C#，MultiThread Lambda 是否使用自由变量有效？

Question

我想在多线程 Lambda 表达式中使用一些自由变量。

这里是例子，

{
   int a = 0;
   Thread t = new Thread(() => 
   {
        SomeBlockingFunc(a);
   });
   t.Start();
}

无法识别线程何时执行，即使变量作用域已结束。

即使在范围结束后，'int a' 是否有效？

谢谢。

Answer 1

lambda 表达式捕获 a 变量。此代码完全有效。

来自 C# 6 规范草案，section 11.16.6.2：

When an outer variable is referenced by an anonymous function, the outer variable is said to have been captured by the anonymous function. Ordinarily, the lifetime of a local variable is limited to execution of the block or statement with which it is associated (§9.2.8). However, the lifetime of a captured outer variable is extended at least until the delegate or expression tree created from the anonymous function becomes eligible for garbage collection.

区分变量的 scope 和 lifetime 很重要 的变量。

还值得注意的是，它确实仍然是一个变量。多个委托可能会捕获相同的变量。考虑这段代码：

using System;

int value = 0;
Action a = () =>
{
    Console.WriteLine($"In first action; value={value}");
    value++;
};
Action b = () =>
{
    Console.WriteLine($"In second action; value={value}");
    value++;
};

a();
a();
b();
a();

这个输出是：

In first action; value=0
In first action; value=1
In second action; value=2
In first action; value=3

如您所见：

两个动作捕获了同一个变量
两个操作都可以看到每个操作中对变量值所做的更改

C#，MultiThread Lambda 是否使用自由变量有效？

C#, is MultiThread Lambda using free variable Valid?

c#

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free-variable