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WaitHandle.WaitAll Method (WaitHandle[], Int32)


Waits for all the elements in the specified array to receive a signal, using an Int32 value to specify the time interval.

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

public static bool WaitAll(
	WaitHandle[] waitHandles,
	int millisecondsTimeout


Type: System.Threading.WaitHandle[]

A WaitHandle array containing the objects for which the current instance will wait. This array cannot contain multiple references to the same object (duplicates).

Type: System.Int32

The number of milliseconds to wait, or Timeout.Infinite (-1) to wait indefinitely.

Return Value

Type: System.Boolean

true when every element in waitHandles has received a signal; otherwise, false.

Exception Condition

The waitHandles parameter is null.


One or more of the objects in the waitHandles array is null.


waitHandles is an array with no elements.


In the .NET for Windows Store apps or the , catch the base class exception, ArgumentException, instead.

The waitHandles array contains elements that are duplicates.


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


The STAThreadAttribute attribute is applied to the thread procedure for the current thread, and waitHandles contains more than one element.


millisecondsTimeout is a negative number other than -1, which represents an infinite time-out.


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


The waitHandles array contains a transparent proxy for a WaitHandle in another application domain.

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

The WaitAll method returns when the wait terminates, which means either when all the handles are signaled or when time-out occurs. On some implementations, if more than 64 handles are passed, a NotSupportedException is thrown. If there are duplicates in the array, the call fails with a DuplicateWaitObjectException.


The WaitAll method is not supported on threads that have STAThreadAttribute.

Calling this method overload is the same as calling the WaitAll(WaitHandle[], Int32, Boolean) overload and specifying false for exitContext.

Universal Windows Platform
Available since 4.5
.NET Framework
Available since 2.0
Portable Class Library
Supported in: portable .NET platforms
Available since 2.0
Windows Phone Silverlight
Available since 7.0
Windows Phone
Available since 8.1
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