实现远程调用的任务<t>而不是在事件中响应？</t>

Question

我有一个API，其界面如下所示：

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

实施此方法的最佳方法是什么？

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，但不能把它拼凑在一起。

Answer 1

修改：

如果您想在不阻止线程的情况下执行此操作，可以使用TaskCompletionSource<T>执行此类操作：

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;

---

原始答案：

我认为您需要类似以下的内容，它使用ManualResetEvent来阻止线程，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;
});

---

为了更清洁地执行此操作，请查看Reactive Extensions。

Answer 2

您可以返回等待事件返回的任务：

Task<T> GetResponse<T>() 
{
    T result = default(T);
    ManualResetEvent ev = new ManualResetEvent(false);
    ResponseReceived += (s,e) =>  {     
        result = default(T); /* result = e.Xxx */
        ev.Set();
    };
    return new Task<T>(() => {
        SendRequest(Guid.NewGuid());        
        ev.WaitOne();
        return result;
    });
}