这是使用Parallel.ForEach的（）是线程安全的？ [英] Is this use of Parallel.ForEach() thread safe?

问题描述

从本质上讲，我与这方面的工作：

Essentially, I am working with this:

var data = input.AsParallel();
List<String> output = new List<String>();

Parallel.ForEach<String>(data, line => {
    String outputLine = ""; 
    // ** Do something with "line" and store result in "outputLine" **

    // Additionally, there are some this.Invoke statements for updating UI

    output.Add(outputLine);
});

输入一个列表与LT;弦乐＆GT; 对象。在的ForEach（）语句进行一些处理上的每个值，更新UI，并将结果添加到输出 列表。有什么内在的错误呢？

Input is a List<String> object. The ForEach() statement does some processing on each value, updates the UI, and adds the result to the output List. Is there anything inherently wrong with this?

注：

• 输出顺序的不重要

• Output order is unimportant

更新：

根据反馈，我已经得到了，我添加了一个手动锁定到 output.Add 语句，以及到UI更新code

Based on feedback I've gotten, I've added a manual lock to the output.Add statement, as well as to the UI updating code.

推荐答案

是的; 列表＆LT; T＆GT; 不是线程安全的，所以增加了它特设免遭任意线程（很可能在同一时间）是注定的。你应该使用一个线程安全的列表，而不是，或添加手动锁定。或者，也许有一个 Parallel.ToList 。

Yes; List<T> is not thread safe, so adding to it ad-hoc from arbitrary threads (quite possibly at the same time) is doomed. You should use a thread-safe list instead, or add locking manually. Or maybe there is a Parallel.ToList.

另外，如果它的问题：插入顺序将得不到保证。

Also, if it matters: insertion order will not be guaranteed.

该版本的是的安全，虽然：

This version is safe, though:

var output = new string[data.Count];

Parallel.ForEach<String>(data, (line,state,index) =>
{
    String outputLine = index.ToString();
    // ** Do something with "line" and store result in "outputLine" **

    // Additionally, there are some this.Invoke statements for updating UI
    output[index] = outputLine;
});

在这里我们使用首页更新每个并行调用不同的数组索引。

here we are using index to update a different array index per parallel call.

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