与Parallel.ForEach产量返回线程安全（） [英] Thread safety of yield return with Parallel.ForEach()

问题描述

考虑下面的代码示例，它创建一个整数枚举集合并同时对其进行处理：

Consider the following code sample, which creates an enumerable collection of integers and processes it in parallel:

using System.Collections.Generic;
using System.Threading.Tasks;

public class Program
{
    public static void Main()
    {
        Parallel.ForEach(CreateItems(100), item => ProcessItem(item));
    }

    private static IEnumerable<int> CreateItems(int count)
    {
        for (int i = 0; i < count; i++)
        {
            yield return i;
        }
    }

    private static void ProcessItem(int item)
    {
        // Do something
    }
}

能够保证所有的由 Parallel.ForEach（）每得到一个不同的项目或者是周围的增量部分锁定机制和我要求？

Is it guaranteed that the worker threads generated by Parallel.ForEach() each get a different item or is some locking mechanism around incrementation and returning of i required?

推荐答案

Parallel.ForEach< TSource> ，当 TSource 是的IEnumerable< T> ，会为的IEnumerable℃的分区; T> ，它包含自己的的内部锁定机制，这样你就不会需要实现你的迭代任何线程安全。

Parallel.ForEach<TSource>, when TSource is an IEnumerable<T>, creates a partitioner for the IEnumerable<T> that includes its own internal locking mechanism, so you don't need to implement any thread-safety in your iterator.

每当一个辅助线程请求项目的块，分区程序将创建一个内部枚举的，其中：

Whenever a worker thread requests a chunk of items, the partitioner will create an internal enumerator, which:

1. 获取共享锁


2. 通过源迭代（从那里留下的）来获取项目的块，节省了在私人数组项


3. 解除锁定，以便其他块请求可以被满足。


4. 供应来自其私人阵列的工作线程。

1. acquires a shared lock
2. iterates through the source (from where it was left of) to retrieve the chunk of items, saving the items in an private array
3. releases the lock so that other chunk requests can be fulfilled.
4. serves the worker thread from its private array.

正如你所见，在运行通过在的IEnumerable< T> 进行分区的目的是顺序（通过共享锁访问），以及分区并行处理

As you see, the run through the IEnumerable<T> for the purposes of partitioning is sequential (accessed via a shared lock), and the partitions are processed in parallel.

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