java - 这个等待通知线程语义的真正目的是什么？

Question

我刚刚遇到一些代码，这些代码使用 wait-notify 构造通过其其他成员方法与类中定义的线程进行通信。 有趣的是，获取锁后，同步范围内的所有线程都会在同一锁上进行定时等待(请参见下面的代码片段)。稍后，在非同步作用域中，线程执行其关键函数(即'//do some important1')。

我对此机制的目的的最佳猜测是，最大限度地减少线程的资源消耗，直到其他线程调用“someMethod”。专家有何看法？如果是这种情况，实现这种行为的更好方法是什么？

class SomeClass{
    public void run() {
        while (!isShuttingDown){
            try {
                synchronized (SomeClass.class) {
                    SomeClass.class.wait(500);
                }
            } catch (Throwable e) {
                LOGGER.info(SomeClass.class.getSimpleName() + " reaper thread interrupted", e);
            }
            //do something useful1
          }
    }


    public synchronized void someMethod(){
            //do something useful2
             synchronized (SomeClass.class) {
                SomeClass.class.notifyAll();
            }   
                   //do something useful3
    }
}

Answer 1

如上所述here ,

The wait-notify pattern is used in a broad set of cases where one thread needs to tell other threads that some event has occurred. It is commonly used to implement a thread pool or producer-consumer scenario, where a particular thread or threads need to "pick up jobs" created by other threads (in this case, the "event" that has occurred is that a job has arrived for one of the threads to pick up).