Synchronising twice on the same object?

Question

I was wondering if in Java I would get any odd behaviour if I synchronise twice on the same object?

The scenario is as follows

pulbic class SillyClas         


        

Answer 1

I think we have to use reentrant lock for what you are trying to do. Here's a snippet from http://docs.oracle.com/javase/1.5.0/docs/api/java/util/concurrent/locks/ReentrantLock.html.

What do we mean by a reentrant lock? Simply that there is an acquisition count associated with the lock, and if a thread that holds the lock acquires it again, the acquisition count is incremented and the lock then needs to be released twice to truly release the lock. This parallels the semantics of synchronized; if a thread enters a synchronized block protected by a monitor that the thread already owns, the thread will be allowed to proceed, and the lock will not be released when the thread exits the second (or subsequent) synchronized block, but only will be released when it exits the first synchronized block it entered protected by that monitor.

Though I have not tried it, I guess if you want to do what you have above, you have to use a re-entrant lock.