如何正确取消Parallel.Foreach?

问题描述

我有看起来像这样的代码:

I've got code which looks something like this:

Parallel.Foreach(ItemSource(),(item)=>DoSomething(item));

ItemSource()产生无限的项目流.

我希望一旦满足某些条件就退出循环，我希望这样做不会在DoSomething中引发异常(我认为这种方法是不好的编程风格).

I want the loop to exit once some condition has been met, and I'd rather do it without throwing an exception in DoSomething (I consider this approach a bad programming style).

理想情况下，会有诸如cancelleToken之类的东西.我会在一个或多个线程中调用cancelToken.Activate()，此后parallel.foreach将停止创建新线程，并且在最后一个线程退出后，该函数将返回.

Ideally, there would be something like cancellationToken. I would call cancellationToken.Activate() in one or more threads, after which parallel.foreach would stop creating new threads and after the last thread has exited, the function would return.

这是否可以在Parallel.ForEach的c#中完成，还是应该使用线程insteag?

Is this possible to do in c# with Parallel.ForEach, or should I use threads insteag?

更新这是微软建议的方式我做到了:

        try
        {
            Parallel.ForEach(nums, po, (num) =>
            {
                double d = Math.Sqrt(num);
                Console.WriteLine("{0} on {1}", d, Thread.CurrentThread.ManagedThreadId);
                po.CancellationToken.ThrowIfCancellationRequested();
            });
        }
        catch (OperationCanceledException e)
        {
            Console.WriteLine(e.Message);
        }

我不喜欢这种方法，因为它涉及到在委托内部抛出异常.

I don't like this approach, because it involves throwing exception inside the delegate.

推荐答案

在Parallel.ForEach中，有一个创建ParallelLoopState的选项，该状态使您可以打破循环:

In Parallel.ForEach there is an option to create a ParallelLoopState this state allows you to break the loop:

ParallelOptions po = new ParallelOptions();
po.MaxDegreeOfParallelism = Constants.MaxParallelProcesses;
var drc = Companies.AsEnumerable();

Parallel.ForEach(drc, po, (drcCompany, loopState) =>
{
    //do stuff here
    if(YourBreakCondition) loopState.Break();
}

在此处 http://msdn.microsoft.com/es-es/library/system.threading.tasks.parallelloopstate.aspx

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