如何在异步调用报告超时？ [英] How to report timeout in Asynchronous call?

问题描述

我学习threading.My强度在一定值传递给计算方法，如果结果不会20毫秒内返回，我将报告操作超时。基于我understading我已经实现了code如下：

I am learning threading.My intension is to pass some values to a method for calculation,if the result will not be returned within 20 ms,i will report "Operation timeout".Based on my understading i have implemented the code as follows:

public delegate long CalcHandler(int a, int b, int c);


public static void ReportTimeout()
    {
        CalcHandler doCalculation = Calculate;

        IAsyncResult asyncResult = 
        doCalculation.BeginInvoke(10,20,30, null, null);

        if (!asyncResult.AsyncWaitHandle.WaitOne(20, false))
        {
            Console.WriteLine("..Operation Timeout...");
        }

        else
       {
        // Obtain the completion data for the asynchronous method.
        long val;
        try
        {
            val=  doCalculation.EndInvoke(asyncResult);
            Console.WriteLine("Calculated Value={0}", val);
        }
        catch
        {
            // Catch the exception
        }
     }

    } 

public static long Calculate(int a,int b,int c)
     {
        int m;
        //for testing timeout,sleep is introduced here.
        Thread.Sleep(200);
        m = a * b * c;
        return m;
    }

问题：

（1）它是正确的方法来报告超时？

(1) Is it the proper way to report timeout ?

（2）我不会调用EndInvoke（），如果时间out.In这种情况下调用EndInvoke会（）是必须的？

(2) I will not call EndInvoke() ,if the time is out.In such case calling the EndInvoke() is mandatory?

（3）我听说

即使你不想处理您的异步方法的返回值，你应该调用EndInvoke;否则，你可能每次内存泄露你开始使用的BeginInvoke异步调用

什么是记忆相关的风险？你可以给的例子吗？

What is the risk associated with memory ? can you give example ?

推荐答案

答案

（1）通常你刚才扔System.TimeoutException

(1) Usually you just throw System.TimeoutException

（2）原因EndInvoke会（）需要的是，如果返回值（或抛出异常）有内存分配GC可能无法迅速清理。我还没有看到的地方，这是一个大问题的情况......但是这只是我。

(2) The reason EndInvoke() is required is that if return values (or exceptions thrown) have memory allocations the GC may not clean it up as quickly. I have not seen a case where this was a big problem... but that's just me.

如果您真的担心它，你可以只调用ThreadPool.QueueUserWorkItem是的大多的东西上面的异步调用就可以了。 （注：可以在的WinForms或其他线程依赖的环境问题）。反正你可以按照如下运行你自己的工作项目：

If your really worried about it you can just call ThreadPool.QueueUserWorkItem which is mostly what the above async invoke will do. (note: can be a problem in WinForms or other thread-dependent contexts). Anyway you can run your own work item as follows:

	public static long Calc(CalcHandler fn, int a, int b, int c)
	{
		return Run<long>(TimeSpan.FromSeconds(20), delegate { return fn(a, b, c); });
	}

	public static T Run<T>(TimeSpan timeout, Func<T> operation)
	{
		Exception error = null;
		T result = default(T);

		ManualResetEvent mre = new ManualResetEvent(false);
		System.Threading.ThreadPool.QueueUserWorkItem(
			delegate(object ignore)
			{
				try { result = operation(); }
				catch (Exception e) { error = e; }
				finally { mre.Set(); }
			}
		);
		if (!mre.WaitOne(timeout, true))
			throw new TimeoutException();
		if (error != null)
			throw new TargetInvocationException(error);
		return result;
	}

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