Java threads: wait and notify methods

Question

I have a thread that calls the wait method and can only be awoken when the notify method called from some other class:

 class Threa         


        

Answer 1

It is possible for ThreadB's run method to complete before you enter the synchronized block in ThreadA.main. In that situation, since the notify call has happened before you started waiting, ThreadA will block forever on the wait call.

A simple workaround would be to grab the lock on b in main before you start the second thread to ensure the wait happens first.

ThreadB b = new ThreadB();
synchronized(b) {
    b.start();
    ...
    b.wait();
}