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ThreadState Enumeration

[ This article is for Windows Phone 8 developers. If you’re developing for Windows 10, see the latest documentation. ]

Specifies the execution states of a Thread.

This enumeration has a FlagsAttribute attribute that allows a bitwise combination of its member values.

Namespace:  System.Threading
Assembly:  mscorlib (in mscorlib.dll)

public enum ThreadState

Member nameDescription
AbortedThe thread state includes AbortRequested and the thread is now dead, but its state has not yet changed to Stopped.
AbortRequestedThe Thread.Abort method has been invoked on the thread, but the thread has not yet received the pending System.Threading.ThreadAbortException that will attempt to terminate it.
BackgroundThe thread is being executed as a background thread, as opposed to a foreground thread. This state is controlled by setting the Thread.IsBackground property.
RunningThe thread has been started, it is not blocked, and there is no pending ThreadAbortException.
StoppedThe thread has stopped.
StopRequestedThe thread is being requested to stop. This is for internal use only.
SuspendedThe thread has been suspended.
SuspendRequestedThe thread has been marked for suspension.
UnstartedThe Thread.Start method has not been invoked on the thread.
WaitSleepJoinThe thread is blocked. This could be the result of calling Thread.Sleep or Thread.Join, of requesting a lock — for example, by calling Monitor.Enter or Monitor.Wait — or of waiting on a thread synchronization object such as ManualResetEvent.

ThreadState defines a set of all possible execution states for threads. Once a thread is created, it is in at least one of the states until it terminates. Threads that are created within the common language runtime are initially in the Unstarted state, whereas external threads that come into the runtime are already in the Running state. An Unstarted thread is transitioned into the Running state by calling the Start method. Not all combinations of ThreadState values are valid; for example, a thread cannot be in both the Aborted and Unstarted states.

Important noteImportant Note:

Thread state is of interest only in a few debugging scenarios. Your code should never use thread state to synchronize the activities of threads.

The following table shows the actions that cause a change of state.



A thread is created within the common language runtime.


The thread's Start method is called by another thread.


The thread starts running.


The thread calls Sleep.


The thread calls Wait or makes some other blocking call.


The thread calls Join on another thread.


The common language runtime marks the thread for suspension, for example, in order to do garbage collection.


The thread is suspended.


The thread resumes operation after being suspended.


Another thread calls Thread.Abort on the thread.


The thread is terminated.


The Thread.IsBackground property of the thread is set to true either by the thread itself or by another thread.


A thread can be in more than one state at a given time. For example:

  • The Background state can be combined with any other state.

  • If a thread is blocked on a call to Monitor.Wait and the system aborts it, the blocked thread will be in both the WaitSleepJoin and the AbortRequested states at the same time. In this case, as soon as the thread returns from the call to Wait or is interrupted, it will receive the ThreadAbortException and begin aborting.

The Thread.ThreadState property of a thread provides the current state of a thread. Applications must use a bitmask to determine whether a thread is running. Because the value for Running is 0 (zero), test whether a thread is running by using C# code such as (myThread.ThreadState & (ThreadState.Stopped | ThreadState.Unstarted)) == 0 or Visual Basic code such as (myThread.ThreadState And (ThreadState.Stopped Or ThreadState.Unstarted)) = 0.

Windows Phone OS

Supported in: 8.1, 8.0, 7.1, 7.0

Windows Phone