WaitHandle.WaitOne Method (Int32, Boolean)

When overridden in a derived class, blocks the current thread until the current WaitHandle receives a signal, using 32-bit signed integer to measure the time interval and specifying whether to exit the synchronization domain before the wait.

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

virtual bool WaitOne (
	int millisecondsTimeout, 
	bool exitContext
public boolean WaitOne (
	int millisecondsTimeout, 
	boolean exitContext
public function WaitOne (
	millisecondsTimeout : int, 
	exitContext : boolean
) : boolean



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


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

true if the current instance receives a signal; otherwise, false.

Exception typeCondition


The current instance has already been disposed.


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.

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

The caller of this method blocks until the current instance receives a signal or a time-out occurs. Use this method to block until a WaitHandle receives a signal from another thread, such as is generated when an asynchronous operation completes. For more information, see the IAsyncResult interface.

Override this method to customize the behavior of derived classes.

Notes on Exiting the Context

The exitContext parameter has no effect unless the WaitOne 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 WaitOne method. The thread returns to the original nondefault context after the call to the WaitOne 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 WaitOne 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 WaitOne method returns, the thread that made the call must wait to reenter the synchronization domain.

The following code example shows how to use a wait handle to keep a process from terminating while it waits for a background thread to finish executing.

using namespace System;
using namespace System::Threading;
ref class WaitOne

   static void WorkMethod( Object^ stateInfo )
      Console::WriteLine( "Work starting." );
      // Simulate time spent working.
      Thread::Sleep( (gcnew Random)->Next( 100, 2000 ) );
      // Signal that work is finished.
      Console::WriteLine( "Work ending." );


int main()
   Console::WriteLine( "Main starting." );
   AutoResetEvent^ autoEvent = gcnew AutoResetEvent( false );
   ThreadPool::QueueUserWorkItem( gcnew WaitCallback( &WaitOne::WorkMethod ), autoEvent );
   // Wait for work method to signal.
   if ( autoEvent->WaitOne( 1000, false ) )
      Console::WriteLine( "Work method signaled." );
      Console::WriteLine( "Timed out waiting for work "
      "method to signal." );

   Console::WriteLine( "Main ending." );

import System.*;
import System.Threading.*;
import System.Threading.Thread;

class WaitOne
    private static AutoResetEvent autoEvent = new AutoResetEvent(false);

    public static void main(String[] args)
        Console.WriteLine("Main starting.");
        ThreadPool.QueueUserWorkItem(new WaitCallback(WorkMethod), autoEvent);

        // Wait for work method to signal.
        if (autoEvent.WaitOne(1000, false)) {
            Console.WriteLine("Work method signaled.");
        else {
            Console.WriteLine(("Timed out waiting for work " 
                + "method to signal."));
        Console.WriteLine("Main ending.");
    } //main

    static void WorkMethod(Object stateInfo)
        Console.WriteLine("Work starting.");

        // Simulate time spent working.
        Thread.Sleep((new Random()).Next(100, 2000));

        // Signal that work is finished.
        Console.WriteLine("Work ending.");
    } //WorkMethod
} //WaitOne

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

.NET Compact Framework

Supported in: 2.0

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