WaitHandle.WaitOne Method (Int32, Boolean) (System.Threading)

WaitOne Method (Int32, Boolean)

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Microsoft Visual Studio 2008/.NET Framework 3.5

Other versions are also available for the following:

.NET Framework Class Library

WaitHandle..::.WaitOne Method (Int32, Boolean)

Blocks the current thread until the current WaitHandle receives a signal, using a 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)

Syntax

Visual Basic (Declaration)

Public Overridable Function WaitOne ( _
    millisecondsTimeout As Integer, _
    exitContext As Boolean _
) As Boolean

Visual Basic (Usage)

Dim instance As WaitHandle
Dim millisecondsTimeout As Integer
Dim exitContext As Boolean
Dim returnValue As Boolean

returnValue = instance.WaitOne(millisecondsTimeout, _
    exitContext)

public virtual bool WaitOne(
    int millisecondsTimeout,
    bool exitContext
)

Visual C++

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

JScript

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

Parameters

millisecondsTimeout: Type: System..::.Int32
The number of milliseconds to wait, or Timeout..::.Infinite (-1) to wait indefinitely.

exitContext: 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 the current instance receives a signal; otherwise, false.

Exceptions

Exception	Condition
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.

Remarks

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.

Examples

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.

Visual Basic

Imports System
Imports System.Threading

Public Class WaitOne

    Shared autoEvent As New AutoResetEvent(False)

    <MTAThread> _
    Shared Sub Main()
        Console.WriteLine("Main starting.")

        ThreadPool.QueueUserWorkItem(AddressOf WorkMethod, autoEvent)

        ' Wait for work method to signal.
        If autoEvent.WaitOne(1000, False) Then
            Console.WriteLine("Work method signaled.")
        Else
            Console.WriteLine("Timed out waiting for work " & _
                "method to signal.")
        End If

        Console.WriteLine("Main ending.")
    End Sub

    Shared Sub WorkMethod(stateInfo As Object) 
        Console.WriteLine("Work starting.")

        ' Simulate time spent working.
        Thread.Sleep(New Random().Next(100, 2000))

        ' Signal that work is finished.
        Console.WriteLine("Work ending.")
        CType(stateInfo, AutoResetEvent).Set()
    End Sub

End Class

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();
    }
}

Visual C++

using namespace System;
using namespace System::Threading;
ref class WaitOne
{
private:
   WaitOne(){}


public:
   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." );
      dynamic_cast<AutoResetEvent^>(stateInfo)->Set();
   }

};

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

Platforms

Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98, Windows CE, Windows Mobile for Smartphone, Windows Mobile for Pocket PC, Xbox 360

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

Version Information