The System.Threading.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.

System.Threading.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 Thread.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.

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 Monitor.Wait(object, int, bool), and another thread calls Thread.Abort(object) 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 Monitor.Wait(object, int, bool) or is interrupted, it will receive the System.Threading.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.