IAsyncResult.AsyncWaitHandle 屬性

定義

取得 WaitHandle,用來等候非同步作業完成。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

屬性值

WaitHandle,用來等候非同步作業完成。A WaitHandle that is used to wait for an asynchronous operation to complete.

範例

下列範例示範如何使用AsyncWaitHandle屬性來WaitHandle取得, 以及如何等待委派的非同步呼叫。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. 非同步呼叫完成時, WaitHandle 會收到信號,且您可以呼叫 WaitOne 方法來等候它。The WaitHandle is signaled when the asynchronous call completes, and you can wait for it by calling the WaitOne method.

此範例包含兩個類別: 包含非同步呼叫之方法的類別, 以及包含Main進行呼叫之方法的類別。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.

如需詳細資訊以及使用委派以非同步方式呼叫方法的更多範例, 請參閱以非同步方式呼叫同步方法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.".

備註

傳回值可讓用戶端等候非同步作業完成, 而不是輪詢IsCompleted , 直到作業結束為止。The return value allows the client to wait for an asynchronous operation to complete instead of polling IsCompleted until the operation concludes. 傳回值可用於執行WaitOneWaitAnyWaitAll作業。The return value can be used to perform a WaitOne, WaitAny, or WaitAll operation.

通用語言執行時間提供許多可等候物件, 例如ManualResetEventAutoResetEventMutex, 所有鏡像 Win32 同步處理基本專案都是如此。The common language runtime supplies a number of waitable objects, such as ManualResetEvent, AutoResetEvent, and Mutex, all of which mirror Win32 synchronization primitives.

給實施者的注意事項

在讀取IAsyncResult WaitHandle屬性之前AsyncWaitHandle , 不需要建立所要執行的物件。The object that implements IAsyncResult does not need to create the WaitHandle until the AsyncWaitHandle property is read. 這是IAsyncResult實施者的選擇。It is the choice of the IAsyncResult implementer. 不過, 如果實施者建立AsyncWaitHandle了, 則實施WaitHandle者必須負責指示會在適當時間終止等候的。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. 例如, 當AsyncResult非同步叫用的方法傳回時, 會終止代表呼叫端的等候。For example, AsyncResult terminates the wait on behalf of the caller when an asynchronously invoked method returns. 建立之後, AsyncWaitHandle應該保持運作, 直到使用者通話結束非同步作業的方法為止。Once created, AsyncWaitHandle should be kept alive until the user calls the method that concludes the asynchronous operation. 此時可以捨棄物件後AsyncWaitHandle置。At that time the object behind AsyncWaitHandle can be discarded.

給呼叫者的注意事項

等候作業完成的用戶端 (相對於輪詢) 會使用此屬性來取得要等候的同步處理物件。Clients that wait for the operation to complete (as opposed to polling) use this property to obtain a synchronization object to wait on.


當您使用委派BeginInvoke的方法, 以非同步方式呼叫方法, 並從產生IAsyncResult的等候控制碼取得時, 我們建議您在使用完成後立即關閉等候控制碼 (藉由呼叫Close()方法)。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. 如果您只要釋放所有對等候控制碼的參考, 當垃圾收集回收等候控制碼時, 系統資源就會釋出, 但是在明確關閉或處置可處置的物件時, 垃圾收集會更有效率地運作。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. 如需詳細資訊,請參閱 AsyncWaitHandle 屬性 (Property)。For more information, see the AsyncWaitHandle property.

適用於