阻塞算法Semaphore实现

public class SemaphoreSynchronousQueue<E> {
E item = null;
Semaphore sync = new Semaphore(0);
Semaphore send = new Semaphore(1);
Semaphore recv = new Semaphore(0);

public E take() throws InterruptedException {
recv.acquire();
E x = item;
sync.release();
send.release();
return x;
}

public void put (E x) throws InterruptedException{
send.acquire();
item = x;
recv.release();
sync.acquire();
}
}