扩展方法线程安全吗?:Is Extension method thread safe?

此扩展方法线程安全吗?

Is this Extension method thread safe?

 public static class Extensions { public static void Raise<T>(this EventHandler<T> handler, object sender, T args) where T : EventArgs { if (handler != null) handler(sender, args); } } 

还是我需要将其更改为此?

or do I need to change it to this?

 public static class Extensions { public static void Raise<T>(this EventHandler<T> handler, object sender, T args) where T : EventArgs { var h = handler; if (h!= null) h(sender, args); } } 

问题解答

您发现了一个有趣的循环漏洞，它使所有人绊倒了.不，它不是线程安全的.

You found an interesting loop hole, it tripped everybody up. No, it is not thread-safe.

看起来就像通过方法参数复制了EventHandler<>引用一样，但在运行时不会发生这种情况.扩展方法需要内联，就像常规实例方法一样.实际上，由于它很小，很可能非常被内联.没有副本，您必须自己制作.

While it looks like the EventHandler<> reference is copied through the method argument, this is not what happens at runtime. Extension methods are subject to being inlined, just like a regular instance method. In fact, it is extremely likely to get inlined since it is so small. There's no copy, you have to make one yourself.

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