源码

semaphore.acquire()

    public void acquire() throws InterruptedException {
        sync.acquireSharedInterruptibly(1);
    }

    public final void acquireSharedInterruptibly(int arg)
            throws InterruptedException {
        if (Thread.interrupted())
            throw new InterruptedException();
        if (tryAcquireShared(arg) < 0)
            //AQS 的排队过程
            doAcquireSharedInterruptibly(arg);
    }

        protected int tryAcquireShared(int acquires) {
            for (;;) {
                if (hasQueuedPredecessors())
                    return -1;
                int available = getState();
                int remaining = available - acquires;
                // 小于0 或者 CAS成功  ，如果小于0会短路，不执行cas操作
                if (remaining < 0 || compareAndSetState(available, remaining))
                    return remaining;
            }
        }