如何打破 C# 中的内部嵌套 Parallel.Foreach 循环？

Question

为什么这个 break 语句不起作用？我的目标是只跳出内循环，但继续处理外循环。无论我做什么，它都会击中Console.WriteLine()。

我试过了：

1. innerLoopState.Break()
2. innerLoopState.Stop()

在Console.WriteLine()之前不要停止循环...

private static ParallelOptions ParallelCityOptions => new ParallelOptions
{
    MaxDegreeOfParallelism = 2
};

private static ParallelOptions ParallelPeopleOptions => new ParallelOptions
{
    MaxDegreeOfParallelism = 3
}

[Test]
public void NestedParallelForeach()
{
    var listOfCities = new List<string> {"Atlanta", "Denver", "Scranton",};
    var listOfPeople = new List<string>() {"Bob", "Sally", "Craig", "Bill"};

    Parallel.ForEach(listOfCities, ParallelCityOptions, city =>
    {
        Parallel.ForEach(listOfPeople, ParallelPeopleOptions, (person, innerLoopState) =>
        {

            if (person == "Bill")
            {
                // do something
                innerLoopState.Break();
                Console.WriteLine("Should never hit this line.");
            }
        });
    });
}

Answer 1

你的问题的直接答案是：咖喱外循环状态并按你的意愿打破它：

Parallel.ForEach(listOfCities, ParallelCityOptions, (city, outerLoopState) =>
{
    Parallel.ForEach(listOfPeople, ParallelPeopleOptions, (person, innerLoopState) =>
    {

        if (person == "Bill")
        {
            // do something
            outerLoopState.Break();
            innerLoopState.Break();
            Console.WriteLine("Should never hit this line.");
        }
    });
});

但是，数组中的所有元素都将由您的代码一次处理，因为与现代计算机的内核数量相比，内核数量太少了。简单地请求并行循环中断不会神奇地中断所有线程，它只会阻止新线程的处理。