IAsyncResult.AsyncWaitHandle Propriedade

Definição

Obtém um WaitHandle que é usado para aguardar a conclusão de uma operação assíncrona.Gets a WaitHandle that is used to wait for an asynchronous operation to complete.

public:
 property System::Threading::WaitHandle ^ AsyncWaitHandle { System::Threading::WaitHandle ^ get(); };
public System.Threading.WaitHandle AsyncWaitHandle { get; }
member this.AsyncWaitHandle : System.Threading.WaitHandle
Public ReadOnly Property AsyncWaitHandle As WaitHandle

Valor da propriedade

Um WaitHandle que é usado para aguardar a conclusão de uma operação assíncrona.A WaitHandle that is used to wait for an asynchronous operation to complete.

Exemplos

O exemplo a seguir demonstra como usar a propriedade AsyncWaitHandle para obter um WaitHandlee como esperar uma chamada assíncrona em um delegado.The following example demonstrates how to use the AsyncWaitHandle property to get a WaitHandle, and how to wait for an asynchronous call on a delegate. O WaitHandle é sinalizado quando a chamada assíncrona é concluída, e você pode esperar por ele chamando o método WaitOne.The WaitHandle is signaled when the asynchronous call completes, and you can wait for it by calling the WaitOne method.

O exemplo consiste em duas classes: a classe que contém o método que é chamado de forma assíncrona e a classe que contém o método Main que faz a chamada.The example consists of two classes: the class that contains the method that is called asynchronously, and the class that contains the Main method that makes the call.

Para obter mais informações e mais exemplos de como chamar métodos de forma assíncrona usando delegados, consulte chamando métodos síncronos de formaassíncrona.For more information and more examples of calling methods asynchronously by using delegates, see Calling Synchronous Methods Asynchronously.

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);
}}}
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);
}
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 <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.".
 */
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.".
 */
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.".

Comentários

O valor de retorno permite que o cliente aguarde a conclusão de uma operação assíncrona em vez de sondar IsCompleted até que a operação seja concluída.The return value allows the client to wait for an asynchronous operation to complete instead of polling IsCompleted until the operation concludes. O valor de retorno pode ser usado para executar uma operação WaitOne, WaitAnyou WaitAll.The return value can be used to perform a WaitOne, WaitAny, or WaitAll operation.

O Common Language Runtime fornece vários objetos que esperam, como ManualResetEvent, AutoResetEvente Mutex, todos os primitivos de sincronização do Win32 do espelho.The common language runtime supplies a number of waitable objects, such as ManualResetEvent, AutoResetEvent, and Mutex, all of which mirror Win32 synchronization primitives.

Notas aos Implementadores

O objeto que implementa IAsyncResult não precisa criar o WaitHandle até que a propriedade AsyncWaitHandle seja lida.The object that implements IAsyncResult does not need to create the WaitHandle until the AsyncWaitHandle property is read. É a opção do implementador de IAsyncResult.It is the choice of the IAsyncResult implementer. No entanto, se o implementador criar AsyncWaitHandle, é responsabilidade do implementador sinalizar o WaitHandle que encerrará a espera no momento apropriado.However, if the implementer creates AsyncWaitHandle, it is the responsibility of the implementer to signal the WaitHandle that will terminate the wait at the appropriate time. Por exemplo, AsyncResult encerra a espera em nome do chamador quando um método invocado de forma assíncrona retorna.For example, AsyncResult terminates the wait on behalf of the caller when an asynchronously invoked method returns. Depois de criada, AsyncWaitHandle deve ser mantida ativa até que o usuário chame o método que conclui a operação assíncrona.Once created, AsyncWaitHandle should be kept alive until the user calls the method that concludes the asynchronous operation. Nesse momento, o objeto por trás de AsyncWaitHandle pode ser Descartado.At that time the object behind AsyncWaitHandle can be discarded.

Notas aos Chamadores

Os clientes que aguardam a conclusão da operação (em oposição à sondagem) usam essa propriedade para obter um objeto de sincronização a ser aguardado.Clients that wait for the operation to complete (as opposed to polling) use this property to obtain a synchronization object to wait on.


Quando você usa o método BeginInvoke de um delegado para chamar um método de forma assíncrona e obter um identificador de espera do IAsyncResultresultante, recomendamos que você feche o identificador de espera assim que terminar de usá-lo, chamando o método Close().When you use the BeginInvoke method of a delegate to call a method asynchronously and obtain a wait handle from the resulting IAsyncResult, we recommend that you close the wait handle as soon as you are finished using it, by calling the Close() method. Se você simplesmente liberar todas as referências para o identificador de espera, os recursos do sistema serão liberados quando a coleta de lixo recuperar o identificador de espera, mas a coleta de lixo funcionará com mais eficiência quando objetos descartáveis forem explicitamente fechados ou descartados.If you simply release all references to the wait handle, system resources are freed when garbage collection reclaims the wait handle, but garbage collection works more efficiently when disposable objects are explicitly closed or disposed. Para obter mais informações, consulte a propriedade AsyncWaitHandle.For more information, see the AsyncWaitHandle property.

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