java并发 - 学习ConditionObject

        /** First node of condition queue. */
        private transient Node firstWaiter;
        /** Last node of condition queue. */
        private transient Node lastWaiter;

        /**
         * Implements interruptible condition wait.
         * 

         * 
 If current thread is interrupted, throw InterruptedException.
         * 
 Save lock state returned by {
@link #getState}.
         * 
 Invoke {@link #release} with saved state as argument,
         *      throwing IllegalMonitorStateException if it fails.
         * 
 Block until signalled or interrupted.
         * 
 Reacquire by invoking specialized version of
         *      {@link #acquire} with saved state as argument.
         * 
 If interrupted while blocked in step 4, throw InterruptedException.
         * 
         */
        public final void await() throws InterruptedException {
            if (Thread.interrupted())   // 检查是否被中断
                throw new InterruptedException(); 
            Node node = addConditionWaiter();  // 将本线程添加进ConditionObject等待队列
            int savedState = fullyRelease(node); // 安全使用本方法必先获得锁, 由于已获得锁, 释放锁
            int interruptMode = 0;
            while (!isOnSyncQueue(node)) { // 如果当前线程不在AQS同步队列中, 则阻塞当前线程
                LockSupport.park(this);
                if ((interruptMode = checkInterruptWhileWaiting(node)) != 0)
                    break;
            }
            if (acquireQueued(node, savedState) && interruptMode != THROW_IE) //如果在AQS同步队列中,则尝试获取锁, 获取失败则阻塞当前线程
                interruptMode = REINTERRUPT;
            if (node.nextWaiter != null) // clean up if cancelled
                unlinkCancelledWaiters();
            if (interruptMode != 0)
                reportInterruptAfterWait(interruptMode);
        }

       /**
         * Moves the longest-waiting thread, if one exists, from the
         * wait queue for this condition to the wait queue for the
         * owning lock.
         *
         * @throws IllegalMonitorStateException if {@link #isHeldExclusively}
         *         returns {@code false}
         */
        public final void signal() {
            if (!isHeldExclusively())
                throw new IllegalMonitorStateException();
            Node first = firstWaiter;
            if (first != null)
                doSignal(first);
        }

        /**
         * Removes and transfers nodes until hit non-cancelled one or
         * null. Split out from signal in part to encourage compilers
         * to inline the case of no waiters.
         * @param first (non-null) the first node on condition queue
         */
        private void doSignal(Node first) {
            do {
                if ( (firstWaiter = first.nextWaiter) == null)
                    lastWaiter = null;
                first.nextWaiter = null;
            } while (!transferForSignal(first) &&    //将在ConditionObject等待队列中的节点转移到AQS同步队列中
                     (first = firstWaiter) != null);
        }

    /**
     * Transfers a node from a condition queue onto sync queue.
     * Returns true if successful.
     * @param node the node
     * @return true if successfully transferred (else the node was
     * cancelled before signal)
     */
    final boolean transferForSignal(Node node) {
        /*
         * If cannot change waitStatus, the node has been cancelled.
         */
        if (!compareAndSetWaitStatus(node, Node.CONDITION, 0))
            return false;

        /*
         * Splice onto queue and try to set waitStatus of predecessor to
         * indicate that thread is (probably) waiting. If cancelled or
         * attempt to set waitStatus fails, wake up to resync (in which
         * case the waitStatus can be transiently and harmlessly wrong).
         */
        Node p = enq(node);  //进入AQS队列
        int ws = p.waitStatus;
        if (ws > 0 || !compareAndSetWaitStatus(p, ws, Node.SIGNAL))
            LockSupport.unpark(node.thread);
        return true;
    }