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.
    });
}

Answer 2

您可以对您进行的每次异步通话使用Interlocked.Increment。完成后，调用Interlocked.Decrement并检查零，如果为零，则调用您自己的回调。您需要将r1和r2存储在回调代理之外。

等待多个回调

2 个答案: