AbstractQueuedSynchronizer（三）——acquireInterruptibly/doAcquireInterruptibly方法

/**     * Acquires in exclusive mode, aborting if interrupted.     * Implemented by first checking interrupt status, then invoking     * at least once {@link #tryAcquire}, returning on     * success.  Otherwise the thread is queued, possibly repeatedly     * blocking and unblocking, invoking {@link #tryAcquire}     * until success or the thread is interrupted.  This method can be     * used to implement method {@link Lock#lockInterruptibly}.     *     * @param arg the acquire argument.  This value is conveyed to     *        {@link #tryAcquire} but is otherwise uninterpreted and     *        can represent anything you like.     * @throws InterruptedException if the current thread is interrupted     */    public final void acquireInterruptibly(int arg)            throws InterruptedException {        if (Thread.interrupted())            throw new InterruptedException();        if (!tryAcquire(arg))            doAcquireInterruptibly(arg);    }

1.原理对比

和acquire的唯一不同，就是在于它能够在外界对当前线程进行中断的时候提前结束获取状态的操作，换句话说，

就是在类似synchronized获取锁时，外界能够对当前线程进行中断，并且获取锁的这个操作能够响应中断并提前返回。
一个线程处于synchronized块中或者进行同步I/O操作时，对该线程进行中断操作，这时该线程的中断标识位被设置为true，
但是线程依旧继续运行。
如果在获取一个通过网络交互实现的锁时，这个锁资源突然进行了销毁，那么使用acquireInterruptibly的获取方式
就能够让该时刻尝试获取锁的线程提前返回。而同步器的这个特性被实现Lock接口中的lockInterruptibly方法。
根据Lock的语义，在被中断时，lockInterruptibly将会抛出InterruptedException来告知使用者。

2.代码对比

{@link java.util.concurrent.locks.AbstractQueuedSynchronizer#acquireQueued}和
{@link java.util.concurrent.locks.AbstractQueuedSynchronizer#doAcquireInterruptibly(int)}，
在判断有interrupt的时候，前者正常执行代码，并返回一个boolean变量，但是后者直接抛出

{@link java.lang.InterruptedException}异常。

if (shouldParkAfterFailedAcquire(p, node) &&                    parkAndCheckInterrupt())                    interrupted = true;

if (shouldParkAfterFailedAcquire(p, node) &&                    parkAndCheckInterrupt())                    throw new InterruptedException();