System.Threading.WaitHandle.WaitAny Method

Waits for any of the elements in the specified array to receive a signal, using a 32-bit signed integer to specify the time interval, and specifying whether to exit the synchronization domain before the wait.


[System.Runtime.ConstrainedExecution.ReliabilityContract(System.Runtime.ConstrainedExecution.Consistency.WillNotCorruptState, System.Runtime.ConstrainedExecution.Cer.MayFail)]
public static int WaitAny (WaitHandle[] waitHandles, int millisecondsTimeout, bool exitContext)


A WaitHandle array containing the objects for which the current instance will wait.
The number of milliseconds to wait, or Timeout.Infinite (-1) to wait indefinitely.
true to exit the synchronization domain for the context before the wait (if in a synchronized context), and reacquire it afterward; otherwise, false.


The array index of the object that satisfied the wait, or WaitHandle.WaitTimeout if no object satisfied the wait and a time interval equivalent to millisecondsTimeout has passed.


If millisecondsTimeout is zero, the method does not block. It tests the state of the wait handles and returns immediately.

System.Threading.AbandonedMutexException is new in the .NET Framework version 2.0. In previous versions, the erload:System.Threading.WaitHandle.WaitAny method returns true if the wait completes because a mutex is abandoned. An abandoned mutex often indicates a serious coding error. In the case of a system-wide mutex, it might indicate that an application has been terminated abruptly (for example, by using Windows Task Manager). The exception contains information useful for debugging.

The erload:System.Threading.WaitHandle.WaitAny method throws an System.Threading.AbandonedMutexException only when the wait completes because of an abandoned mutex. If waitHandles contains a released mutex with a lower index number than the abandoned mutex, the erload:System.Threading.WaitHandle.WaitAny method completes normally and the exception is not thrown.


In versions of the .NET Framework earlier than version 2.0, if a thread exits or aborts without explicitly releasing a System.Threading.Mutex, and that Mutex is at index 0 (zero) in a WaitAny array on another thread, the index returned by WaitAny is 128 instead of 0.

This method returns when the wait terminates, either when any of the handles are signaled or when a timeout occurs. If more than one object becomes signaled during the call, the return value is the array index of the signaled object with the smallest index value of all the signaled objects. On some implementations, if more that 64 handles are passed, a NotSupportedException is thrown.

Notes on Exiting the Context

The exitContext parameter has no effect unless the WaitHandle.WaitAny(WaitHandle[], int, bool) method is called from inside a nondefault managed context. This can happen if your thread is inside a call to an instance of a class derived from ContextBoundObject. Even if you are currently executing a method on a class that does not derive from ContextBoundObject, like string, you can be in a nondefault context if a ContextBoundObject is on your stack in the current application domain.

When your code is executing in a nondefault context, specifying true for exitContext causes the thread to exit the nondefault managed context (that is, to transition to the default context) before executing the WaitHandle.WaitAny(WaitHandle[], int, bool) method. The thread returns to the original nondefault context after the call to the WaitHandle.WaitAny(WaitHandle[], int, bool) method completes.

This can be useful when the context-bound class has System.Runtime.Remoting.Contexts.SynchronizationAttribute. In that case, all calls to members of the class are automatically synchronized, and the synchronization domain is the entire body of code for the class. If code in the call stack of a member calls the WaitHandle.WaitAny(WaitHandle[], int, bool) method and specifies true for exitContext, the thread exits the synchronization domain, allowing a thread that is blocked on a call to any member of the object to proceed. When the WaitHandle.WaitAny(WaitHandle[], int, bool) method returns, the thread that made the call must wait to reenter the synchronization domain.


Namespace: System.Threading
Assembly: mscorlib (in mscorlib.dll)
Assembly Versions: 1.0.5000.0,,