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ThreadState Enumeration

Updated: March 2011

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
RunningThe thread has been started, it is not blocked, and there is no pending ThreadAbortException.
StopRequestedThe thread is being requested to stop. This is for internal use only.
SuspendRequestedThe thread is being requested to suspend.
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.
UnstartedThe Thread.Start method has not been invoked on the thread.
StoppedThe thread has stopped.
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.
SuspendedThe thread has been suspended.
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.
AbortedThe thread state includes AbortRequested and the thread is now dead, but its state has not yet changed to Stopped.

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

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 created within the common language runtime are initially in the Unstarted state, while external threads that come into the runtime are already in the Running state. An Unstarted thread is transitioned into the Running state by calling Start. Not all combinations of ThreadState values are valid; for example, a thread cannot be in both the Aborted and Unstarted states.


There are two thread state enumerations, System.Threading.ThreadState and System.Diagnostics.ThreadState.

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



A thread is created within the common language runtime.


Another thread calls the Thread.Start method on the new thread, and the call returns.

The Start method does not return until the new thread has started running. There is no way to know at what point the new thread will start running during the call to Start.


The thread calls Sleep.


The thread calls Wait on another object.


The thread calls Join on another thread.


Another thread calls Interrupt.


Another thread calls Suspend.


The thread responds to a Suspend request.


Another thread calls Resume.


Another thread calls Abort.


The thread responds to a Abort request.


The thread is terminated.


In addition to the states noted above, there is also the Background state, which indicates whether the thread is running in the background or foreground.

A thread can be in more than one state at a given time. For example, if a thread is blocked on a call to Wait, and another thread calls Abort on the blocked thread, 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 to 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. Since the value for Running is zero (0), 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.

.NET Framework

Supported in: 4, 3.5, 3.0, 2.0, 1.1, 1.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.




March 2011

Clarified the relationship between the Thread.Start method and the Running state, and emphasized that the ThreadState enumeration should not be used to synchronize the activities of threads.

Content bug fix.