等待多个回调

Question

我正在使用一个执行异步调用的库,当返回响应时,将调用带有结果的回调方法.这是一个简单的模式,但我现在遇到了障碍.如何对异步方法进行多次调用并等待(不阻塞)它们？当我从所有服务获得数据时,我想调用我自己的回调方法,该方法将获得异步方法返回的两个(或更多)值.

这里遵循的正确模式是什么？顺便说一句,我不能改变库使用TPL或其他东西......我必须忍受它.

public static void GetDataAsync(Action<int, int> callback)
{
    Service.Instance.GetData(r1 =>
    {
        Debug.Assert(r1.Success);
    });

    Service.Instance.GetData2(r2 =>
    {
        Debug.Assert(r2.Success);
    });

    // How do I call the action "callback" without blocking when the two methods have finished to execute?
    // callback(r1.Data, r2.Data);
}

Answer 1

你想要的是像CountdownEvent.试试这个(假设您使用的是.NET 4.0):

public static void GetDataAsync(Action<int, int> callback)
{
    // Two here because we are going to wait for 2 events- adjust accordingly
    var latch = new CountdownEvent(2);

    Object r1Data, r2Data;    

    Service.Instance.GetData(r1 =>
    {
        Debug.Assert(r1.Success);
        r1Data = r1.Data;
        latch.Signal();
    });

    Service.Instance.GetData2(r2 =>
    {
        Debug.Assert(r2.Success);
        r2Data = r2.Data;
        latch.Signal();
    });

    // How do I call the action "callback" without blocking when the two methods have finished to execute?
    // callback(r1.Data, r2.Data);

    ThreadPool.QueueUserWorkItem(() => {
        // This will execute on a threadpool thread, so the 
        // original caller is not blocked while the other async's run

        latch.Wait();
        callback(r1Data, r2Data);
        // Do whatever here- the async's have now completed.
    });
}