Guarded Blocks with Join

I need to synchronize over several threads. I don't create th开发者_开发问答e threads, but I do know how many there are. So I wrote this inner guarded block:

private class Guard {
    int waiters = 0;
    boolean wait;
    synchronized void addWaiter() {
        ++waiters;
        wait = true;
        while (wait && waiters != threadNum()) {
            try {
                wait();
            } catch (InterruptedException e) {}
        }
        waiters = 0;
        wait = false;
        notifyAll();
    }
}

This guarded block is executed in a loop. So the problem is that it might get called a second time before all the threads from the first call are released from the wait() loop, which obviously screws up the whole logic of the guard. So I need to have the threads join somehow before they are released from the guard. Is there a design for this? What is the most elegant way of accomplishing it. Keep in mind that the threads are not created by me.

Thanks.

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Sounds like a job for a CountDownLatch. You can set the latch to wait for N count downs. See the Javadoc for examples.