c# - .NET lambda 是否会阻止对其中使用的外部引用进行垃圾回收？

Question

这是一个例子:

var task = Task.Run();
var func = () => task.Result;

因此，如果我松开任务引用并保留函数引用，GC 是否会收集任务并使函数抛出空引用异常？

Answer 1

没有。匿名函数捕获变量，将其生命周期至少延长到委托(delegate)或表达式树被垃圾回收时。

来自 C# 5 规范，第 7.15.5.1 节:

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 (§5.1.7). 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.

请注意，捕获的是变量，而不是当时变量的值。因此，如果您将代码更改为:

var task = Task.Run(...);
var func = () => task.Result;
task = null;

...那么原始的 Task 可以被垃圾回收，如果你调用它，委托(delegate)会抛出异常，因为它会使用 current task 变量的值。