count down latch using aqs

MyCountDown.java

private final class Sync extends AbstractQueuedSynchronizer {
		private int count;

		public Sync(int count) {
			this.count = count;
		}

		@Override
		protected int tryAcquireShared(int arg) {
			return (getState() == 0 ? 1 : -1);
		}

		@Override
		protected boolean tryReleaseShared(int arg) {
			for (;;) {
				int c = getState();
				if (c == 0) {
					return false;
				}
				int nextc = c - 1;
				if (compareAndSetState(c, nextc)) {
					return nextc == 0;
				}
			}
		}
	}

	private Sync sync = null;

	private int count;
	public MyCountDown(int count) {
		this.sync = new Sync(count);
	}
	public void await() throws InterruptedException {
		sync.acquireSharedInterruptibly(1);
	}

	public void countDown() {
		sync.releaseShared(1);
	}
}