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WaitHandle.SignalAndWait Method (WaitHandle, WaitHandle, Int32, Boolean)

Updated: April 2011

Signals one WaitHandle and waits on another, specifying a time-out interval as a 32-bit signed integer and specifying whether to exit the synchronization domain for the context before entering the wait.

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

public static bool SignalAndWait(
	WaitHandle toSignal,
	WaitHandle toWaitOn,
	int millisecondsTimeout,
	bool exitContext


Type: System.Threading.WaitHandle
The WaitHandle to signal.
Type: System.Threading.WaitHandle
The WaitHandle to wait on.
Type: System.Int32
An integer that represents the interval to wait. If the value is Timeout.Infinite, that is, -1, the wait is infinite.
Type: System.Boolean
true to exit the synchronization domain for the context before the wait (if in a synchronized context), and reacquire it afterward; otherwise, false.

Return Value

Type: System.Boolean
true if both the signal and the wait completed successfully, or false if the signal completed but the wait timed out.


toSignal is null.


toWaitOn is null.


The method is called on a thread that has STAThreadAttribute.


This method is not supported on Windows 98 or Windows Millennium Edition.


toSignal is a semaphore, and it already has a full count.


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 WaitHandle cannot be signaled because it would exceed its maximum count.

This operation is not guaranteed to be atomic. After the current thread signals toSignal but before it waits on toWaitOn, a thread that is running on another processor might signal toWaitOn or wait on it.

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

Notes on Exiting the Context

The exitContext parameter has no effect unless the SignalAndWait 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 SignalAndWait method. The thread returns to the original nondefault context after the call to the SignalAndWait method completes.

This can be useful when the context-bound class has 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 SignalAndWait 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 SignalAndWait method returns, the thread that made the call must wait to reenter the synchronization domain.

.NET Framework

Supported in: 4, 3.5, 3.0, 2.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

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




April 2011

Correction: The operation is not atomic.

Customer feedback.