event复制，怎么不work？

miccjiang

标准里面这段后面还有一段：
When events are merged, the assignment only affects the execution of subsequent event control or wait
operations. If a process is blocked waiting for event1 when another event is assigned to event1, the
currently waiting process shall never unblock.
所以如果由正在等待event1的线程，而 event1被赋予event2，此时等待event1的线程将不会unblock；
所以如果想要ev_b等待线程能执行, ev_b = ev_a的执行必须要在wait(ev_b.triggered)之前；