.net - 为远程调用实现 Task<T> 而不是在事件中响应？

Question

我有一个 API，其界面如下所示:

void SendRequest(Guid id, IRequest request);
event EventHandler<ResponseEventArgs> ResponseReceived;

实现此方法的最佳方式是什么？

Task<T> GetResponse(IRequest request) where T: IRequest

请注意，多个请求可能会相互重叠，因此当响应返回时，我需要查找父请求。我有一种感觉 TaskCompletionSource 可能有用，但不能完全拼凑起来。

Answer 1

编辑:

如果您想在不阻塞线程的情况下执行此操作，您可以使用 TaskCompletionSource<T> 执行类似的操作:

var completionSource = new TaskCompletionSource<T>();

var requestIdentifier = Guid.NewGuid();

EventHandler<ResponseEventArgs> handler = null;

handler = (sender, args) =>
{
    if(args.RequestIdentifier == requestIdentifier)
    {
        api.ResponseReceived -= handler; 

        // TrySetResult avoids re-entrancy problems in case of an
        // API that sends duplicates, but there other ways of 
        // dealing with this too.
        completionSource.TrySetResult((T)args.Response);
    }      
};


api.ResponseReceived += handler; 

// Make this async if you want.
api.SendRequest(requestIdentifier, request); 

return completionSource.Task;

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原始答案:

我想你想要类似下面的东西，它使用 ManualResetEvent 阻塞线程，直到 API 引发事件:

return Task.Factory.StartNew<T>(() =>
{
    var waitHandle = new ManualResetEvent(false);

    T result = default(T);

    var requestIdentifier = Guid.NewGuid();

    EventHandler<ResponseEventArgs> handler = (sender, args) =>
    {
         if(args.RequestIdentifier == requestIdentifier)
         {
             result = (T)args.Response; // Not sure how this looks in your API
             waitHandle.Set(); // Unblock the thread running the task     
         }      
    };

    // Attach handler to respond to the response being received.
    api.ResponseReceived += handler; 

    // Send request off.
    api.SendRequest(requestIdentifier, request); 

    // Wait until response is received.
    waitHandle.WaitOne(); 

    // Detach handler to prevent leak.
    api.ResponseReceived -= handler; 

    return result;
});

---

要获得更简洁的方法，请查看 Reactive Extensions .