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WaitHandle.WaitOne Method ()

Blocks the current thread until the current WaitHandle receives a signal.

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

public virtual bool WaitOne ()
public boolean WaitOne ()
public function WaitOne () : boolean
Not applicable.

Return Value

true if the current instance receives a signal. If the current instance is never signaled, WaitOne never returns.

Exception typeCondition

ObjectDisposedException

The current instance has already been disposed.

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.

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 indefinitely until the current instance receives a signal. 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.

Calling this method overload is equivalent to calling the WaitOne(Int32,Boolean) method overload and specifying -1 or Timeout.Infinite for the first parameter and false for the second parameter.

Override this method to customize the behavior of derived classes.

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.
        autoEvent.WaitOne();
        Console.WriteLine("Work method signaled.\nMain 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.
        autoEvent.WaitOne();
        Console.WriteLine("Work method signaled.\nMain 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, 1.0

XNA Framework

Supported in: 1.0

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