IAsyncResult Interface
Assembly: mscorlib (in mscorlib.dll)
The IAsyncResult interface is implemented by classes containing methods that can operate asynchronously. It is the return type of methods that initiate an asynchronous operation, such as FileStream.BeginRead, and is the type of the third parameter of methods that conclude an asynchronous operation, such as FileStream.EndRead. IAsyncResult objects are also passed to methods invoked by AsyncCallback delegates when an asynchronous operation completes.
An object that supports the IAsyncResult interface stores state information for an asynchronous operation, and provides a synchronization object to allow threads to be signaled when the operation completes.
For a detailed description of how the IAsyncResult interface is used, see the Calling Synchronous Methods Asynchronously topic.
The following sample demonstrates using an IAsyncResult to obtain the return value of an asynchronous operation.
' Asynchronous Callback method. Public Shared Sub MyCallback(ar As IAsyncResult) ' Obtains the last parameter of the delegate call. Dim value As Integer = Convert.ToInt32(ar.AsyncState) ' Obtains return value from the delegate call using EndInvoke. Dim aResult As AsyncResult = CType(ar, AsyncResult) Dim temp As SampSyncSqrDelegate = CType(aResult.AsyncDelegate, SampSyncSqrDelegate) Dim result As Integer = temp.EndInvoke(ar) Console.Write("Simple.SomeMethod (AsyncCallback): Result of ") Console.WriteLine("{0} in SampleSynchronized.Square is {1} ", value, result) End Sub 'MyCallback
// Asynchronous Callback method.
public static void MyCallback(IAsyncResult ar)
{
// Obtains the last parameter of the delegate call.
SampSyncSqrDelegate sampDelg = (SampSyncSqrDelegate)ar.get_AsyncState();
// Obtains return value from the delegate call using EndInvoke.
AsyncResult aResult = (AsyncResult)ar;
SampSyncSqrDelegate temp =
(SampSyncSqrDelegate)(aResult.get_AsyncDelegate());
int threadId = AppDomain.GetCurrentThreadId();
int result = temp.EndInvoke(ar);
Console.Write("Simple.SomeMethod (AsyncCallback): Result of ");
Console.WriteLine("{0} in SampleSynchronized.Square is {1} ",
(Int32)value, (Int32)result);
} //MyCallback
The following sample demonstrates waiting for an asynchronous operation to complete.
Imports System Imports System.Threading Imports System.Runtime.Remoting Imports System.Runtime.Remoting.Contexts Imports System.Runtime.Remoting.Messaging ' ' Context-Bound type with Synchronization Context Attribute ' <Synchronization()> Public Class SampleSyncronized Inherits ContextBoundObject ' A method that does some work - returns the square of the given number Public Function Square(i As Integer) As Integer Console.Write("SampleSyncronized.Square called. ") Console.WriteLine("The hash of the current thread is: {0}", Thread.CurrentThread.GetHashCode()) Return i * i End Function 'Square End Class 'SampleSyncronized ' ' Async delegate used to call a method with this signature asynchronously ' Delegate Function SampSyncSqrDelegate(i As Integer) As Integer 'Main sample class Public Class AsyncResultSample Public Shared Sub Main() Dim callParameter As Integer = 0 Dim callResult As Integer = 0 'Create an instance of a context-bound type SampleSynchronized 'Because SampleSynchronized is context-bound, the object sampSyncObj 'is a transparent proxy Dim sampSyncObj As New SampleSyncronized() 'call the method synchronously Console.Write("Making a synchronous call on the object. ") Console.WriteLine("The hash of the current thread is: {0}", Thread.CurrentThread.GetHashCode()) callParameter = 10 callResult = sampSyncObj.Square(callParameter) Console.WriteLine("Result of calling sampSyncObj.Square with {0} is {1}.", callParameter, callResult) Console.WriteLine("") Console.WriteLine("") 'call the method asynchronously Console.Write("Making an asynchronous call on the object. ") Console.WriteLine("The hash of the current thread is: {0}", Thread.CurrentThread.GetHashCode()) Dim sampleDelegate As New SampSyncSqrDelegate(AddressOf sampSyncObj.Square) callParameter = 17 Dim aResult As IAsyncResult = sampleDelegate.BeginInvoke(callParameter, Nothing, Nothing) 'Wait for the call to complete aResult.AsyncWaitHandle.WaitOne() callResult = sampleDelegate.EndInvoke(aResult) Console.WriteLine("Result of calling sampSyncObj.Square with {0} is {1}.", callParameter, callResult) End Sub 'Main End Class 'AsyncResultSample
Windows 98, Windows 2000 SP4, Windows CE, Windows Millennium Edition, Windows Mobile for Pocket PC, Windows Mobile for Smartphone, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition
The .NET Framework does not support all versions of every platform. For a list of the supported versions, see System Requirements.