实施明确的IAsyncResult

问题描述

我一般警惕部分实现接口的。然而，的IAsyncResult 是一个有点特殊情况，因为它支持多种完全不同的使用模式。你多久使用/看到使用了 AsyncState / 的AsyncCallback 模式，而不是只调用 EndInvoke会，使用 AsyncWaitHandle ，或轮询 IsCompleted （呸）？

I am generally wary of implementing interfaces partially. However, IAsyncResult is a bit of a special case, given that it supports several quite different usage patterns. How often do you use/see used the AsyncState/AsyncCallback pattern, as opposed to just calling EndInvoke, using AsyncWaitHandle, or polling IsCompleted (yuck)?

相关问题：Detecting一个线程池工作项目已经完成/等待完成。

考虑这个类（非常近似的，锁定需要）：

Consider this class (very approximate, locking needed):

public class Concurrent<T> {
    private ManualResetEvent _resetEvent;
    private T _result;

    public Concurrent(Func<T> f) {
        ThreadPool.QueueUserWorkItem(_ => {
                                         _result = f();
                                         IsCompleted = true;
                                         if (_resetEvent != null)
                                             _resetEvent.Set();
                                     });
    }

    public WaitHandle WaitHandle {
        get {
            if (_resetEvent == null)
                _resetEvent = new ManualResetEvent(IsCompleted);
            return _resetEvent;
        }

    public bool IsCompleted {get; private set;}
    ...

它的WaitHandle （懒洋洋地创建，就像的IAsyncResult 描述文档）和 IsCompleted ，但我没有看到 AsyncState 一个合理的实现（ {返回NULL;} ？）。因此，是否有意义为它实施的IAsyncResult ？需要注意的是工作中的并行扩展库并实施的IAsyncResult ，但只有 IsCompleted 是隐式实现的。

It has WaitHandle (lazily created, just as described in IAsyncResult documentation) and IsCompleted, but I don't see a sensible implementation for AsyncState ({return null;}?). So does it make sense for it to implement IAsyncResult? Note that Task in the Parallel Extensions library does implement IAsyncResult, but only IsCompleted is implemented implicitly.

推荐答案

• 在我的经验中，只调用EndInvoke会没有任何等待或正在召回首先是很少有用


• 只是提供回调有时是不够的，因为你的客户可能想同时等待多个操作（了WaitAny，为WaitAll）


• 我从来没有调查IsCompleted，呸哉！所以，你可以节省IsCompleted的实施，但它是如此简单，它似乎不值得震惊的潜在客户。

所以，对于一个异步调用方法的合理的实施确实应该提供一个全面实施的IAsyncResult。

So, a reasonable implementation for an asynchronously callable method should really provide a fully implemented IAsyncResult.

顺便说一句，你往往不需要实现的IAsyncResult自己，只是返回什么是Delegate.BeginInvoke返回。见System.IO.Stream.BeginRead执行的例子。

BTW, you often don't need to implement IAsyncResult yourself, just return what is returned by Delegate.BeginInvoke. See the implementation of System.IO.Stream.BeginRead for an example.

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