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

    • 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();
        }
    View Code

    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);
            }
        }
    View Code

    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);
        }
    View Code

    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);
            }
        }
    View Code
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  • 原文地址:https://www.cnblogs.com/yifanSJ/p/8942549.html
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