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.


If you need more control over the behavior of the application's threads, you can manage the threads yourself. However, multithreaded programming is greatly simplified with the System.Threading.Tasks.Parallel and System.Threading.Tasks.Task classes, Parallel LINQ (PLINQ), concurrent collection classes in the System.Collections.Concurrent namespace, and a programming model that's based on the concept of tasks rather than threads. For more information, see Parallel Programming and Task Parallel Library (TPL).

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 Thread.Start method. For more information and examples, see the Creating threads and passing data at start time article and the 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. To terminate the execution of a thread forcibly, in .NET Framework you can use the Thread.Abort method. That method raises a ThreadAbortException on the thread on which it's invoked. For more information, see Destroying threads. The Thread.Abort method isn't supported in .NET Core. If you need to terminate the execution of third-party code forcibly in .NET Core, run it in the separate process and use the 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 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 Thread.Sleep method to pause the current thread for a specified amount of time. You can interrupt a blocked thread by calling the Thread.Interrupt method. For more information, see Pausing and interrupting threads.

Thread properties

The following table presents some of the Thread properties:

Property Description
IsAlive Returns true if a thread has been started and hasn't yet terminated normally or aborted.
IsBackground Gets or sets a Boolean that indicates if a thread is a background thread. Background threads are like foreground threads. However, a background thread doesn't prevent a process from stopping. Once all foreground threads that belong to a process have stopped, the common language runtime ends the process by calling the Abort method on background threads that are still alive. For more information, see Foreground and Background Threads.
Name Gets or sets the name of a thread. Most frequently used to discover individual threads when you debug.
Priority Gets or sets a ThreadPriority value that's used by the operating system to prioritize thread scheduling. For more information, see Scheduling threads and the ThreadPriority reference.
ThreadState Gets a ThreadState value containing the current states of a thread.

See also