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ThreadPool.UnsafeRegisterWaitForSingleObject Method (WaitHandle, WaitOrTimerCallback, Object, UInt32, Boolean)

Registers a delegate to wait for a WaitHandle, specifying a 32-bit unsigned integer for the time-out in milliseconds. This method does not propagate the calling stack to the worker thread.

This API is not CLS-compliant. 

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

[CLSCompliantAttribute(false)]
public static RegisteredWaitHandle UnsafeRegisterWaitForSingleObject(
	WaitHandle waitObject,
	WaitOrTimerCallback callBack,
	Object state,
	uint millisecondsTimeOutInterval,
	bool executeOnlyOnce
)

Parameters

waitObject
Type: System.Threading.WaitHandle

The WaitHandle to register. Use a WaitHandle other than Mutex.

callBack
Type: System.Threading.WaitOrTimerCallback

The delegate to call when the waitObject parameter is signaled.

state
Type: System.Object

The object that is passed to the delegate.

millisecondsTimeOutInterval
Type: System.UInt32

The time-out in milliseconds. If the millisecondsTimeOutInterval parameter is 0 (zero), the function tests the object's state and returns immediately. If millisecondsTimeOutInterval is -1, the function's time-out interval never elapses.

executeOnlyOnce
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 RegisteredWaitHandle object that can be used to cancel the registered wait operation.

ExceptionCondition
SecurityException

The caller does not have the required permission.

Unlike the RegisterWaitForSingleObject method, UnsafeRegisterWaitForSingleObject does not propagate the calling stack to the worker thread. This allows code to lose the calling stack and thereby to elevate its security privileges.

Caution noteCaution

Using UnsafeRegisterWaitForSingleObject could inadvertently open up a security hole. Code access security bases its permission checks on the permissions of all the callers on the stack. When work is queued on a thread pool thread using UnsafeRegisterWaitForSingleObject, the stack of the thread pool thread will not have the context of the actual callers. Malicious code might be able exploit this to avoid permission checks.

Using a Mutex for waitObject does not provide mutual exclusion for the callbacks because the underlying Win32 API uses the default WT_EXECUTEDEFAULT flag, so each callback is dispatched on a separate thread pool thread.

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.

.NET Framework

Supported in: 4.6, 4.5, 4, 3.5, 3.0, 2.0, 1.1, 1.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

  • SecurityCriticalAttribute 

    Requires full trust for the immediate caller. This member cannot be used by partially trusted or transparent code.

Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

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

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