From: 011netservice@gmail.com
Date: 2022-04-24
Subject: IAsyncResult.txt

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20201106

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 that 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.

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 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.".
 */
 
 
Remarks
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 it is passed to 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.


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20200811

/*

ZAsyncResult.cs

非同步方法回傳結果.
IAsyncResult 無法直接回傳, 所以可以透過實作 IAsyncResult 的物件回傳.

https://stackoverflow.com/questions/54342202/how-to-implement-an-interface-returns-iasyncresult-with-empty-method-body

Resolved by Adding an IAsyncResult implementation as a completed async result

internal class CompletedAsyncResult : IAsyncResult
{
    public CompletedAsyncResult(object state)
    {
        this.AsyncState = state;
    }

    public object AsyncState { get; set; }
    public WaitHandle AsyncWaitHandle => new ManualResetEvent(true);
    public bool CompletedSynchronously => true;
    public bool IsCompleted => true;
}
and used like

protected override IAsyncResult OnBeginOpen(TimeSpan timeout, AsyncCallback callback, object state)
{
    var result = new CompletedAsyncResult(state); // 將狀態物件放進 CompletedAsyncResult
    callback?.Invoke(result); // 交給 Callback 處理狀態物件
    return result;  // 回傳 符合IAsyncResult 的  CompletedAsyncResult 物件.
}


*/

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading;
using System.Threading.Tasks;

namespace ZLib.DThread
{
    /// <summary>
    /// 實作 IAsyncResult 的物件, 可做為 IAsyncResult 的回傳值.
    /// </summary>
    public class ZAsyncResult : IAsyncResult
    {
        public ZAsyncResult(object State)
        {
            MState = State;
        }

        object MState;

        #region IAsyncResult implements
        public object AsyncState
        {
            get
            {
                return MState;
            }
        }

        // Lambda: public WaitHandle AsyncWaitHandle => new ManualResetEvent(true);
        public WaitHandle AsyncWaitHandle
        {
            get
            {
                return new ManualResetEvent(true);
            }
        }

        // Lambda: public bool CompletedSynchronously => true;
        public bool CompletedSynchronously
        {
            get
            {
                return true;
            }
        }

        // Lambda: public bool IsCompleted => true;
        public bool IsCompleted
        {
            get
            {
                return true;
            }
        }
        #endregion
    }
}