WaitOrTimerCallback Delegar

Definição

public delegate void WaitOrTimerCallback(System::Object ^ state, bool timedOut);

public delegate void WaitOrTimerCallback(object? state, bool timedOut);

public delegate void WaitOrTimerCallback(object state, bool timedOut);

[System.Runtime.InteropServices.ComVisible(true)]
public delegate void WaitOrTimerCallback(object state, bool timedOut);

type WaitOrTimerCallback = delegate of obj * bool -> unit

[<System.Runtime.InteropServices.ComVisible(true)>]
type WaitOrTimerCallback = delegate of obj * bool -> unit

Public Delegate Sub WaitOrTimerCallback(state As Object, timedOut As Boolean)

Parâmetros

Atributos

ComVisibleAttribute

Exemplos

O exemplo a seguir mostra como usar o WaitOrTimerCallback delegado para representar um método de retorno de chamada executado quando um identificador de espera é sinalizado.

O exemplo também mostra como usar o RegisterWaitForSingleObject método para executar um método de retorno de chamada especificado quando um identificador de espera especificado é sinalizado. Neste exemplo, o método de retorno de chamada é WaitProc e o identificador de espera é um AutoResetEvent.

O exemplo define uma TaskInfo classe para manter as informações passadas para o retorno de chamada quando ela é executada. O exemplo cria um TaskInfo objeto e atribui a ele alguns dados de cadeia de caracteres. O RegisteredWaitHandle que é retornado pelo RegisterWaitForSingleObject método é atribuído ao Handle campo do objeto, de TaskInfo modo que o método de retorno de chamada tenha acesso ao RegisteredWaitHandle.

Além do TaskInfo objeto, a chamada para o RegisterWaitForSingleObject método especifica a AutoResetEvent espera da tarefa, um WaitOrTimerCallback delegado que representa o WaitProc método de retorno de chamada, um intervalo de tempo limite de um segundo e vários retornos de chamada.

Quando o thread principal sinaliza o AutoResetEvent chamando seu Set método, o WaitOrTimerCallback delegado é invocado. O WaitProc método testa RegisteredWaitHandle para determinar se ocorreu um tempo limite. Se o retorno de chamada foi invocado porque o identificador de espera foi sinalizado, o WaitProc método cancela o registro, RegisteredWaitHandleparando outros retornos de chamada. No caso de um tempo limite, a tarefa continua aguardando. O WaitProc método termina imprimindo uma mensagem no console.

using namespace System;
using namespace System::Threading;

// TaskInfo contains data that will be passed to the callback
// method.
public ref class TaskInfo
{
public:
   TaskInfo()
   {
      Handle = nullptr;
      OtherInfo = "default";
   }

   RegisteredWaitHandle^ Handle;
   String^ OtherInfo;
};

ref class Example
{
public:

   // The callback method executes when the registered wait times out,
   // or when the WaitHandle (in this case AutoResetEvent) is signaled.
   // WaitProc unregisters the WaitHandle the first time the event is 
   // signaled.
   static void WaitProc( Object^ state, bool timedOut )
   {
      
      // The state Object must be cast to the correct type, because the
      // signature of the WaitOrTimerCallback delegate specifies type
      // Object.
      TaskInfo^ ti = static_cast<TaskInfo^>(state);
      String^ cause = "TIMED OUT";
      if (  !timedOut )
      {
         cause = "SIGNALED";
         
         // If the callback method executes because the WaitHandle is
         // signaled, stop future execution of the callback method
         // by unregistering the WaitHandle.
         if ( ti->Handle != nullptr )
                  ti->Handle->Unregister( nullptr );
      }

      Console::WriteLine( "WaitProc( {0}) executes on thread {1}; cause = {2}.", ti->OtherInfo, Thread::CurrentThread->GetHashCode(), cause );
   }

};

int main()
{
   
   // The main thread uses AutoResetEvent to signal the
   // registered wait handle, which executes the callback
   // method.
   AutoResetEvent^ ev = gcnew AutoResetEvent( false );
   TaskInfo^ ti = gcnew TaskInfo;
   ti->OtherInfo = "First task";
   
   // The TaskInfo for the task includes the registered wait
   // handle returned by RegisterWaitForSingleObject.  This
   // allows the wait to be terminated when the object has
   // been signaled once (see WaitProc).
   ti->Handle = ThreadPool::RegisterWaitForSingleObject( ev, gcnew WaitOrTimerCallback( Example::WaitProc ), ti, 1000, false );
   
   // The main thread waits three seconds, to demonstrate the
   // time-outs on the queued thread, and then signals.
   Thread::Sleep( 3100 );
   Console::WriteLine( "Main thread signals." );
   ev->Set();
   
   // The main thread sleeps, which should give the callback
   // method time to execute.  If you comment out this line, the
   // program usually ends before the ThreadPool thread can execute.
   Thread::Sleep( 1000 );
   
   // If you start a thread yourself, you can wait for it to end
   // by calling Thread::Join.  This option is not available with 
   // thread pool threads.
   return 0;
}

using System;
using System.Threading;

// TaskInfo contains data that will be passed to the callback
// method.
public class TaskInfo {
    public RegisteredWaitHandle Handle = null;
    public string OtherInfo = "default";
}

public class Example {
    public static void Main(string[] args) {
        // The main thread uses AutoResetEvent to signal the
        // registered wait handle, which executes the callback
        // method.
        AutoResetEvent ev = new AutoResetEvent(false);

        TaskInfo ti = new TaskInfo();
        ti.OtherInfo = "First task";
        // The TaskInfo for the task includes the registered wait
        // handle returned by RegisterWaitForSingleObject.  This
        // allows the wait to be terminated when the object has
        // been signaled once (see WaitProc).
        ti.Handle = ThreadPool.RegisterWaitForSingleObject(
            ev,
            new WaitOrTimerCallback(WaitProc),
            ti,
            1000,
            false
        );

        // The main thread waits three seconds, to demonstrate the
        // time-outs on the queued thread, and then signals.
        Thread.Sleep(3100);
        Console.WriteLine("Main thread signals.");
        ev.Set();

        // The main thread sleeps, which should give the callback
        // method time to execute.  If you comment out this line, the
        // program usually ends before the ThreadPool thread can execute.
        Thread.Sleep(1000);
        // If you start a thread yourself, you can wait for it to end
        // by calling Thread.Join.  This option is not available with 
        // thread pool threads.
    }
   
    // The callback method executes when the registered wait times out,
    // or when the WaitHandle (in this case AutoResetEvent) is signaled.
    // WaitProc unregisters the WaitHandle the first time the event is 
    // signaled.
    public static void WaitProc(object state, bool timedOut) {
        // The state object must be cast to the correct type, because the
        // signature of the WaitOrTimerCallback delegate specifies type
        // Object.
        TaskInfo ti = (TaskInfo) state;

        string cause = "TIMED OUT";
        if (!timedOut) {
            cause = "SIGNALED";
            // If the callback method executes because the WaitHandle is
            // signaled, stop future execution of the callback method
            // by unregistering the WaitHandle.
            if (ti.Handle != null)
                ti.Handle.Unregister(null);
        } 

        Console.WriteLine("WaitProc( {0} ) executes on thread {1}; cause = {2}.",
            ti.OtherInfo, 
            Thread.CurrentThread.GetHashCode().ToString(), 
            cause
        );
    }
}

Imports System.Threading

' TaskInfo contains data that will be passed to the callback
' method.
Public Class TaskInfo
    public Handle As RegisteredWaitHandle = Nothing
    public OtherInfo As String = "default"
End Class

Public Class Example

    <MTAThread> _
    Public Shared Sub Main()
        ' The main thread uses AutoResetEvent to signal the
        ' registered wait handle, which executes the callback
        ' method.
        Dim ev As New AutoResetEvent(false)

        Dim ti As New TaskInfo()
        ti.OtherInfo = "First task"
        ' The TaskInfo for the task includes the registered wait
        ' handle returned by RegisterWaitForSingleObject.  This
        ' allows the wait to be terminated when the object has
        ' been signaled once (see WaitProc).
        ti.Handle = ThreadPool.RegisterWaitForSingleObject( _
            ev, _
            New WaitOrTimerCallback(AddressOf WaitProc), _
            ti, _
            1000, _
            false _
        )

        ' The main thread waits about three seconds, to demonstrate 
        ' the time-outs on the queued task, and then signals.
        Thread.Sleep(3100)
        Console.WriteLine("Main thread signals.")
        ev.Set()

        ' The main thread sleeps, which should give the callback
        ' method time to execute.  If you comment out this line, the
        ' program usually ends before the ThreadPool thread can execute.
        Thread.Sleep(1000)
        ' If you start a thread yourself, you can wait for it to end
        ' by calling Thread.Join.  This option is not available with 
        ' thread pool threads.
    End Sub
   
    ' The callback method executes when the registered wait times out,
    ' or when the WaitHandle (in this case AutoResetEvent) is signaled.
    ' WaitProc unregisters the WaitHandle the first time the event is 
    ' signaled.
    Public Shared Sub WaitProc(state As Object, timedOut As Boolean)
        ' The state object must be cast to the correct type, because the
        ' signature of the WaitOrTimerCallback delegate specifies type
        ' Object.
        Dim ti As TaskInfo = CType(state, TaskInfo)

        Dim cause As String = "TIMED OUT"
        If Not timedOut Then
            cause = "SIGNALED"
            ' If the callback method executes because the WaitHandle is
            ' signaled, stop future execution of the callback method
            ' by unregistering the WaitHandle.
            If Not ti.Handle Is Nothing Then
                ti.Handle.Unregister(Nothing)
            End If
        End If 

        Console.WriteLine("WaitProc( {0} ) executes on thread {1}; cause = {2}.", _
            ti.OtherInfo, _
            Thread.CurrentThread.GetHashCode().ToString(), _
            cause _
        )
    End Sub
End Class

Comentários

WaitOrTimerCallback representa um método de retorno de chamada que você deseja executar quando um identificador de espera registrado atingir o tempo limite ou for sinalizado. Crie o delegado passando o método de retorno de chamada para o WaitOrTimerCallback construtor. Seu método deve ter a assinatura mostrada aqui.

Crie o identificador de espera registrado passando o WaitOrTimerCallback delegado e a WaitHandle para ThreadPool.RegisterWaitForSingleObject. Seu método de retorno de chamada é executado sempre que o WaitHandle tempo limite ou é sinalizado.

Se você quiser passar informações para o método de retorno de chamada, crie um objeto que contenha as informações necessárias e passe-as para RegisterWaitForSingleObject quando você criar o identificador de espera registrado. Cada vez que o método de retorno de chamada é executado, o state parâmetro contém esse objeto.

Para obter mais informações sobre como usar métodos de retorno de chamada para sincronizar threads do pool de threads, consulte o pool de threads gerenciado.

Métodos de Extensão

Aplica-se a

Confira também

• Threads e threading
• O pool de threads gerenciados