ThreadPool.RegisterWaitForSingleObject Method (WaitHandle, WaitOrTimerCallback, Object, TimeSpan, Boolean)

Registers a delegate to wait for a WaitHandle, specifying a TimeSpan value for the time-out.

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

<SecuritySafeCriticalAttribute> _
Public Shared Function RegisterWaitForSingleObject ( _
	waitObject As WaitHandle, _
	callBack As WaitOrTimerCallback, _
	state As Object, _
	timeout As TimeSpan, _
	executeOnlyOnce As Boolean _
) As RegisteredWaitHandle


Type: System.Threading.WaitHandle
The wait handle to register.
Type: System.Threading.WaitOrTimerCallback
The delegate to call when the waitObject parameter is signaled.
Type: System.Object
The object passed to the delegate.
Type: System.TimeSpan
The time-out represented by a TimeSpan. If timeout is 0 (zero), the function tests the object's state and returns immediately. If timeout is -1, the function's time-out interval never elapses.
Type: System.Boolean
true to indicate that the thread will no longer wait on the waitObject parameter after the delegate has been called; false to indicate that the timer is reset every time the wait operation completes until the wait is unregistered.

Return Value

Type: System.Threading.RegisteredWaitHandle
The registered wait handle.


The timeout parameter is less than -1.


The timeout parameter is greater than Int32.MaxValue.

When you are finished using the RegisteredWaitHandle that is returned by this method, call its RegisteredWaitHandle.Unregister method to release references to the wait handle. We recommend that you always call the RegisteredWaitHandle.Unregister method, even if you specify true for executeOnlyOnce. Garbage collection works more efficiently if you call the RegisteredWaitHandle.Unregister method instead of depending on the registered wait handle's finalizer.

The RegisterWaitForSingleObject method queues the specified delegate to the thread pool. A worker thread will execute the delegate when one of the following occurs:

  • The specified object is in the signaled state.

  • The time-out interval elapses.

The RegisterWaitForSingleObject method checks the current state of the specified object's WaitHandle. If the object's state is unsignaled, the method registers a wait operation. The wait operation is performed by a thread from the thread pool. The delegate is executed by a worker thread when the object's state becomes signaled or the time-out interval elapses. If the timeOutInterval parameter is not 0 (zero) and the executeOnlyOnce parameter is false, the timer is reset every time the event is signaled or the time-out interval elapses.

Before returning, the method modifies the state of some types of synchronization objects. Modification occurs only for the object whose signaled state caused the wait condition to be satisfied.

Version Notes

Silverlight for Windows Phone Silverlight for Windows Phone

When a user navigates away from a Windows Phone application, the application is typically put into a dormant state. When the user returns to a dormant application, the application automatically resumes. If the application is put into a dormant state while this API is being used, the API will not complete as expected. Applications should be designed to handle this possibility. For more information about the Windows Phone execution model, see Execution Model for Windows Phone.


Supported in: 5, 4, 3

Silverlight for Windows Phone

Supported in: Windows Phone OS 7.1, Windows Phone OS 7.0

XNA Framework

Supported in: Xbox 360, Windows Phone OS 7.0

For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.

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