WaitHandle.WaitAny Method (WaitHandle[])

Waits for any of the elements in the specified array to receive a signal.

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

Public Shared Function WaitAny ( _
	waitHandles As WaitHandle() _
) As Integer
Dim waitHandles As WaitHandle()
Dim returnValue As Integer

returnValue = WaitHandle.WaitAny(waitHandles)
public static int WaitAny (
	WaitHandle[] waitHandles
public static function WaitAny (
	waitHandles : WaitHandle[]
) : int



A WaitHandle array containing the objects for which the current instance will wait.

Return Value

The array index of the object that satisfied the wait.

Exception typeCondition


The waitHandles parameter is a null reference (Nothing in Visual Basic) or one or more of the objects in the waitHandles array is a null reference (Nothing in Visual Basic).


The number of objects in waitHandles is greater than the system permits.


waitHandles is an array with no elements.


The wait completed because a thread exited without releasing a mutex. This exception is not thrown on Windows 98 or Windows Millennium Edition.

AbandonedMutexException is new in the .NET Framework version 2.0. In previous versions, the WaitAny method returns true if the wait completes because a mutex is abandoned. An abandoned mutex indicates a serious coding error. The exception contains information useful for debugging.

The WaitAny method throws an 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 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 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 any handle is signaled. 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.

Calling this method overload is equivalent to calling the WaitAny(WaitHandle[],Int32,Boolean) method overload and specifying -1 (or Timeout.Infinite) for millisecondsTimeout and true for exitContext.

The following code example demonstrates calling the WaitAny method. This code example is part of a larger example provided for the WaitHandle class.

<MTAThreadAttribute> _
Public Shared Sub Main() 
    ' Queue two tasks on two different threads; 
    ' wait until all tasks are completed.
    Dim dt As DateTime = DateTime.Now
    Console.WriteLine("Main thread is waiting for BOTH tasks to complete.")
    ThreadPool.QueueUserWorkItem(AddressOf DoTask, waitHandles(0))
    ThreadPool.QueueUserWorkItem(AddressOf DoTask, waitHandles(1))
    ' The time shown below should match the longest task.
    Console.WriteLine("Both tasks are completed (time waited={0})", _
        (DateTime.Now - dt).TotalMilliseconds)
    ' Queue up two tasks on two different threads; 
    ' wait until any tasks are completed.
    dt = DateTime.Now
    Console.WriteLine("The main thread is waiting for either task to complete.")
    ThreadPool.QueueUserWorkItem(AddressOf DoTask, waitHandles(0))
    ThreadPool.QueueUserWorkItem(AddressOf DoTask, waitHandles(1))
    Dim index As Integer = WaitHandle.WaitAny(waitHandles)
    ' The time shown below should match the shortest task.
    Console.WriteLine("Task {0} finished first (time waited={1}).", _
        index + 1,(DateTime.Now - dt).TotalMilliseconds)

End Sub 'Main

Windows 98, Windows 2000 SP4, Windows Millennium Edition, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition

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

.NET Framework

Supported in: 2.0, 1.1, 1.0