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AsyncResult Class

Encapsulates the results of an asynchronous operation on a delegate.


Namespace:  System.Runtime.Remoting.Messaging
Assembly:  mscorlib (in mscorlib.dll)

<ComVisibleAttribute(True)> _
Public Class AsyncResult _
	Implements IAsyncResult, IMessageSink

The AsyncResult type exposes the following members.

Public propertyAsyncDelegateGets the delegate object on which the asynchronous call was invoked.
Public propertyAsyncStateGets the object provided as the last parameter of a BeginInvoke method call.
Public propertyAsyncWaitHandleGets a WaitHandle that encapsulates Win32 synchronization handles, and allows the implementation of various synchronization schemes.
Public propertyCompletedSynchronouslyGets a value indicating whether the BeginInvoke call completed synchronously.
Public propertyEndInvokeCalledGets or sets a value indicating whether EndInvoke has been called on the current AsyncResult.
Public propertyIsCompletedGets a value indicating whether the server has completed the call.
Public propertyNextSinkGets the next message sink in the sink chain.

Public methodAsyncProcessMessageImplements the IMessageSink interface.
Public methodEquals(Object)Determines whether the specified Object is equal to the current Object. (Inherited from Object.)
Protected methodFinalizeAllows an object to try to free resources and perform other cleanup operations before it is reclaimed by garbage collection. (Inherited from Object.)
Public methodGetHashCodeServes as a hash function for a particular type. (Inherited from Object.)
Public methodGetReplyMessageGets the response message for the asynchronous call.
Public methodGetTypeGets the Type of the current instance. (Inherited from Object.)
Protected methodMemberwiseCloneCreates a shallow copy of the current Object. (Inherited from Object.)
Public methodSetMessageCtrlSets an IMessageCtrl for the current remote method call, which provides a way to control asynchronous messages after they have been dispatched.
Public methodSyncProcessMessageSynchronously processes a response message returned by a method call on a remote object.
Public methodToStringReturns a string that represents the current object. (Inherited from Object.)

The AsyncResult class is used in conjunction with asynchronous method calls made using delegates. The IAsyncResult returned from the delegate's BeginInvoke method can be cast to an AsyncResult. The AsyncResult has the AsyncDelegate property that holds the delegate object on which the asynchronous call was invoked.

For more information about BeginInvoke and asynchronous calls using delegates, see Asynchronous Programming Using Delegates.

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. The WaitHandle is signaled when the asynchronous call completes, and you can wait for it by calling the WaitOne method.

The example consists of two classes, the class that contains the method which is called asynchronously, and the class that contains the Main method that makes the call.

For more information and more examples of calling methods asynchronously by using delegates, see Calling Synchronous Methods Asynchronously.

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.")
            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


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)

            Console.WriteLine("Main thread {0} does some work.", _
            ' Perform additional processing here and then
            ' wait for the WaitHandle to be signaled.

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

            ' Close the wait handle.

            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.".

.NET Framework

Supported in: 4, 3.5, 3.0, 2.0, 1.1, 1.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.