenAll(tasks, (data) =>
{
// Propagate all exceptions and mark all faulted tasks as observed.
Task.WaitAll(data);
// Combine the results from all tasks.
StringBuilder sb = new StringBuilder();
foreach (var t in data)
{
sb.Append(t.Result);
}
// Final result to be returned eventually on the calling thread.
return sb.ToString();
});
}
//</snippet06>
public string ProcessData(Task[] arr)
{
return "processed";
}
//<snippet11>
void ProcessFilesAsync()
{
string[] files = Directory.GetFiles(@"\\remoteComputer\folderName\", "*.*", SearchOption.AllDirectories);
CancellationTokenSource cts = new CancellationTokenSource();
List<Task<string>> tasks = new List<Task<string>>();
foreach (var file in files)
{
Task<string> t = null;
try
{
t = GetFileStringAsync3(file, cts.Token);
}
catch
{
Console.WriteLine($"Argument exception on {file}");
continue;
}
t.ContinueWith((antecedent) => ProcessFileData(antecedent.Result));
tasks.Add(t);
}
Console.WriteLine("All tasks have been added.");
// Do some work here.
try
{
Task.WaitAll(tasks.ToArray());
Console.WriteLine("All tasks have completed.");
}
catch (AggregateException ae)
{
foreach (var ex in ae.InnerExceptions)
Console.WriteLine(ex.Message);
}
finally
{
cts.Dispose();
}
// If needed, perform a final step after all tasks have completed.
Task.Factory.ContinueWhenAll(tasks.ToArray(), (arr) =>
{
foreach (var t in arr)
{
CompareFileData(t.Result);
}
});
}
public Task<string> GetFileStringAsync3(string path, CancellationToken token)
{
if (!File.Exists(path))
{
throw new FileNotFoundException(String.Format("Could not find {0}", path));
}
FileInfo fi = new FileInfo(path);
byte[] data = null;
if (fi.Length < MAX_FILE_SIZE && fi.Length > 0)
{
data = new byte[fi.Length];
}
else
{
throw new ArgumentException(String.Format("{0} is too big to load!", path));
}
FileStream fs = new FileStream(path, FileMode.Open, FileAccess.Read, FileShare.Read, data.Length, true);
// We still pass null for the last parameter because
// the state variable is visible to the continuation delegate.
Task<int> task = Task<int>.Factory.FromAsync(
fs.BeginRead, fs.EndRead, data, 0, data.Length, null);
return task.ContinueWith((antecedent) =>
{
fs.Close();
// If we did not receive the entire file, the end of the
// data buffer will contain garbage.
if (antecedent.Result < data.Length)
Array.Resize(ref data, antecedent.Result);
// Will be returned in the Result property of the Task<string>
// at some future point after the asynchronous file I/O operation completes.
return new UTF8Encoding().GetString(data);
});
}
string ProcessFileData(string data)
{
string s = data.Substring(0, 80);
Console.WriteLine(s);
return s;
}
string CompareFileData(string s)
{
return "compare results";
}
//</snippet11>
}sample · vbsamples/snippets/visualbasic/VS_Snippets_Misc/fromasync/vb/module1.vb09
Imports System.Collections.Generic
Imports System.IO
Imports System.Net
Imports System.Text
Imports System.Threading
Imports System.Threading.Tasks
Namespace specialNamespaceForOneMethodSignature
Class Task(Of TResult)
Public TValue As TResult
End Class
Class Dummy(Of TResult)
'<snippet01>
Public Function FromAsync(Of TArg1, TArg2, TArg3)(
ByVal beginMethod As Func(Of TArg1, TArg2, TArg3, AsyncCallback, Object, IAsyncResult),
ByVal endMethod As Func(Of IAsyncResult, TResult),
ByVal dataBuffer As TArg1,
ByVal byteOffsetToStartAt As TArg2,
ByVal maxBytesToRead As TArg3,
ByVal stateInfo As Object)
'</snippet01>
Return New Task(Of TResult)
End Function
End Class
End Namespace
Module Module1
Class AsyncResult
Public Sub New()
End Sub
'<snippet07>
Shared Function ReturnTaskFromAsyncResult() As Task(Of String)
Dim ar As IAsyncResult = DoSomethingAsynchronously()
Dim t As Task(Of String) = Task(Of String).Factory.FromAsync(ar, Function(res) CStr(res.AsyncState))
Return t
End Function
'</snippet07>
Private Shared Function DoSomethingAsynchronously() As IAsyncResult
Throw New NotImplementedException
End Function
End Class
'<snippet08>
Class WebDataDownLoader
Dim tcs As New TaskCompletionSource(Of String())
Dim nameToSearch As String
Dim token As CancellationToken
Dim results As New List(Of String)
Dim m_lock As Object
Dim count As Integer
Dim addresses() As String
Shared Sub Main()
Dim downloader As New WebDataDownLoader()
downloader.addresses = {"http://www.msnbc.com", "http://www.yahoo.com", _
"http://www.nytimes.com", "http://www.washingtonpost.com", _
"http://www.latimes.com", "http://www.newsday.com"}
Dim cts As New CancellationTokenSource()
' Create a UI thread from which to cancel the entire operation
Task.Factory.StartNew(Sub()
Console.WriteLine("Press c to cancel")
If Console.ReadKey().KeyChar = "c"c Then
cts.Cancel()
End If
End Sub)
' Using a neutral search term that is sure to get some hits on English web sites.
' Please substitute your favorite search term.
downloader.nameToSearch = "the"
Dim webTask As Task(Of String()) = downloader.GetWordCounts(downloader.addresses, downloader.nameToSearch, cts.Token)
' Do some other work here unless the method has already completed.
If (webTask.IsCompleted = False) Then
' Simulate some work
Thread.SpinWait(5000000)
End If
Dim results As String() = Nothing
Try
results = webTask.Result
Catch ae As AggregateException
For Each ex As Exception In ae.InnerExceptions
If (TypeOf (ex) Is OperationCanceledException) Then
Dim oce As OperationCanceledException = CType(ex, OperationCanceledException)
If oce.CancellationToken = cts.Token Then
Console.WriteLine("Operation canceled by user.")
End If
Else
Console.WriteLine(ex.Message)
End If
Next
Finally
cts.Dispose()
End Try
If (Not results Is Nothing) Then
For Each item As String In results
Console.WriteLine(item)
Next
End If
Console.WriteLine("Press any key to exit")
Console.ReadKey()
End Sub
Public Function GetWordCounts(ByVal urls() As String, ByVal str As String, ByVal token As CancellationToken) As Task(Of String())
Dim webClients() As WebClient
ReDim webClients(urls.Length)
m_lock = New Object()
' If the user cancels the CancellationToken, then we can use the
' WebClient's ability to cancel its own async operations.
token.Register(Sub()
For Each wc As WebClient In webClients
If Not wc Is Nothing Then
wc.CancelAsync()
End If
Next
End Sub)
For i As Integer = 0 To urls.Length - 1
webClients(i) = New WebClient()
' Specify the callback for the DownloadStringCompleted
' event that will be raised by this WebClient instance.
AddHandler webClients(i).DownloadStringCompleted, AddressOf WebEventHandler
Dim address As Uri = Nothing
Try
address = New Uri(urls(i))
' Pass the address, and also use it for the userToken
' to identify the page when the delegate is invoked.
webClients(i).DownloadStringAsync(address, address)
Catch ex As UriFormatException
tcs.TrySetException(ex)
Return tcs.Task
End Try
Next
' Return the underlying Task. The client code
' waits on the Result property, and handles exceptions
' in the try-catch block there.
Return tcs.Task
End Function
Public Sub WebEventHandler(ByVal sender As Object, ByVal args As DownloadStringCompletedEventArgs)
If args.Cancelled = True Then
tcs.TrySetCanceled()
Return
ElseIf Not args.Error Is Nothing Then
tcs.TrySetException(args.Error)
Return
Else
' Split the string into an array of words,
' then count the number of elements that match
' the search term.
Dim words() As String = args.Result.Split(" "c)
Dim NAME As String = nameToSearch.ToUpper()
Dim nameCount = (From word In words.AsParallel()
Where word.ToUpper().Contains(NAME)
Select word).Count()
' Associate the results with the url, and add new string to the array that
' the underlying Task object will return in its Result property.
results.Add(String.Format("{0} has {1} instances of {2}", args.UserState, nameCount, nameToSearch))
End If
SyncLock (m_lock)
count = count + 1
If (count = addresses.Length) Then
tcs.TrySetResult(results.ToArray())
End If
End SyncLock
End Sub
'</snippet08>
End Class
'<snippet09>
Class Calculator
Public Function BeginCalculate(ByVal decimalPlaces As Integer, ByVal ac As AsyncCallback, ByVal state As Object) As IAsyncResult
Console.WriteLine("Calling BeginCalculate on thread {0}", Thread.CurrentThread.ManagedThreadId)
Dim myTask = Task(Of String).Factory.StartNew(Function(obj) Compute(decimalPlaces), state)
myTask.ContinueWith(Sub(antecedent) ac(myTask))
End Function
Private Function Compute(ByVal decimalPlaces As Integer)
Console.WriteLine("Calling compute on thread {0}", Thread.CurrentThread.ManagedThreadId)
' Simulating some heavy work.
Thread.SpinWait(500000000)
' Actual implementation left as exercise for the reader.
' Several examples are available on the Web.
Return "3.14159265358979323846264338327950288"
End Function
Public Function EndCalculate(ByVal ar As IAsyncResult) As String
Console.WriteLine("Calling EndCalculate on thread {0}", Thread.CurrentThread.ManagedThreadId)
Return CType(ar, Task(Of String)).Result
End Function
End Class
Class CalculatorClient
Shared decimalPlaces As Integer
Shared Sub Main()
Dim calc As New Calculator
Dim places As Integer = 35
Dim callback As New AsyncCallback(AddressOf PrintResult)
Dim ar As IAsyncResult = calc.BeginCalculate(places, callback, calc)
' Do some work on this thread while the calculator is busy.
Console.WriteLine("Working...")
Thread.SpinWait(500000)
Console.ReadLine()
End Sub
Public Shared Sub PrintResult(ByVal result As IAsyncResult)
Dim c As Calculator = CType(result.AsyncState, Calculator)
Dim piString As String = c.EndCalculate(result)
Console.WriteLine("Calling PrintResult on thread {0}; result = {1}",
Thread.CurrentThread.ManagedThreadId, piString)
End Sub
End Class
'</snippet09>
Class FileStreamDemo
Shared Sub Main()
Dim fsd As New FileStreamDemo()
fsd.ShowCallingFromAsync()
End Sub
'<snippet03>
Const MAX_FILE_SIZE As Integer = 14000000
Shared Function GetFileStringAsync(ByVal path As String) As Task(Of String)
Dim fi As New FileInfo(path)
Dim data(fi.Length - 1) As Byte
Dim fs As FileStream = New FileStream(path, FileMode.Open, FileAccess.Read, FileShare.Read, data.Length, True)
' Task(Of Integer) returns the number of bytes read
Dim myTask As Task(Of Integer) = Task(Of Integer).Factory.FromAsync(
AddressOf fs.BeginRead, AddressOf fs.EndRead, data, 0, data.Length, Nothing)
' It is possible to do other work here while waiting
' for the antecedent task to complete.
' ...
' Add the continuation, which returns a Task<string>.
Return myTask.ContinueWith(Function(antecedent)
fs.Close()
If (antecedent.Result < 100) Then
Return "Data is too small to bother with."
End If
' If we did not receive the entire file, the end of the
' data buffer will contain garbage.
If (antecedent.Result < data.Length) Then
Array.Resize(data, antecedent.Result)
End If
' Will be returned in the Result property of the Task<string>
' at some future point after the asynchronous file I/O operation completes.
Return New UTF8Encoding().GetString(data)
End Function)
End Function
'</snippet03>
Public Sub ShowCallingFromAsync()
Dim path As String = "\\docbuild2\public\Main\Logs\DllDiffReport\DllDiffReport_BetweenInBuildAndInPublicShare.html"
'<snippet04>
Dim myTask As Task(Of String) = GetFileStringAsync(path)
' Do some other work
' ...
Try
Console.WriteLine(myTask.Result.Substring(0, 500))
Catch ex As AggregateException
Console.WriteLine(ex.InnerException.Message)
End Try
'</snippet04>
Console.WriteLine("Press Enter to exit.")
Console.ReadLine()
End Sub
'<snippet05>
Public Function GetFileStringAsync2(ByVal path As String) As Task(Of String)
Dim fi = New FileInfo(path)
Dim data(fi.Length - 1) As Byte
Dim state As New MyCustomState()
Dim fs As New FileStream(path, FileMode.Open, FileAccess.Read, FileShare.Read, data.Length, True)
' We still pass null for the last parameter because
' the state variable is visible to the continuation delegate.
Dim myTask As Task(Of Integer) = Task(Of Integer).Factory.FromAsync(
AddressOf fs.BeginRead, AddressOf fs.EndRead, data, 0, data.Length, Nothing)
Return myTask.ContinueWith(Function(antecedent)
fs.Close()
' Capture custom state data directly in the user delegate.
' No need to pass it through the FromAsync method.
If (state.StateData.Contains("New York, New York")) Then
Return "Start spreading the news!"
End If
' If we did not receive the entire file, the end of the
' data buffer will contain garbage.
If (antecedent.Result < data.Length) Then
Array.Resize(data, antecedent.Result)
End If
'/ Will be returned in the Result property of the Task<string>
'/ at some future point after the asynchronous file I/O operation completes.
Return New UTF8Encoding().GetString(data)
End Function)
End Function
'</snippet05>
'<snippet06>
Public Function GetMultiFileData(ByVal filesToRead As String()) As Task(Of String)
Dim fs As FileStream
Dim tasks(filesToRead.Length - 1) As Task(Of String)
Dim fileData() As Byte = Nothing
For i As Integer = 0 To filesToRead.Length
fileData(&H1000) = New Byte()
fs = New FileStream(filesToRead(i), FileMode.Open, FileAccess.Read, FileShare.Read, fileData.Length, True)
' By adding the continuation here, the
' Result of each task will be a string.
tasks(i) = Task(Of Integer).Factory.FromAsync(AddressOf fs.BeginRead,
AddressOf fs.EndRead,
fileData,
0,
fileData.Length,
Nothing).
ContinueWith(Function(antecedent)
fs.Close()
'If we did not receive the entire file, the end of the
' data buffer will contain garbage.
If (antecedent.Result < fileData.Length) Then
ReDim Preserve fileData(antecedent.Result)
End If
'Will be returned in the Result property of the Task<string>
' at some future point after the asynchronous file I/O operation completes.
Return New UTF8Encoding().GetString(fileData)
End Function)
Next
Return Task(Of String).Factory.ContinueWhenAll(tasks, Function(data)
' Propagate all exceptions and mark all faulted tasks as observed.
Task.WaitAll(data)
' Combine the results from all tasks.
Dim sb As New StringBuilder()
For Each t As Task(Of String) In data
sb.Append(t.Result)
Next
' Final result to be returned eventually on the calling thread.
Return sb.ToString()
End Function)
End Function
'</snippet06>
Class MyCustomState
Public StateData As String
Public Sub New()
StateData = "Hello"
End Sub
End Class
End Class
End ModuleUse the StreamExtensions sample code
The StreamExtensions.cs file, in the .NET Standard parallel extensions extras repository, contains several reference implementations that use Task objects for asynchronous file and network I/O.