Finisher

public final class Latch
{
    private final Object monitor = new Object();

    private int counter = 0;
    private boolean canStart = true;

    public boolean tryStart()
    {
        synchronized (monitor)
        {
            if (canStart)
            {
                counter++;
                return true;
            }

            return false;
        }
    }

    public void finish()
    {
        synchronized (monitor)
        {
            counter--;
            if (0 == counter)
            {
                monitor.notifyAll();
            }
        }
    }

    public void waitForZero() throws InterruptedException
    {
        synchronized (monitor)
        {
            canStart = false;

            while (0 != counter)
            {
                monitor.wait();
            }
        }
    }
}