使用不同的参数并行运行相同的代码多次 [英] Run same code multiple times in parallel with different parameter

问题描述

这个非常简单的例子:

        int numLanes = 8;
        var tasks = new List<Task>();
        for (var i = 0; i < numLanes; ++i)
        {
            var t = new Task(() =>
            {
                Console.WriteLine($"Lane {i}");
            });
            tasks.Add(t);
        }
        tasks.ForEach((t) => t.Start());
        Task.WaitAll(tasks.ToArray());

产生:

Lane 8
Lane 8
Lane 8
Lane 8
Lane 8
Lane 8
Lane 8
Lane 8

这与预期不同，参数 i 未正确传递.我曾想过使用 Action 来包装代码，但不知道我会怎么做.我不想编写像 Task CreateTask(int i) 这样的专用方法，我对如何使用 lambdas 感兴趣.

Which is not as expected, the parameter i isn't passed correctly. I had thought to use Action<int> to wrap the code but couldn't see how I would. I do not want to write a dedicated method like Task CreateTask(int i) I'm interested how to do it using lambdas.

执行此操作的正常方法是什么 - 使用不同的参数值并行运行相同的代码多次?

What is normal way to do this - spin up the same code a bunch of times in parallel with a different parameter value?

推荐答案

您有一个捕获的循环变量 i，尝试在循环中添加临时变量并将其传递给 任务

You've got a captured loop variable i, try to add temp variable inside a loop and pass it to the Task

for (var i = 0; i < numLanes; ++i)
{
    var temp = i;
    var t = new Task(() =>
    {
        Console.WriteLine($"Lane {temp}");
    });
    tasks.Add(t);
}

进一步阅读如何在 C# 中捕获变量而不是射中自己.foreach 循环在 C# 5 之前具有相同的行为，但根据上面的链接

Further reading How to capture a variable in C# and not to shoot yourself in the foot. foreach loop has the same behavior before C# 5, but according to link above

随着 C# 5.0 标准的发布，这种行为被改变了在每次循环迭代中声明迭代器变量，而不是在编译阶段之前，但对于所有其他结构类似的行为保持不变

with the release of the C# 5.0 standard this behavior was changed by declaring the iterator variable inside every loop iteration, not before it on the compilation stage, but for all other constructions similar behavior remained without any changes

因此，您可以使用 foreach 而不使用临时变量

So, you may use foreach without temp variable

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