这个函数创建一个手工重置或自动重置的事件对象，同时还要设置改对象的初始状态。

This function creates a manual-reset or auto-reset event object and also sets the initial state of the object.

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通知还可以用于触发事件，如对于超过设置阀值(比如内存或者磁盘空间等资源不足)的状态改变做出反应。

Notification can also be used to trigger events, such as reacting to a state change that surpasses a given threshold, as in the case of dwindling resources like memory or disk space.

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对一个已经设置为有信号状态的事件对象再次执行该函数是无效的。

Setting an already-set event object has no effect .

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