ConditionObject分析

Lock lock = new ReentrantLock();
    Condition condition = lock.newCondition();//创建和该锁关联的条件锁
    
    public void conditionWait() throws InterruptedException{
        lock.lock();
        try {
            condition.await();
        }finally {
            lock.unlock();
        }
    }
    public void ConditionSignal() throws InterruptedException{
        lock.lock();
        try {
            condition.signal();
        }finally {
            lock.unlock();
        }
    }

        public final void await() throws InterruptedException {
            if (Thread.interrupted())
                throw new InterruptedException();
            Node node = addConditionWaiter();　　//把当前线程的节点加入到等待队列中
            int savedState = fullyRelease(node);　　//由于调用await()方法的线程是已经获取了锁的，所以在加入到等待队列之后，需要去释放锁，并且唤醒后继节点线程
            int interruptMode = 0;
            while (!isOnSyncQueue(node)) {
                LockSupport.park(this);　　//挂起当前线程，当别的线程调用了signal（），并且是当前线程被唤醒的时候才从park()方法返回
                if ((interruptMode = checkInterruptWhileWaiting(node)) != 0)
                    break;
            }
            if (acquireQueued(node, savedState) && interruptMode != THROW_IE) //当被唤醒后，该线程会尝试去获取锁，只有获取到了才会从await()方法返回，否则的话，会挂起自己
                interruptMode = REINTERRUPT;
            if (node.nextWaiter != null) // clean up if cancelled
                unlinkCancelledWaiters();
            if (interruptMode != 0)
                reportInterruptAfterWait(interruptMode);
        }

        private Node addConditionWaiter() {
            Node t = lastWaiter;
            // If lastWaiter is cancelled, clean out.
            if (t != null && t.waitStatus != Node.CONDITION) {　　//首先判断lastWaiter节点是否为空，或者是否是处于条件等待，如果不是的话则把它从等待队列中删除。
                unlinkCancelledWaiters();
                t = lastWaiter;
            }
            Node node = new Node(Thread.currentThread(), Node.CONDITION);
            if (t == null)　　　　　　　　//把当前线程构建的节点加入到等待队列中去，并且返回当前节点
                firstWaiter = node;
            else
                t.nextWaiter = node;
            lastWaiter = node;
            return node;
        }

    final int fullyRelease(Node node) {
        boolean failed = true;
        try {
            int savedState = getState();
            if (release(savedState)) {
                failed = false;
                return savedState;
            } else {
                throw new IllegalMonitorStateException();
            }
        } finally {
            if (failed)
                node.waitStatus = Node.CANCELLED;
        }
    }

        private void doSignal(Node first) {
            do {
                if ( (firstWaiter = first.nextWaiter) == null)
                    lastWaiter = null;
                first.nextWaiter = null;
            } while (!transferForSignal(first) &&　　　　//从first开始遍历等待队列，把第一个非空、没取消的节点transfer到同步队列
                     (first = firstWaiter) != null);
        }

        public final void signal() {
            if (!isHeldExclusively())
                throw new IllegalMonitorStateException();
            Node first = firstWaiter;
            if (first != null)
                doSignal(first);
        }

    /**
     * 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);　　//返回的是node的前一个节点
        int ws = p.waitStatus;
        if (ws > 0 || !compareAndSetWaitStatus(p, ws, Node.SIGNAL))
            LockSupport.unpark(node.thread);　　//唤醒刚加入到同步队列的线程，被唤醒之后，该线程才能从await()方法的park()中返回。
        return true;
    }