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WaitHandle.WaitOne Method

  • Reference

Definition

Namespace:
System.Threading
Assembly:
System.Runtime.dll
Assembly:
mscorlib.dll
Assembly:
netstandard.dll

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

Overloads

WaitOne()

Blocks the current thread until the current WaitHandle receives a signal.
WaitOne(Int32)

Blocks the current thread until the current WaitHandle receives a signal, using a 32-bit signed integer to specify the time interval in milliseconds.
WaitOne(TimeSpan)

Blocks the current thread until the current instance receives a signal, using a TimeSpan to specify the time interval.
WaitOne(Int32, Boolean)

Blocks the current thread until the current WaitHandle receives a signal, using a 32-bit signed integer to specify the time interval and specifying whether to exit the synchronization domain before the wait.
WaitOne(TimeSpan, Boolean)

Blocks the current thread until the current instance receives a signal, using a TimeSpan to specify the time interval and specifying whether to exit the synchronization domain before the wait.

WaitOne()

Source:
WaitHandle.cs
Source:
WaitHandle.cs
Source:
WaitHandle.cs

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

public:
 virtual bool WaitOne();
public virtual bool WaitOne ();
abstract member WaitOne : unit -> bool
override this.WaitOne : unit -> bool
Public Overridable Function WaitOne () As Boolean

Returns

Boolean

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

Exceptions

ObjectDisposedException

The current instance has already been disposed.

AbandonedMutexException

The wait completed because a thread exited without releasing a mutex.

InvalidOperationException

The current instance is a transparent proxy for a WaitHandle in another application 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.

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.
   autoEvent->WaitOne(  );
   Console::WriteLine( "Work method signaled.\nMain ending." );
}

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();
    }
}

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.
        autoEvent.WaitOne()
        Console.WriteLine("Work method signaled.")
        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

Remarks

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.

Applies to

WaitOne(Int32)

Source:
WaitHandle.cs
Source:
WaitHandle.cs
Source:
WaitHandle.cs

Blocks the current thread until the current WaitHandle receives a signal, using a 32-bit signed integer to specify the time interval in milliseconds.

public:
 virtual bool WaitOne(int millisecondsTimeout);
public virtual bool WaitOne (int millisecondsTimeout);
abstract member WaitOne : int -> bool
override this.WaitOne : int -> bool
Public Overridable Function WaitOne (millisecondsTimeout As Integer) As Boolean

Parameters

millisecondsTimeout
Int32

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

Returns

Boolean

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

Exceptions

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.

InvalidOperationException

The current instance is a transparent proxy for a WaitHandle in another application 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.

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 ) )
   {
      Console::WriteLine( "Work method signaled." );
   }
   else
   {
      Console::WriteLine( "Timed out waiting for work "
      "method to signal." );
   }

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

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))
        {
            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();
    }
}

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) 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

Remarks

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

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.

Calling this method overload is the same as calling the WaitOne(Int32, Boolean) overload and specifying false for exitContext.

Applies to

WaitOne(TimeSpan)

Source:
WaitHandle.cs
Source:
WaitHandle.cs
Source:
WaitHandle.cs

Blocks the current thread until the current instance receives a signal, using a TimeSpan to specify the time interval.

public:
 virtual bool WaitOne(TimeSpan timeout);
public virtual bool WaitOne (TimeSpan timeout);
abstract member WaitOne : TimeSpan -> bool
override this.WaitOne : TimeSpan -> bool
Public Overridable Function WaitOne (timeout As TimeSpan) As Boolean

Parameters

timeout
TimeSpan

A TimeSpan that represents the number of milliseconds to wait, or a TimeSpan that represents -1 milliseconds to wait indefinitely.

Returns

Boolean

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

Exceptions

ObjectDisposedException

The current instance has already been disposed.

ArgumentOutOfRangeException

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

-or-

timeout is greater than Int32.MaxValue.

AbandonedMutexException

The wait completed because a thread exited without releasing a mutex.

InvalidOperationException

The current instance is a transparent proxy for a WaitHandle in another application domain.

Remarks

If timeout is zero, the method does not block. It tests the state of the wait handle and returns immediately.

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.

The maximum value for timeout is Int32.MaxValue.

Calling this method overload is the same as calling the WaitOne(TimeSpan, Boolean) overload and specifying false for exitContext.

Applies to

WaitOne(Int32, Boolean)

Source:
WaitHandle.cs
Source:
WaitHandle.cs
Source:
WaitHandle.cs

Blocks the current thread until the current WaitHandle receives a signal, using a 32-bit signed integer to specify the time interval and specifying whether to exit the synchronization domain before the wait.

public:
 virtual bool WaitOne(int millisecondsTimeout, bool exitContext);
public virtual bool WaitOne (int millisecondsTimeout, bool exitContext);
abstract member WaitOne : int * bool -> bool
override this.WaitOne : int * bool -> bool
Public Overridable Function WaitOne (millisecondsTimeout As Integer, exitContext As Boolean) As Boolean

Parameters

millisecondsTimeout
Int32

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

exitContext
Boolean

true to exit the synchronization domain for the context before the wait (if in a synchronized context), and reacquire it afterward; otherwise, false.

Returns

Boolean

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

Exceptions

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.

InvalidOperationException

The current instance is a transparent proxy for a WaitHandle in another application domain.

Examples

The following example shows how the WaitOne(Int32, Boolean) method overload behaves when it is called within a synchronization domain. First, a thread waits with exitContext set to false and blocks until the wait timeout expires. A second thread executes after the first thread terminates and waits with exitContext set to true. The call to signal the wait handle for this second thread is not blocked, and the thread completes before the wait timeout.

using namespace System;
using namespace System::Threading;
using namespace System::Runtime::Remoting::Contexts;

[Synchronization(true)]
public ref class SyncingClass : ContextBoundObject
{
private:
    EventWaitHandle^ waitHandle;

public:
    SyncingClass()
    {
         waitHandle =
            gcnew EventWaitHandle(false, EventResetMode::ManualReset);
    }

    void Signal()
    {
        Console::WriteLine("Thread[{0:d4}]: Signalling...", Thread::CurrentThread->GetHashCode());
        waitHandle->Set();
    }

    void DoWait(bool leaveContext)
    {
        bool signalled;

        waitHandle->Reset();
        Console::WriteLine("Thread[{0:d4}]: Waiting...", Thread::CurrentThread->GetHashCode());
        signalled = waitHandle->WaitOne(3000, leaveContext);
        if (signalled)
        {
            Console::WriteLine("Thread[{0:d4}]: Wait released!!!", Thread::CurrentThread->GetHashCode());
        }
        else
        {
            Console::WriteLine("Thread[{0:d4}]: Wait timeout!!!", Thread::CurrentThread->GetHashCode());
        }
    }
};

public ref class TestSyncDomainWait
{
public:
    static void Main()
    {
        SyncingClass^ syncClass = gcnew SyncingClass();

        Thread^ runWaiter;

        Console::WriteLine("\nWait and signal INSIDE synchronization domain:\n");
        runWaiter = gcnew Thread(gcnew ParameterizedThreadStart(&TestSyncDomainWait::RunWaitKeepContext));
        runWaiter->Start(syncClass);
        Thread::Sleep(1000);
        Console::WriteLine("Thread[{0:d4}]: Signal...", Thread::CurrentThread->GetHashCode());
        // This call to Signal will block until the timeout in DoWait expires.
        syncClass->Signal();
        runWaiter->Join();

        Console::WriteLine("\nWait and signal OUTSIDE synchronization domain:\n");
        runWaiter = gcnew Thread(gcnew ParameterizedThreadStart(&TestSyncDomainWait::RunWaitLeaveContext));
        runWaiter->Start(syncClass);
        Thread::Sleep(1000);
        Console::WriteLine("Thread[{0:d4}]: Signal...", Thread::CurrentThread->GetHashCode());
        // This call to Signal is unblocked and will set the wait handle to
        // release the waiting thread.
        syncClass->Signal();
        runWaiter->Join();
    }

    static void RunWaitKeepContext(Object^ parm)
    {
        ((SyncingClass^)parm)->DoWait(false);
    }

    static void RunWaitLeaveContext(Object^ parm)
    {
        ((SyncingClass^)parm)->DoWait(true);
    }
};

int main()
{
    TestSyncDomainWait::Main();
}
// The output for the example program will be similar to the following:
//
// Wait and signal INSIDE synchronization domain:
//
// Thread[0004]: Waiting...
// Thread[0001]: Signal...
// Thread[0004]: Wait timeout!!!
// Thread[0001]: Signalling...
//
// Wait and signal OUTSIDE synchronization domain:
//
// Thread[0006]: Waiting...
// Thread[0001]: Signal...
// Thread[0001]: Signalling...
// Thread[0006]: Wait released!!!

using System;
using System.Threading;
using System.Runtime.Remoting.Contexts;

[Synchronization(true)]
public class SyncingClass : ContextBoundObject
{
    private EventWaitHandle waitHandle;

    public SyncingClass()
    {
         waitHandle =
            new EventWaitHandle(false, EventResetMode.ManualReset);
    }

    public void Signal()
    {
        Console.WriteLine("Thread[{0:d4}]: Signalling...", Thread.CurrentThread.GetHashCode());
        waitHandle.Set();
    }

    public void DoWait(bool leaveContext)
    {
        bool signalled;

        waitHandle.Reset();
        Console.WriteLine("Thread[{0:d4}]: Waiting...", Thread.CurrentThread.GetHashCode());
        signalled = waitHandle.WaitOne(3000, leaveContext);
        if (signalled)
        {
            Console.WriteLine("Thread[{0:d4}]: Wait released!!!", Thread.CurrentThread.GetHashCode());
        }
        else
        {
            Console.WriteLine("Thread[{0:d4}]: Wait timeout!!!", Thread.CurrentThread.GetHashCode());
        }
    }
}

public class TestSyncDomainWait
{
    public static void Main()
    {
        SyncingClass syncClass = new SyncingClass();

        Thread runWaiter;

        Console.WriteLine("\nWait and signal INSIDE synchronization domain:\n");
        runWaiter = new Thread(RunWaitKeepContext);
        runWaiter.Start(syncClass);
        Thread.Sleep(1000);
        Console.WriteLine("Thread[{0:d4}]: Signal...", Thread.CurrentThread.GetHashCode());
        // This call to Signal will block until the timeout in DoWait expires.
        syncClass.Signal();
        runWaiter.Join();

        Console.WriteLine("\nWait and signal OUTSIDE synchronization domain:\n");
        runWaiter = new Thread(RunWaitLeaveContext);
        runWaiter.Start(syncClass);
        Thread.Sleep(1000);
        Console.WriteLine("Thread[{0:d4}]: Signal...", Thread.CurrentThread.GetHashCode());
        // This call to Signal is unblocked and will set the wait handle to
        // release the waiting thread.
        syncClass.Signal();
        runWaiter.Join();
    }

    public static void RunWaitKeepContext(object parm)
    {
        ((SyncingClass)parm).DoWait(false);
    }

    public static void RunWaitLeaveContext(object parm)
    {
        ((SyncingClass)parm).DoWait(true);
    }
}

// The output for the example program will be similar to the following:
//
// Wait and signal INSIDE synchronization domain:
//
// Thread[0004]: Waiting...
// Thread[0001]: Signal...
// Thread[0004]: Wait timeout!!!
// Thread[0001]: Signalling...
//
// Wait and signal OUTSIDE synchronization domain:
//
// Thread[0006]: Waiting...
// Thread[0001]: Signal...
// Thread[0001]: Signalling...
// Thread[0006]: Wait released!!!

Imports System.Threading
Imports System.Runtime.Remoting.Contexts

<Synchronization(true)>
Public Class SyncingClass
    Inherits ContextBoundObject
    
    Private waitHandle As EventWaitHandle

    Public Sub New()
         waitHandle = New EventWaitHandle(false, EventResetMode.ManualReset)
    End Sub

    Public Sub Signal()
        Console.WriteLine("Thread[{0:d4}]: Signalling...", Thread.CurrentThread.GetHashCode())
        waitHandle.Set()
    End Sub

    Public Sub DoWait(leaveContext As Boolean)
        Dim signalled As Boolean

        waitHandle.Reset()
        Console.WriteLine("Thread[{0:d4}]: Waiting...", Thread.CurrentThread.GetHashCode())
        signalled = waitHandle.WaitOne(3000, leaveContext)
        If signalled Then
            Console.WriteLine("Thread[{0:d4}]: Wait released!!!", Thread.CurrentThread.GetHashCode())
        Else
            Console.WriteLine("Thread[{0:d4}]: Wait timeout!!!", Thread.CurrentThread.GetHashCode())
        End If
    End Sub
End Class

Public Class TestSyncDomainWait
    Public Shared Sub Main()
        Dim syncClass As New SyncingClass()

        Dim runWaiter As Thread

        Console.WriteLine(Environment.NewLine + "Wait and signal INSIDE synchronization domain:" + Environment.NewLine)
        runWaiter = New Thread(AddressOf RunWaitKeepContext)
        runWaiter.Start(syncClass)
        Thread.Sleep(1000)
        Console.WriteLine("Thread[{0:d4}]: Signal...", Thread.CurrentThread.GetHashCode())
        ' This call to Signal will block until the timeout in DoWait expires.
        syncClass.Signal()
        runWaiter.Join()

        Console.WriteLine(Environment.NewLine + "Wait and signal OUTSIDE synchronization domain:" + Environment.NewLine)
        runWaiter = New Thread(AddressOf RunWaitLeaveContext)
        runWaiter.Start(syncClass)
        Thread.Sleep(1000)
        Console.WriteLine("Thread[{0:d4}]: Signal...", Thread.CurrentThread.GetHashCode())
        ' This call to Signal is unblocked and will set the wait handle to
        ' release the waiting thread.
        syncClass.Signal()
        runWaiter.Join()
    End Sub

    Public Shared Sub RunWaitKeepContext(parm As Object)
        Dim syncClass As SyncingClass = CType(parm, SyncingClass)
        syncClass.DoWait(False)
    End Sub

    Public Shared Sub RunWaitLeaveContext(parm As Object)
        Dim syncClass As SyncingClass = CType(parm, SyncingClass)
        syncClass.DoWait(True)
    End Sub
End Class

' The output for the example program will be similar to the following:
'
' Wait and signal INSIDE synchronization domain:
'
' Thread[0004]: Waiting...
' Thread[0001]: Signal...
' Thread[0004]: Wait timeout!!!
' Thread[0001]: Signalling...
'
' Wait and signal OUTSIDE synchronization domain:
'
' Thread[0006]: Waiting...
' Thread[0001]: Signal...
' Thread[0001]: Signalling...
' Thread[0006]: Wait released!!!

Remarks

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

If a mutex is abandoned, an AbandonedMutexException is thrown. 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.

Exiting the context

The exitContext parameter has no effect unless this method is called from inside a nondefault managed context. The managed context can be nondefault if your thread is inside a call to an instance of a class derived from ContextBoundObject. Even if you're currently executing a method on a class that isn't derived 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 this method. The thread returns to the original nondefault context after the call to this method completes.

Exiting the context can be useful when the context-bound class has the SynchronizationAttribute attribute. 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 this method and specifies true for exitContext, the thread exits the synchronization domain, which allows a thread that's blocked on a call to any member of the object to proceed. When this method returns, the thread that made the call must wait to reenter the synchronization domain.

Applies to

WaitOne(TimeSpan, Boolean)

Source:
WaitHandle.cs
Source:
WaitHandle.cs
Source:
WaitHandle.cs

Blocks the current thread until the current instance receives a signal, using a TimeSpan to specify the time interval and specifying whether to exit the synchronization domain before the wait.

public:
 virtual bool WaitOne(TimeSpan timeout, bool exitContext);
public virtual bool WaitOne (TimeSpan timeout, bool exitContext);
abstract member WaitOne : TimeSpan * bool -> bool
override this.WaitOne : TimeSpan * bool -> bool
Public Overridable Function WaitOne (timeout As TimeSpan, exitContext As Boolean) As Boolean

Parameters

timeout
TimeSpan

A TimeSpan that represents the number of milliseconds to wait, or a TimeSpan that represents -1 milliseconds to wait indefinitely.

exitContext
Boolean

true to exit the synchronization domain for the context before the wait (if in a synchronized context), and reacquire it afterward; otherwise, false.

Returns

Boolean

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

Exceptions

ObjectDisposedException

The current instance has already been disposed.

ArgumentOutOfRangeException

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

-or-

timeout is greater than Int32.MaxValue.

AbandonedMutexException

The wait completed because a thread exited without releasing a mutex.

InvalidOperationException

The current instance is a transparent proxy for a WaitHandle in another application 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.

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( TimeSpan(0,0,1), false ) )
   {
      Console::WriteLine( "Work method signaled." );
   }
   else
   {
      Console::WriteLine( "Timed out waiting for work "
      "method to signal." );
   }

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

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(new TimeSpan(0, 0, 1), 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();
    }
}

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(New TimeSpan(0, 0, 1), 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

Remarks

If timeout is zero, the method does not block. It tests the state of the wait handle and returns immediately.

If a mutex is abandoned, an AbandonedMutexException is thrown. 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.

The maximum value for timeout is Int32.MaxValue.

Exiting the context

The exitContext parameter has no effect unless this method is called from inside a nondefault managed context. The managed context can be nondefault if your thread is inside a call to an instance of a class derived from ContextBoundObject. Even if you're currently executing a method on a class that isn't derived 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 this method. The thread returns to the original nondefault context after the call to this method completes.

Exiting the context can be useful when the context-bound class has the SynchronizationAttribute attribute. 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 this method and specifies true for exitContext, the thread exits the synchronization domain, which allows a thread that's blocked on a call to any member of the object to proceed. When this method returns, the thread that made the call must wait to reenter the synchronization domain.

Applies to