java：wait（），notify（）和synchronized块 [英] java: wait(), notify() and synchronized blocks

问题描述

我了解到调用Object的 wait（）方法将释放对象监视器（如果存在）。

I learned that calling an Object's wait() method will release the object monitor, if present.

但我有一些关于在另一个线程上对此对象调用 notify（）的问题：

But I have some questions regarding calling notify() on this object by another thread:

1. （何时）如果另一个（第3个）线程同时拥有对象监视器，则等待线程会被唤醒吗？

1. (when) will the waiting thread wake up, if another (a 3rd) thread owns the object monitor in the meanwhile?

等待线程唤醒，如果第三个线程在这个对象上叫 wait（）？

will the waiting thread wake up, if a 3rd thread called wait() on this object?

是不是可以确定线程是否在等待通知特定对象（java 1.4 / java 5）

is it possible to determine if a thread is waiting for notifying a particular object (java 1.4/java 5)

如果 wait（）会发生什么将在 finalize（）方法中调用？

推荐答案

1. notify 将唤醒一个在监视器上等待的线程。除非直到监视器无主，否则不能运行任何线程;必须在同步块中调用wait（），因此必须保持锁定才能继续运行该块。


2. 无保证。调用 notifyAll 给所有线程偶然唤醒。


3. Dunno。你可以让线程设置一个变量，说它在等待它进入睡眠状态之前等待...


4. 这可能是一个坏主意。你能想出一个必要的情况吗？

1. notify will wake one thread waiting on the monitor. Unless and until the monitor is unowned, no thread waiting can run; wait() must be called in a synchronized block and so the lock must be held to continue running that block.
2. No guarantees. Call notifyAll to give all threads a chance to wake.
3. Dunno. You could have the thread set a variable saying it's waiting before it goes to sleep...
4. This is probably a bad idea. Can you come up with a situation where this is necessary?

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