ThreadState Enumeration

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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)

[SerializableAttribute]
[FlagsAttribute]
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.

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.

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

Action

ThreadState

A thread is created within the common language runtime.

Unstarted

A thread calls Start

Unstarted

The thread starts running.

Running

The thread calls Sleep

WaitSleepJoin

The thread calls Wait on another object.

WaitSleepJoin

The thread calls Join on another thread.

WaitSleepJoin

Another thread calls Interrupt

Running

Another thread calls Suspend

SuspendRequested

The thread responds to a Suspend request.

Suspended

Another thread calls Resume

Running

Another thread calls Abort

AbortRequested

The thread responds to a Abort request.

Stopped

A thread is terminated.

Stopped

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.

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