在事件调度之前检查空值...线程安全吗?

问题描述

令我困惑但从未引起任何问题的东西...推荐的事件调度方式如下:

Something that confuses me, but has never caused any problems... the recommended way to dispatch an event is as follows:

public event EventHandler SomeEvent;
...
{
    ....
    if(SomeEvent!=null)SomeEvent();
}

在多线程环境中，这段代码如何保证另一个线程在检查空值和调用事件之间不会改变SomeEvent的调用列表?

In a multi-threaded environment, how does this code guarantee that another thread will not alter the invocation list of SomeEvent between the check for null and the invocation of the event?

推荐答案

在 C# 6.0 中，您可以使用 monadic Null 条件运算符 ?. 以简单且线程安全的方式检查 null 并引发事件方式.

In C# 6.0 you can use monadic Null-conditional operator ?. to check for null and raise events in easy and thread-safe way.

SomeEvent?.Invoke(this, args);

它是线程安全的，因为它只计算左侧一次，并将其保存在一个临时变量中.您可以部分阅读此处标题为空条件运算符.

It’s thread-safe because it evaluates the left-hand side only once, and keeps it in a temporary variable. You can read more here in part titled Null-conditional operators.

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