Using threads and threading

With .NET, you can write applications that perform multiple operations at the same time. Operations with the potential of holding up other operations can execute on separate threads, a process known as multithreading or free threading.

Applications that use multithreading are more responsive to user input because the user interface stays active as processor-intensive tasks execute on separate threads. Multithreading is also useful when you create scalable applications because you can add threads as the workload increases.

#How to: Create and start a new thread

You create a new thread by creating a new instance of the System.Threading.Thread class. You provide the name of the method that you want to execute on the new thread to the constructor. To start a created thread, call the System.Threading.Thread.Start method. For more information and examples, see the Creating threads and passing data at start time article and the System.Threading.Thread API reference.

#How to: Stop a thread

To terminate the execution of a thread, use the System.Threading.CancellationToken. It provides a unified way to stop threads cooperatively. For more information, see Cancellation in managed threads.

Sometimes it's not possible to stop a thread cooperatively because it runs third-party code not designed for cooperative cancellation. In this case, you might want to terminate its execution forcibly. In .NET Framework, you can use the System.Threading.Thread.Abort method, which raises a System.Threading.ThreadAbortException on the target thread. For more information, see Destroying threads.

In .NET Core and .NET 5 and later versions, System.Threading.Thread.Abort throws a System.PlatformNotSupportedException at runtime. In .NET 5 and later, calling it also generates a compile-time obsoletion warning (SYSLIB0006). If you need to terminate the execution of third-party code forcibly in modern .NET implementations, run it in a separate process and use the System.Diagnostics.Process.Kill method.

The System.Threading.CancellationToken isn't available before .NET Framework 4. To stop a thread in older .NET Framework versions, use the thread synchronization techniques to implement the cooperative cancellation manually. For example, you can create the volatile boolean field shouldStop and use it to request the code executed by the thread to stop. For more information, see volatile in C# Reference and System.Threading.Volatile.

Use the System.Threading.Thread.Join method to make the calling thread wait for the termination of the thread being stopped.

#How to: Pause or interrupt a thread

You use the System.Threading.Thread.Sleep method to pause the current thread for a specified amount of time. You can interrupt a blocked thread by calling the System.Threading.Thread.Interrupt method. For more information, see Pausing and interrupting threads.

#Thread properties

The following table presents some of the System.Threading.Thread properties:

#See also

• System.Threading.Thread
• Threads and Threading
• Parallel Programming