ReentrantLock源码解析3--优先响应中断的lockInterruptibly

合集 - 并发(22)

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17.ReentrantLock源码解析3--优先响应中断的lockInterruptibly2018-04-25

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收起

• ReentrantLock.lockInterruptibly允许在等待时由其它线程调用等待线程的Thread.interrupt方法来中断等待线程的等待而直接返回，这时不用获取锁，而会抛出一个InterruptedException。
• ReentrantLock.lock方法不允许Thread.interrupt中断,即使检测到Thread.isInterrupted,一样会继续尝试获取锁，失败则继续休眠。只是在最后获取锁成功后再把当前线程置为interrupted状态。

具体实现如下：

1.lock

Lock在第一次获取锁失败后会走：

    public final void acquire(int arg) {
        if (!tryAcquire(arg) &&
            acquireQueued(addWaiter(Node.EXCLUSIVE), arg))
            //中断当前线程
            selfInterrupt();
    }

addWaiter封装Node节点插入到队列尾部，acquireQueued负责队列的挂起、出队、是否中断

    final boolean acquireQueued(final Node node, int arg) {
        boolean failed = true;
        try {
            boolean interrupted = false;
            for (;;) {
                final Node p = node.predecessor();
                if (p == head && tryAcquire(arg)) {
                    setHead(node);
                    p.next = null; // help GC
                    failed = false;
                    //在独占锁后，才返回中断标识
                    return interrupted;
                }
                //shouldParkAfterFailedAcquire：判断线程可否安全挂起
                //parkAndCheckInterrupt：挂起线程并返回当时中断标识Thread.interrupted()
                if (shouldParkAfterFailedAcquire(p, node) &&
                    parkAndCheckInterrupt())
                    //当parkAndCheckInterrupt返回中断标识为true时修改interrupted
                    interrupted = true;
            }
        } finally {
            if (failed)
                cancelAcquire(node);
        }
    }

2. lockInterruptibly

lockInterruptibly会直接走下面程序

    public final void acquireInterruptibly(int arg)
            throws InterruptedException {
        if (Thread.interrupted())
            throw new InterruptedException();
        if (!tryAcquire(arg))
            //没有得到独占锁后
            doAcquireInterruptibly(arg);
    }

doAcquireInterruptibly

    private void doAcquireInterruptibly(int arg)
        throws InterruptedException {
        final Node node = addWaiter(Node.EXCLUSIVE);
        boolean failed = true;
        try {
            for (;;) {
                final Node p = node.predecessor();
                if (p == head && tryAcquire(arg)) {
                    setHead(node);
                    p.next = null; // help GC
                    failed = false;
                    //这里没有中断标识
                    //lock和lockInterruptibly区别就是对中断的处理方式 
                    return;
                }
                //shouldParkAfterFailedAcquire：判断线程可否安全挂起
                //parkAndCheckInterrupt：挂起线程并返回当时中断标识Thread.interrupted()
                if (shouldParkAfterFailedAcquire(p, node) &&
                    parkAndCheckInterrupt())
                    //当parkAndCheckInterrupt返回中断标识为true时立即抛出异常中断线程
                    throw new InterruptedException();
            }
        } finally {
            if (failed)
                cancelAcquire(node);
        }
    }