WaitHandle.SignalAndWait Method

Definition

Namespace:

System.Threading

Assembly:

System.Runtime.dll

Signals one WaitHandle and waits on another.

Overloads

SignalAndWait(WaitHandle, WaitHandle)	Signals one WaitHandle and waits on another.
SignalAndWait(WaitHandle, WaitHandle, Int32, Boolean)	Signals one WaitHandle and waits on another, specifying a time-out interval as a 32-bit signed integer and specifying whether to exit the synchronization domain for the context before entering the wait.
SignalAndWait(WaitHandle, WaitHandle, TimeSpan, Boolean)	Signals one WaitHandle and waits on another, specifying the time-out interval as a TimeSpan and specifying whether to exit the synchronization domain for the context before entering the wait.

SignalAndWait(WaitHandle, WaitHandle)

Source:

WaitHandle.cs

Signals one WaitHandle and waits on another.

public:
 static bool SignalAndWait(System::Threading::WaitHandle ^ toSignal, System::Threading::WaitHandle ^ toWaitOn);

public static bool SignalAndWait (System.Threading.WaitHandle toSignal, System.Threading.WaitHandle toWaitOn);

static member SignalAndWait : System.Threading.WaitHandle * System.Threading.WaitHandle -> bool

Public Shared Function SignalAndWait (toSignal As WaitHandle, toWaitOn As WaitHandle) As Boolean

Parameters

toSignal

WaitHandle

The WaitHandle to signal.

toWaitOn

WaitHandle

The WaitHandle to wait on.

Returns

Boolean

true if both the signal and the wait complete successfully; if the wait does not complete, the method does not return.

Exceptions

ArgumentNullException

toSignal is null.

-or-

toWaitOn is null.

NotSupportedException

The method was called on a thread in STA state.

InvalidOperationException

toSignal is a semaphore, and it already has a full count.

AbandonedMutexException

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

Examples

The following code example uses the SignalAndWait(WaitHandle, WaitHandle) method overload to allow the main thread to signal a blocked thread and then wait until the thread finishes a task.

The example starts five threads, allows them to block on an EventWaitHandle created with the EventResetMode.AutoReset flag, and then releases one thread each time the user presses the ENTER key. The example then queues another five threads and releases them all using an EventWaitHandle created with the EventResetMode.ManualReset flag.

using namespace System;
using namespace System::Threading;

public ref class Example
{
private:
   // The EventWaitHandle used to demonstrate the difference
   // between AutoReset and ManualReset synchronization events.
   //
   static EventWaitHandle^ ewh;

   // A counter to make sure all threads are started and
   // blocked before any are released. A Long is used to show
   // the use of the 64-bit Interlocked methods.
   //
   static __int64 threadCount = 0;

   // An AutoReset event that allows the main thread to block
   // until an exiting thread has decremented the count.
   //
   static EventWaitHandle^ clearCount =
      gcnew EventWaitHandle( false,EventResetMode::AutoReset );

public:
   [MTAThread]
   static void main()
   {
      // Create an AutoReset EventWaitHandle.
      //
      ewh = gcnew EventWaitHandle( false,EventResetMode::AutoReset );
      
      // Create and start five numbered threads. Use the
      // ParameterizedThreadStart delegate, so the thread
      // number can be passed as an argument to the Start
      // method.
      for ( int i = 0; i <= 4; i++ )
      {
         Thread^ t = gcnew Thread(
            gcnew ParameterizedThreadStart( ThreadProc ) );
         t->Start( i );
      }
      
      // Wait until all the threads have started and blocked.
      // When multiple threads use a 64-bit value on a 32-bit
      // system, you must access the value through the
      // Interlocked class to guarantee thread safety.
      //
      while ( Interlocked::Read( threadCount ) < 5 )
      {
         Thread::Sleep( 500 );
      }

      // Release one thread each time the user presses ENTER,
      // until all threads have been released.
      //
      while ( Interlocked::Read( threadCount ) > 0 )
      {
         Console::WriteLine( L"Press ENTER to release a waiting thread." );
         Console::ReadLine();
         
         // SignalAndWait signals the EventWaitHandle, which
         // releases exactly one thread before resetting,
         // because it was created with AutoReset mode.
         // SignalAndWait then blocks on clearCount, to
         // allow the signaled thread to decrement the count
         // before looping again.
         //
         WaitHandle::SignalAndWait( ewh, clearCount );
      }
      Console::WriteLine();
      
      // Create a ManualReset EventWaitHandle.
      //
      ewh = gcnew EventWaitHandle( false,EventResetMode::ManualReset );
      
      // Create and start five more numbered threads.
      //
      for ( int i = 0; i <= 4; i++ )
      {
         Thread^ t = gcnew Thread(
            gcnew ParameterizedThreadStart( ThreadProc ) );
         t->Start( i );
      }
      
      // Wait until all the threads have started and blocked.
      //
      while ( Interlocked::Read( threadCount ) < 5 )
      {
         Thread::Sleep( 500 );
      }

      // Because the EventWaitHandle was created with
      // ManualReset mode, signaling it releases all the
      // waiting threads.
      //
      Console::WriteLine( L"Press ENTER to release the waiting threads." );
      Console::ReadLine();
      ewh->Set();

   }

   static void ThreadProc( Object^ data )
   {
      int index = static_cast<Int32>(data);

      Console::WriteLine( L"Thread {0} blocks.", data );
      // Increment the count of blocked threads.
      Interlocked::Increment( threadCount );
      
      // Wait on the EventWaitHandle.
      ewh->WaitOne();

      Console::WriteLine( L"Thread {0} exits.", data );
      // Decrement the count of blocked threads.
      Interlocked::Decrement( threadCount );
      
      // After signaling ewh, the main thread blocks on
      // clearCount until the signaled thread has
      // decremented the count. Signal it now.
      //
      clearCount->Set();
   }
};

using System;
using System.Threading;

public class Example
{
    // The EventWaitHandle used to demonstrate the difference
    // between AutoReset and ManualReset synchronization events.
    //
    private static EventWaitHandle ewh;

    // A counter to make sure all threads are started and
    // blocked before any are released. A Long is used to show
    // the use of the 64-bit Interlocked methods.
    //
    private static long threadCount = 0;

    // An AutoReset event that allows the main thread to block
    // until an exiting thread has decremented the count.
    //
    private static EventWaitHandle clearCount = 
        new EventWaitHandle(false, EventResetMode.AutoReset);

    [MTAThread]
    public static void Main()
    {
        // Create an AutoReset EventWaitHandle.
        //
        ewh = new EventWaitHandle(false, EventResetMode.AutoReset);

        // Create and start five numbered threads. Use the
        // ParameterizedThreadStart delegate, so the thread
        // number can be passed as an argument to the Start 
        // method.
        for (int i = 0; i <= 4; i++)
        {
            Thread t = new Thread(
                new ParameterizedThreadStart(ThreadProc)
            );
            t.Start(i);
        }

        // Wait until all the threads have started and blocked.
        // When multiple threads use a 64-bit value on a 32-bit
        // system, you must access the value through the
        // Interlocked class to guarantee thread safety.
        //
        while (Interlocked.Read(ref threadCount) < 5)
        {
            Thread.Sleep(500);
        }

        // Release one thread each time the user presses ENTER,
        // until all threads have been released.
        //
        while (Interlocked.Read(ref threadCount) > 0)
        {
            Console.WriteLine("Press ENTER to release a waiting thread.");
            Console.ReadLine();

            // SignalAndWait signals the EventWaitHandle, which
            // releases exactly one thread before resetting, 
            // because it was created with AutoReset mode. 
            // SignalAndWait then blocks on clearCount, to 
            // allow the signaled thread to decrement the count
            // before looping again.
            //
            WaitHandle.SignalAndWait(ewh, clearCount);
        }
        Console.WriteLine();

        // Create a ManualReset EventWaitHandle.
        //
        ewh = new EventWaitHandle(false, EventResetMode.ManualReset);

        // Create and start five more numbered threads.
        //
        for(int i=0; i<=4; i++)
        {
            Thread t = new Thread(
                new ParameterizedThreadStart(ThreadProc)
            );
            t.Start(i);
        }

        // Wait until all the threads have started and blocked.
        //
        while (Interlocked.Read(ref threadCount) < 5)
        {
            Thread.Sleep(500);
        }

        // Because the EventWaitHandle was created with
        // ManualReset mode, signaling it releases all the
        // waiting threads.
        //
        Console.WriteLine("Press ENTER to release the waiting threads.");
        Console.ReadLine();
        ewh.Set();
    }

    public static void ThreadProc(object data)
    {
        int index = (int) data;

        Console.WriteLine("Thread {0} blocks.", data);
        // Increment the count of blocked threads.
        Interlocked.Increment(ref threadCount);

        // Wait on the EventWaitHandle.
        ewh.WaitOne();

        Console.WriteLine("Thread {0} exits.", data);
        // Decrement the count of blocked threads.
        Interlocked.Decrement(ref threadCount);

        // After signaling ewh, the main thread blocks on
        // clearCount until the signaled thread has 
        // decremented the count. Signal it now.
        //
        clearCount.Set();
    }
}

Imports System.Threading

Public Class Example

    ' The EventWaitHandle used to demonstrate the difference
    ' between AutoReset and ManualReset synchronization events.
    '
    Private Shared ewh As EventWaitHandle

    ' A counter to make sure all threads are started and
    ' blocked before any are released. A Long is used to show
    ' the use of the 64-bit Interlocked methods.
    '
    Private Shared threadCount As Long = 0

    ' An AutoReset event that allows the main thread to block
    ' until an exiting thread has decremented the count.
    '
    Private Shared clearCount As New EventWaitHandle(False, _
        EventResetMode.AutoReset)

    <MTAThread> _
    Public Shared Sub Main()

        ' Create an AutoReset EventWaitHandle.
        '
        ewh = New EventWaitHandle(False, EventResetMode.AutoReset)

        ' Create and start five numbered threads. Use the
        ' ParameterizedThreadStart delegate, so the thread
        ' number can be passed as an argument to the Start 
        ' method.
        For i As Integer = 0 To 4
            Dim t As New Thread(AddressOf ThreadProc)
            t.Start(i)
        Next i

        ' Wait until all the threads have started and blocked.
        ' When multiple threads use a 64-bit value on a 32-bit
        ' system, you must access the value through the
        ' Interlocked class to guarantee thread safety.
        '
        While Interlocked.Read(threadCount) < 5
            Thread.Sleep(500)
        End While

        ' Release one thread each time the user presses ENTER,
        ' until all threads have been released.
        '
        While Interlocked.Read(threadCount) > 0
            Console.WriteLine("Press ENTER to release a waiting thread.")
            Console.ReadLine()

            ' SignalAndWait signals the EventWaitHandle, which
            ' releases exactly one thread before resetting, 
            ' because it was created with AutoReset mode. 
            ' SignalAndWait then blocks on clearCount, to 
            ' allow the signaled thread to decrement the count
            ' before looping again.
            '
            WaitHandle.SignalAndWait(ewh, clearCount)
        End While
        Console.WriteLine()

        ' Create a ManualReset EventWaitHandle.
        '
        ewh = New EventWaitHandle(False, EventResetMode.ManualReset)

        ' Create and start five more numbered threads.
        '
        For i As Integer = 0 To 4
            Dim t As New Thread(AddressOf ThreadProc)
            t.Start(i)
        Next i

        ' Wait until all the threads have started and blocked.
        '
        While Interlocked.Read(threadCount) < 5
            Thread.Sleep(500)
        End While

        ' Because the EventWaitHandle was created with
        ' ManualReset mode, signaling it releases all the
        ' waiting threads.
        '
        Console.WriteLine("Press ENTER to release the waiting threads.")
        Console.ReadLine()
        ewh.Set()
        
    End Sub

    Public Shared Sub ThreadProc(ByVal data As Object)
        Dim index As Integer = CInt(data)

        Console.WriteLine("Thread {0} blocks.", data)
        ' Increment the count of blocked threads.
        Interlocked.Increment(threadCount)

        ' Wait on the EventWaitHandle.
        ewh.WaitOne()

        Console.WriteLine("Thread {0} exits.", data)
        ' Decrement the count of blocked threads.
        Interlocked.Decrement(threadCount)

        ' After signaling ewh, the main thread blocks on
        ' clearCount until the signaled thread has 
        ' decremented the count. Signal it now.
        '
        clearCount.Set()
    End Sub
End Class

Remarks

This operation is not guaranteed to be atomic. After the current thread signals toSignal but before it waits on toWaitOn, a thread that is running on another processor might signal toWaitOn or wait on it.

SignalAndWait(WaitHandle, WaitHandle, Int32, Boolean)

Source:

WaitHandle.cs

Signals one WaitHandle and waits on another, specifying a time-out interval as a 32-bit signed integer and specifying whether to exit the synchronization domain for the context before entering the wait.

public:
 static bool SignalAndWait(System::Threading::WaitHandle ^ toSignal, System::Threading::WaitHandle ^ toWaitOn, int millisecondsTimeout, bool exitContext);

public static bool SignalAndWait (System.Threading.WaitHandle toSignal, System.Threading.WaitHandle toWaitOn, int millisecondsTimeout, bool exitContext);

static member SignalAndWait : System.Threading.WaitHandle * System.Threading.WaitHandle * int * bool -> bool

Public Shared Function SignalAndWait (toSignal As WaitHandle, toWaitOn As WaitHandle, millisecondsTimeout As Integer, exitContext As Boolean) As Boolean

Parameters

toSignal

WaitHandle

The WaitHandle to signal.

toWaitOn

WaitHandle

The WaitHandle to wait on.

millisecondsTimeout

Int32

An integer that represents the interval to wait. If the value is Infinite, that is, -1, the wait is infinite.

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 both the signal and the wait completed successfully, or false if the signal completed but the wait timed out.

Exceptions

ArgumentNullException

toSignal is null.

-or-

toWaitOn is null.

NotSupportedException

The method is called on a thread in STA state.

InvalidOperationException

The WaitHandle cannot be signaled because it would exceed its maximum count.

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.

Remarks

This operation is not guaranteed to be atomic. After the current thread signals toSignal but before it waits on toWaitOn, a thread that is running on another processor might signal toWaitOn or wait on it.

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

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.

SignalAndWait(WaitHandle, WaitHandle, TimeSpan, Boolean)

Source:

WaitHandle.cs

Signals one WaitHandle and waits on another, specifying the time-out interval as a TimeSpan and specifying whether to exit the synchronization domain for the context before entering the wait.

public:
 static bool SignalAndWait(System::Threading::WaitHandle ^ toSignal, System::Threading::WaitHandle ^ toWaitOn, TimeSpan timeout, bool exitContext);

public static bool SignalAndWait (System.Threading.WaitHandle toSignal, System.Threading.WaitHandle toWaitOn, TimeSpan timeout, bool exitContext);

static member SignalAndWait : System.Threading.WaitHandle * System.Threading.WaitHandle * TimeSpan * bool -> bool

Public Shared Function SignalAndWait (toSignal As WaitHandle, toWaitOn As WaitHandle, timeout As TimeSpan, exitContext As Boolean) As Boolean

Parameters

toSignal

WaitHandle

The WaitHandle to signal.

toWaitOn

WaitHandle

The WaitHandle to wait on.

timeout

TimeSpan

A TimeSpan that represents the interval to wait. If the value is -1, the wait is infinite.

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 both the signal and the wait completed successfully, or false if the signal completed but the wait timed out.

Exceptions

ArgumentNullException

toSignal is null.

-or-

toWaitOn is null.

NotSupportedException

The method was called on a thread in STA state.

InvalidOperationException

toSignal is a semaphore, and it already has a full count.

ArgumentOutOfRangeException

timeout evaluates to a negative number of milliseconds other than -1.

-or-

timeout is greater than Int32.MaxValue.

AbandonedMutexException

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

Remarks

This operation is not guaranteed to be atomic. After the current thread signals toSignal but before it waits on toWaitOn, a thread that is running on another processor might signal toWaitOn or wait on it.

The maximum value for timeout is Int32.MaxValue.

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

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.