calling Thread.sleep() from synchronized context in Java

问题

I have read that Thread.sleep() will pause the currently running thread for the time specified after which it goes back to runnable state waiting for it's turn to run.

Also, if called from synchronized context, sleep() doesn't release the lock it holds. So I was wondering when it will release the lock. If the thread, put on sleep, never gets the chance to run so it will always keep the lock with itself and then how other threads get to enter synchronized methods/block.

I am not sure if I am asking valid question. But please help me out.

回答1:

So I was wondering when it will release the lock.

It will release the lock upon exit from the synchronized block, and not earlier.

If the thread, put on sleep, never gets the chance to run so it will always keep the lock with itself and then how other threads get to enter synchronized methods/block.

Quite simply, other threads will not be able to enter code that's synchronized on the same object that the sleeping thread.

To summarize, calling Thread.sleep() from a synchronized block is likely not a good idea.

回答2:

If you use Object.wait instead of Thread.sleep, the lock from the synchronized block will be released.

来源：https://stackoverflow.com/questions/10663920/calling-thread-sleep-from-synchronized-context-in-java