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WaitHandle.WaitOne Method (Int32, Boolean)

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)

public virtual bool WaitOne (
	int millisecondsTimeout,
	bool exitContext
)
public boolean WaitOne (
	int millisecondsTimeout, 
	boolean exitContext
)
public function WaitOne (
	millisecondsTimeout : int, 
	exitContext : boolean
) : boolean
Not applicable.

Parameters

millisecondsTimeout

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

exitContext

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

ObjectDisposedException

The current instance has already been disposed.

ArgumentOutOfRangeException

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

AbandonedMutexException

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

InvalidOperationException

The current instance is 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 handle and returns immediately.

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 often indicates a serious coding error. In the case of a system-wide mutex, it might indicate that an application has been terminated abruptly (for example, by using Windows Task Manager). 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 System;
using System.Threading;

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

    static void Main()
    {
        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.");
    }

    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.");
        ((AutoResetEvent)stateInfo).Set();
    }
}

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.");
        ((AutoResetEvent)(stateInfo)).Set();
    } //WorkMethod
} //WaitOne

Windows 98, Windows Server 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 Microsoft .NET Framework 3.0 is supported on Windows Vista, Microsoft Windows XP SP2, and Windows Server 2003 SP1.

.NET Framework

Supported in: 3.0, 2.0, 1.1, 1.0

.NET Compact Framework

Supported in: 2.0

XNA Framework

Supported in: 1.0
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