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Appel de méthodes synchrones de façon asynchrone

.NET Framework permet d'appeler n'importe quelle méthode de façon asynchrone. Pour ce faire, définissez un délégué possédant la même signature que la méthode à appeler ; le Common Language Runtime définit automatiquement les méthodes BeginInvoke et EndInvoke pour ce délégué avec les signatures appropriées.

RemarqueRemarque

Les appels de délégués asynchrones, notamment les méthodes BeginInvoke et EndInvoke, ne sont pas prises en charge dans le .NET Compact Framework.

La méthode BeginInvoke lance l'appel asynchrone. Elle possède les mêmes paramètres que la méthode à exécuter de façon asynchrone, plus deux paramètres facultatifs. Le premier paramètre est un délégué AsyncCallback qui fait référence à une méthode à appeler lorsque l'appel asynchrone se termine. Le deuxième paramètre est un objet défini par l'utilisateur qui passe des informations vers la méthode de rappel. BeginInvoke est retourné immédiatement et n'attend pas la fin de l'appel asynchrone. BeginInvoke retourne un IAsyncResult, qui peut être utilisé pour surveiller la progression de l'appel asynchrone.

La méthode EndInvoke récupère les résultats de l'appel asynchrone. Il peut être appelé à tout moment après BeginInvoke. Si l'appel asynchrone n'est pas terminé, EndInvoke stoppe le thread appelant jusqu'à la fin de l'appel. Les paramètres de EndInvoke comprennent les paramètres out et ref (<Out> ByRef et ByRef dans Visual Basic) de la méthode à exécuter de façon asynchrone, en plus du IAsyncResult retourné par BeginInvoke.

RemarqueRemarque

La fonctionnalité IntelliSense de Visual Studio 2005 affiche les paramètres des méthodes BeginInvoke et EndInvoke.Si vous n'utilisez ni Visual Studio ni un outil similaire, ou si vous utilisez C# avec Visual Studio 2005, consultez Vue d'ensemble de la programmation asynchrone pour une description des paramètres définis pour ces méthodes.

Les exemples de code de cette rubrique illustrent quatre utilisations classiques des méthodes BeginInvoke et EndInvoke pour effectuer des appels asynchrones. Après un appel à BeginInvoke, vous pouvez effectuer les opérations suivantes :

  • travailler un moment, puis appeler EndInvoke pour que la méthode se bloque jusqu'à la fin de l'appel ;

  • obtenir un WaitHandle à l'aide de la propriété IAsyncResult.AsyncWaitHandle, utiliser sa méthode WaitOne pour bloquer l'exécution jusqu'à ce que le WaitHandle soit signalé, puis appeler EndInvoke ;

  • interroger le IAsyncResult retourné par BeginInvoke pour savoir à quel moment l'appel s'est terminé, puis appeler EndInvoke ;

  • passer un délégué d'une méthode de rappel à BeginInvoke. La méthode est exécutée sur un thread ThreadPool lorsque l'appel asynchrone se termine. La méthode de rappel appelle EndInvoke.

Remarque importanteImportant

Quelle que soit la technique utilisée, appelez toujours EndInvoke pour terminer un appel asynchrone.

Définition de la méthode de test et du délégué asynchrone

Les exemples de code suivants illustrent différentes façons d'appeler la même méthode longue, TestMethod, de façon asynchrone. La méthode TestMethod affiche un message sur la console pour indiquer que son traitement a commencé, se met en veille pendant quelques secondes, puis se termine. TestMethod a un paramètre de out pour illustrer la façon dont ces paramètres sont ajoutés aux signatures de BeginInvoke et EndInvoke. Vous pouvez gérer les paramètres ref de façon similaire.

L'exemple de code suivant illustre la définition de TestMethod et le délégué nommé AsyncMethodCaller qui peut être utilisé pour appeler TestMethod de façon asynchrone. Pour compiler les exemples de code, vous devez inclure les définitions pour TestMethod et pour le délégué AsyncMethodCaller.

Imports System
Imports System.Threading
Imports System.Runtime.InteropServices 

Namespace Examples.AdvancedProgramming.AsynchronousOperations
    Public Class AsyncDemo 
        ' The method to be executed asynchronously.
        Public Function TestMethod(ByVal callDuration As Integer, _
                <Out> ByRef threadId As Integer) As String
            Console.WriteLine("Test method begins.")
            Thread.Sleep(callDuration)
            threadId = Thread.CurrentThread.ManagedThreadId()
            return String.Format("My call time was {0}.", callDuration.ToString())
        End Function
    End Class

    ' The delegate must have the same signature as the method
    ' it will call asynchronously.
    Public Delegate Function AsyncMethodCaller(ByVal callDuration As Integer, _
        <Out> ByRef threadId As Integer) As String
End Namespace
using System;
using System.Threading; 

namespace Examples.AdvancedProgramming.AsynchronousOperations
{
    public class AsyncDemo 
    {
        // The method to be executed asynchronously.
        public string TestMethod(int callDuration, out int threadId) 
        {
            Console.WriteLine("Test method begins.");
            Thread.Sleep(callDuration);
            threadId = Thread.CurrentThread.ManagedThreadId;
            return String.Format("My call time was {0}.", callDuration.ToString());
        }
    }
    // The delegate must have the same signature as the method
    // it will call asynchronously.
    public delegate string AsyncMethodCaller(int callDuration, out int threadId);
}
using namespace System;
using namespace System::Threading;
using namespace System::Runtime::InteropServices; 

namespace Examples {
namespace AdvancedProgramming {
namespace AsynchronousOperations
{
    public ref class AsyncDemo 
    {
    public:
        // The method to be executed asynchronously.
        String^ TestMethod(int callDuration, [OutAttribute] int% threadId) 
        {
            Console::WriteLine("Test method begins.");
            Thread::Sleep(callDuration);
            threadId = Thread::CurrentThread->ManagedThreadId;
            return String::Format("My call time was {0}.", callDuration);
        }
    };

    // The delegate must have the same signature as the method
    // it will call asynchronously.
    public delegate String^ AsyncMethodCaller(int callDuration, [OutAttribute] int% threadId);
}}}

Attente d'un appel asynchrone avec EndInvoke

La façon la plus simple d'exécuter une méthode de façon asynchrone est de commencer à exécuter la méthode en appelant la méthode BeginInvoke du délégué, de travailler un peu sur le thread principal, puis d'appeler la méthode EndInvoke du délégué. EndInvoke peut bloquer le thread appelant, car il n'est pas retourné tant que l'appel asynchrone n'est pas terminé. Cette technique est utile avec les opérations de fichier ou de réseau.

Remarque importanteImportant

Étant donné que EndInvoke peut se bloquer, ne l'appelez jamais à partir de threads qui servent à l'interface utilisateur.

Imports System
Imports System.Threading
Imports System.Runtime.InteropServices 

Namespace Examples.AdvancedProgramming.AsynchronousOperations
    Public Class AsyncMain 
        Shared Sub Main() 
            ' The asynchronous method puts the thread id here.
            Dim threadId As Integer

            ' Create an instance of the test class.
            Dim ad As New AsyncDemo()

            ' Create the delegate.
            Dim caller As New AsyncMethodCaller(AddressOf ad.TestMethod)

            ' Initiate the asynchronous call.
            Dim result As IAsyncResult = caller.BeginInvoke(3000, _
                threadId, Nothing, Nothing)

            Thread.Sleep(0)
            Console.WriteLine("Main thread {0} does some work.", _
                 Thread.CurrentThread.ManagedThreadId)

            ' Call EndInvoke to Wait for the asynchronous call to complete,
            ' and to retrieve the results.
            Dim returnValue As String = caller.EndInvoke(threadId, result)

            Console.WriteLine("The call executed on thread {0}, with return value ""{1}"".", _
                threadId, returnValue)
        End Sub
    End Class

End Namespace

'This example produces output similar to the following:
'
'Main thread 1 does some work.
'Test method begins.
'The call executed on thread 3, with return value "My call time was 3000.".
using System;
using System.Threading;

namespace Examples.AdvancedProgramming.AsynchronousOperations
{
    public class AsyncMain 
    {
        public static void Main() 
        {
            // The asynchronous method puts the thread id here.
            int threadId;

            // Create an instance of the test class.
            AsyncDemo ad = new AsyncDemo();

            // Create the delegate.
            AsyncMethodCaller caller = new AsyncMethodCaller(ad.TestMethod);

            // Initiate the asychronous call.
            IAsyncResult result = caller.BeginInvoke(3000, 
                out threadId, null, null);

            Thread.Sleep(0);
            Console.WriteLine("Main thread {0} does some work.",
                Thread.CurrentThread.ManagedThreadId);

            // Call EndInvoke to wait for the asynchronous call to complete,
            // and to retrieve the results.
            string returnValue = caller.EndInvoke(out threadId, result);

            Console.WriteLine("The call executed on thread {0}, with return value \"{1}\".",
                threadId, returnValue);
        }
    }
}

/* This example produces output similar to the following:

Main thread 1 does some work.
Test method begins.
The call executed on thread 3, with return value "My call time was 3000.".
 */
#using <TestMethod.dll>

using namespace System;
using namespace System::Threading;
using namespace Examples::AdvancedProgramming::AsynchronousOperations;

void main() 
{
    // The asynchronous method puts the thread id here.
    int threadId = 2546;

    // Create an instance of the test class.
    AsyncDemo^ ad = gcnew AsyncDemo();

    // Create the delegate.
    AsyncMethodCaller^ caller = gcnew AsyncMethodCaller(ad, &AsyncDemo::TestMethod);

    // Initiate the asychronous call.
    IAsyncResult^ result = caller->BeginInvoke(3000, 
        threadId, nullptr, nullptr);

    Thread::Sleep(1);
    Console::WriteLine("Main thread {0} does some work.",
        Thread::CurrentThread->ManagedThreadId);

    // Call EndInvoke to wait for the asynchronous call to complete,
    // and to retrieve the results.
    String^ returnValue = caller->EndInvoke(threadId, result);

    Console::WriteLine("The call executed on thread {0}, with return value \"{1}\".",
        threadId, returnValue);
}

/* This example produces output similar to the following:

Main thread 1 does some work.
Test method begins.
The call executed on thread 3, with return value "My call time was 3000.".
 */

Attente d'un appel asynchrone avec WaitHandle

Vous pouvez obtenir un WaitHandle à l'aide de la propriété AsyncWaitHandle du IAsyncResult retourné par BeginInvoke. Le WaitHandle est signalé lorsque l'appel asynchrone se termine et vous pouvez l'attendre en appelant la méthode WaitOne.

Si vous utilisez un WaitHandle, vous pouvez effectuer un traitement supplémentaire avant ou après la fin de l'appel asynchrone, mais avant d'appeler EndInvoke pour récupérer les résultats.

RemarqueRemarque

Le handle d'attente ne se ferme pas automatiquement lorsque vous appelez EndInvoke.Si vous diffusez toutes les références au handle d'attente, les ressources système sont libérées lorsque le garbage collection libère le handle d'attente.Pour libérer les ressources système, dès que vous avez fini d'utiliser le handle d'attente, supprimez-le en appelant la méthode WaitHandle.Close.Le garbage collection est plus efficace lorsque les objets pouvant être supprimés sont clairement supprimés.

Imports System
Imports System.Threading
Imports System.Runtime.InteropServices 

Namespace Examples.AdvancedProgramming.AsynchronousOperations

    Public Class AsyncMain 
        Shared Sub Main() 
            ' The asynchronous method puts the thread id here.
            Dim threadId As Integer

            ' Create an instance of the test class.
            Dim ad As New AsyncDemo()

            ' Create the delegate.
            Dim caller As New AsyncMethodCaller(AddressOf ad.TestMethod)

            ' Initiate the asynchronous call.
            Dim result As IAsyncResult = caller.BeginInvoke(3000, _
                threadId, Nothing, Nothing)

            Thread.Sleep(0)
            Console.WriteLine("Main thread {0} does some work.", _
                Thread.CurrentThread.ManagedThreadId)
            ' Perform additional processing here and then
            ' wait for the WaitHandle to be signaled.
            result.AsyncWaitHandle.WaitOne()

            ' Call EndInvoke to retrieve the results.
            Dim returnValue As String = caller.EndInvoke(threadId, result)

            ' Close the wait handle.
            result.AsyncWaitHandle.Close()

            Console.WriteLine("The call executed on thread {0}, with return value ""{1}"".", _
                threadId, returnValue)
        End Sub
    End Class
End Namespace

'This example produces output similar to the following:
'
'Main thread 1 does some work.
'Test method begins.
'The call executed on thread 3, with return value "My call time was 3000.".
using System;
using System.Threading;

namespace Examples.AdvancedProgramming.AsynchronousOperations
{
    public class AsyncMain 
    {
        static void Main() 
        {
            // The asynchronous method puts the thread id here.
            int threadId;

            // Create an instance of the test class.
            AsyncDemo ad = new AsyncDemo();

            // Create the delegate.
            AsyncMethodCaller caller = new AsyncMethodCaller(ad.TestMethod);

            // Initiate the asychronous call.
            IAsyncResult result = caller.BeginInvoke(3000, 
                out threadId, null, null);

            Thread.Sleep(0);
            Console.WriteLine("Main thread {0} does some work.",
                Thread.CurrentThread.ManagedThreadId);

            // Wait for the WaitHandle to become signaled.
            result.AsyncWaitHandle.WaitOne();

            // Perform additional processing here.
            // Call EndInvoke to retrieve the results.
            string returnValue = caller.EndInvoke(out threadId, result);

            // Close the wait handle.
            result.AsyncWaitHandle.Close();

            Console.WriteLine("The call executed on thread {0}, with return value \"{1}\".",
                threadId, returnValue);
        }
    }
}

/* This example produces output similar to the following:

Main thread 1 does some work.
Test method begins.
The call executed on thread 3, with return value "My call time was 3000.".
 */
#using <TestMethod.dll>

using namespace System;
using namespace System::Threading;
using namespace Examples::AdvancedProgramming::AsynchronousOperations;

void main() 
{
    // The asynchronous method puts the thread id here.
    int threadId;

    // Create an instance of the test class.
    AsyncDemo^ ad = gcnew AsyncDemo();

    // Create the delegate.
    AsyncMethodCaller^ caller = gcnew AsyncMethodCaller(ad, &AsyncDemo::TestMethod);

    // Initiate the asychronous call.
    IAsyncResult^ result = caller->BeginInvoke(3000, 
        threadId, nullptr, nullptr);

    Thread::Sleep(0);
    Console::WriteLine("Main thread {0} does some work.",
        Thread::CurrentThread->ManagedThreadId);

    // Wait for the WaitHandle to become signaled.
    result->AsyncWaitHandle->WaitOne();

    // Perform additional processing here.
    // Call EndInvoke to retrieve the results.
    String^ returnValue = caller->EndInvoke(threadId, result);

    // Close the wait handle.
    result->AsyncWaitHandle->Close();

    Console::WriteLine("The call executed on thread {0}, with return value \"{1}\".",
        threadId, returnValue);
}

/* This example produces output similar to the following:

Main thread 1 does some work.
Test method begins.
The call executed on thread 3, with return value "My call time was 3000.".
 */

Interrogation de la fin d'un appel asynchrone

Vous pouvez utiliser la propriété IsCompleted du IAsyncResult retourné par BeginInvoke pour savoir à quel moment l'appel asynchrone se termine. Vous pouvez effectuer cette opération lorsque vous établissez l'appel asynchrone à partir d'un thread desservant l'interface utilisateur. L'interrogation permet alors au thread appelant de continuer à s'exécuter pendant que l'appel asynchrone s'exécute sur un thread ThreadPool.

Imports System
Imports System.Threading
Imports System.Runtime.InteropServices 

Namespace Examples.AdvancedProgramming.AsynchronousOperations

    Public Class AsyncMain 
        Shared Sub Main() 
            ' The asynchronous method puts the thread id here.
            Dim threadId As Integer

            ' Create an instance of the test class.
            Dim ad As New AsyncDemo()

            ' Create the delegate.
            Dim caller As New AsyncMethodCaller(AddressOf ad.TestMethod)

            ' Initiate the asynchronous call.
            Dim result As IAsyncResult = caller.BeginInvoke(3000, _
                threadId, Nothing, Nothing)

            ' Poll while simulating work.
            While result.IsCompleted = False
                Thread.Sleep(250)
                Console.Write(".")
            End While

            ' Call EndInvoke to retrieve the results.
            Dim returnValue As String = caller.EndInvoke(threadId, result)

            Console.WriteLine(vbCrLf & _
                "The call executed on thread {0}, with return value ""{1}"".", _
                threadId, returnValue)
        End Sub
    End Class
End Namespace

' This example produces output similar to the following:
'
'Test method begins.
'.............
'The call executed on thread 3, with return value "My call time was 3000.".
using System;
using System.Threading;

namespace Examples.AdvancedProgramming.AsynchronousOperations
{
    public class AsyncMain 
    {
        static void Main() {
            // The asynchronous method puts the thread id here.
            int threadId;

            // Create an instance of the test class.
            AsyncDemo ad = new AsyncDemo();

            // Create the delegate.
            AsyncMethodCaller caller = new AsyncMethodCaller(ad.TestMethod);

            // Initiate the asychronous call.
            IAsyncResult result = caller.BeginInvoke(3000, 
                out threadId, null, null);

            // Poll while simulating work.
            while(result.IsCompleted == false) {
                Thread.Sleep(250);
                Console.Write(".");
            }

            // Call EndInvoke to retrieve the results.
            string returnValue = caller.EndInvoke(out threadId, result);

            Console.WriteLine("\nThe call executed on thread {0}, with return value \"{1}\".",
                threadId, returnValue);
        }
    }
}

/* This example produces output similar to the following:

Test method begins.
.............
The call executed on thread 3, with return value "My call time was 3000.".
 */
#using <TestMethod.dll>

using namespace System;
using namespace System::Threading;
using namespace Examples::AdvancedProgramming::AsynchronousOperations;

void main() 
{
    // The asynchronous method puts the thread id here.
    int threadId;

    // Create an instance of the test class.
    AsyncDemo^ ad = gcnew AsyncDemo();

    // Create the delegate.
    AsyncMethodCaller^ caller = gcnew AsyncMethodCaller(ad, &AsyncDemo::TestMethod);

    // Initiate the asychronous call.
    IAsyncResult^ result = caller->BeginInvoke(3000, 
        threadId, nullptr, nullptr);

    // Poll while simulating work.
    while(result->IsCompleted == false)
    {
        Thread::Sleep(250);
        Console::Write(".");
    }

    // Call EndInvoke to retrieve the results.
    String^ returnValue = caller->EndInvoke(threadId, result);

    Console::WriteLine("\nThe call executed on thread {0}, with return value \"{1}\".",
        threadId, returnValue);
}

/* This example produces output similar to the following:

Test method begins.
.............
The call executed on thread 3, with return value "My call time was 3000.".
 */

Exécution d'une méthode de rappel à la fin d'un appel asynchrone

Si le thread qui lance l'appel asynchrone ne doit pas forcément traiter les résultats, vous pouvez exécuter une méthode de rappel lorsque l'appel se termine. La méthode de rappel est exécutée sur un thread ThreadPool.

Pour utiliser une méthode de rappel, vous devez passer un délégué AsyncCallback, qui représente la méthode de rappel, à BeginInvoke. Vous pouvez également passer un objet qui contient des informations qui seront exploitées par la méthode de rappel. Dans la méthode de rappel, vous pouvez effectuer un cast de IAsyncResult, qui est le seul paramètre de la méthode de rappel, en un objet AsyncResult. Vous pouvez ensuite utiliser la propriété AsyncResult.AsyncDelegate pour obtenir le délégué utilisé pour lancer l'appel afin que vous puissiez appeler EndInvoke.

Remarques sur l'exemple :

  • Le paramètre threadId de TestMethod est un paramètre out (< Out > ByRef dans Visual Basic), donc sa valeur d'entrée n'est jamais utilisée par TestMethod. Une variable factice est passée à l'appel BeginInvoke. Si le paramètre threadId était un paramètre ref (ByRef dans Visual Basic), la variable devrait être un champ de niveau classe afin d'être passée à BeginInvoke et EndInvoke.

  • Les informations d'état passées à BeginInvoke sont des chaînes de format utilisées par la méthode de rappel pour mettre en forme un message de sortie. Puisqu'elles sont passées en tant que type Object, les informations d'état doivent être castées en leurs propres types avant d'être utilisées.

  • Le rappel est effectué sur un thread ThreadPool. Les threads ThreadPool sont des threads d'arrière-plan qui arrêtent l'application si les threads principaux se terminent ; le thread principal de l'exemple doit donc se mettre en veille assez longtemps pour que le rappel se termine.

Imports System
Imports System.Threading
Imports System.Runtime.Remoting.Messaging

Namespace Examples.AdvancedProgramming.AsynchronousOperations

    Public Class AsyncMain 

        Shared Sub Main() 

            ' Create an instance of the test class.
            Dim ad As New AsyncDemo()

            ' Create the delegate.
            Dim caller As New AsyncMethodCaller(AddressOf ad.TestMethod)

            ' The threadId parameter of TestMethod is an <Out> parameter, so
            ' its input value is never used by TestMethod. Therefore, a dummy
            ' variable can be passed to the BeginInvoke call. If the threadId
            ' parameter were a ByRef parameter, it would have to be a class-
            ' level field so that it could be passed to both BeginInvoke and 
            ' EndInvoke.
            Dim dummy As Integer = 0

            ' Initiate the asynchronous call, passing three seconds (3000 ms)
            ' for the callDuration parameter of TestMethod; a dummy variable 
            ' for the <Out> parameter (threadId); the callback delegate; and
            ' state information that can be retrieved by the callback method.
            ' In this case, the state information is a string that can be used
            ' to format a console message.
            Dim result As IAsyncResult = caller.BeginInvoke(3000, _
                dummy, _
                AddressOf CallbackMethod, _
                "The call executed on thread {0}, with return value ""{1}"".")

            Console.WriteLine("The main thread {0} continues to execute...", _
                Thread.CurrentThread.ManagedThreadId)

            ' The callback is made on a ThreadPool thread. ThreadPool threads
            ' are background threads, which do not keep the application running
            ' if the main thread ends. Comment out the next line to demonstrate
            ' this.
            Thread.Sleep(4000)

            Console.WriteLine("The main thread ends.")
        End Sub

        ' The callback method must have the same signature as the
        ' AsyncCallback delegate.
        Shared Sub CallbackMethod(ByVal ar As IAsyncResult)
            ' Retrieve the delegate.
            Dim result As AsyncResult = CType(ar, AsyncResult)
            Dim caller As AsyncMethodCaller = CType(result.AsyncDelegate, AsyncMethodCaller)

            ' Retrieve the format string that was passed as state 
            ' information.
            Dim formatString As String = CType(ar.AsyncState, String)

            ' Define a variable to receive the value of the <Out> parameter.
            ' If the parameter were ByRef rather than <Out> then it would have to
            ' be a class-level field so it could also be passed to BeginInvoke.
            Dim threadId As Integer = 0

            ' Call EndInvoke to retrieve the results.
            Dim returnValue As String = caller.EndInvoke(threadId, ar)

            ' Use the format string to format the output message.
            Console.WriteLine(formatString, threadId, returnValue)
        End Sub
    End Class
End Namespace

' This example produces output similar to the following:
'
'The main thread 1 continues to execute...
'Test method begins.
'The call executed on thread 3, with return value "My call time was 3000.".
'The main thread ends.
using System;
using System.Threading;
using System.Runtime.Remoting.Messaging;

namespace Examples.AdvancedProgramming.AsynchronousOperations
{
    public class AsyncMain 
    {
        static void Main() 
        {
            // Create an instance of the test class.
            AsyncDemo ad = new AsyncDemo();

            // Create the delegate.
            AsyncMethodCaller caller = new AsyncMethodCaller(ad.TestMethod);

            // The threadId parameter of TestMethod is an out parameter, so
            // its input value is never used by TestMethod. Therefore, a dummy
            // variable can be passed to the BeginInvoke call. If the threadId
            // parameter were a ref parameter, it would have to be a class-
            // level field so that it could be passed to both BeginInvoke and 
            // EndInvoke.
            int dummy = 0;

            // Initiate the asynchronous call, passing three seconds (3000 ms)
            // for the callDuration parameter of TestMethod; a dummy variable 
            // for the out parameter (threadId); the callback delegate; and
            // state information that can be retrieved by the callback method.
            // In this case, the state information is a string that can be used
            // to format a console message.
            IAsyncResult result = caller.BeginInvoke(3000,
                out dummy, 
                new AsyncCallback(CallbackMethod),
                "The call executed on thread {0}, with return value \"{1}\".");

            Console.WriteLine("The main thread {0} continues to execute...", 
                Thread.CurrentThread.ManagedThreadId);

            // The callback is made on a ThreadPool thread. ThreadPool threads
            // are background threads, which do not keep the application running
            // if the main thread ends. Comment out the next line to demonstrate
            // this.
            Thread.Sleep(4000);

            Console.WriteLine("The main thread ends.");
        }

        // The callback method must have the same signature as the
        // AsyncCallback delegate.
        static void CallbackMethod(IAsyncResult ar) 
        {
            // Retrieve the delegate.
            AsyncResult result = (AsyncResult) ar;
            AsyncMethodCaller caller = (AsyncMethodCaller) result.AsyncDelegate;

            // Retrieve the format string that was passed as state 
            // information.
            string formatString = (string) ar.AsyncState;

            // Define a variable to receive the value of the out parameter.
            // If the parameter were ref rather than out then it would have to
            // be a class-level field so it could also be passed to BeginInvoke.
            int threadId = 0;

            // Call EndInvoke to retrieve the results.
            string returnValue = caller.EndInvoke(out threadId, ar);

            // Use the format string to format the output message.
            Console.WriteLine(formatString, threadId, returnValue);
        }
    }
}

/* This example produces output similar to the following:

The main thread 1 continues to execute...
Test method begins.
The call executed on thread 3, with return value "My call time was 3000.".
The main thread ends.
 */
#using <TestMethod.dll>

using namespace System;
using namespace System::Threading;
using namespace System::Runtime::Remoting::Messaging;
using namespace Examples::AdvancedProgramming::AsynchronousOperations;

// The callback method must have the same signature as the
// AsyncCallback delegate.
void CallbackMethod(IAsyncResult^ ar) 
{
    // Retrieve the delegate.
    AsyncResult^ result = (AsyncResult^) ar;
    AsyncMethodCaller^ caller = (AsyncMethodCaller^) result->AsyncDelegate;

    // Retrieve the format string that was passed as state 
    // information.
    String^ formatString = (String^) ar->AsyncState;

    // Define a variable to receive the value of the out parameter.
    // If the parameter were ref rather than out then it would have to
    // be a class-level field so it could also be passed to BeginInvoke.
    int threadId = 0;

    // Call EndInvoke to retrieve the results.
    String^ returnValue = caller->EndInvoke(threadId, ar);

    // Use the format string to format the output message.
    Console::WriteLine(formatString, threadId, returnValue);
};

void main() 
{
    // Create an instance of the test class.
    AsyncDemo^ ad = gcnew AsyncDemo();

    // Create the delegate.
    AsyncMethodCaller^ caller = gcnew AsyncMethodCaller(ad, &AsyncDemo::TestMethod);

    // The threadId parameter of TestMethod is an out parameter, so
    // its input value is never used by TestMethod. Therefore, a dummy
    // variable can be passed to the BeginInvoke call. If the threadId
    // parameter were a ref parameter, it would have to be a class-
    // level field so that it could be passed to both BeginInvoke and 
    // EndInvoke.
    int dummy = 0;

    // Initiate the asynchronous call, passing three seconds (3000 ms)
    // for the callDuration parameter of TestMethod; a dummy variable 
    // for the out parameter (threadId); the callback delegate; and
    // state information that can be retrieved by the callback method.
    // In this case, the state information is a string that can be used
    // to format a console message.
    IAsyncResult^ result = caller->BeginInvoke(3000,
        dummy, 
        gcnew AsyncCallback(&CallbackMethod),
        "The call executed on thread {0}, with return value \"{1}\".");

    Console::WriteLine("The main thread {0} continues to execute...", 
        Thread::CurrentThread->ManagedThreadId);

    // The callback is made on a ThreadPool thread. ThreadPool threads
    // are background threads, which do not keep the application running
    // if the main thread ends. Comment out the next line to demonstrate
    // this.
    Thread::Sleep(4000);
    Console::WriteLine("The main thread ends.");
}

/* This example produces output similar to the following:

The main thread 1 continues to execute...
Test method begins.
The call executed on thread 3, with return value "My call time was 3000.".
The main thread ends.
 */

Voir aussi

Référence

Delegate

Autres ressources

Modèles de conception pour la programmation asynchrone