聊聊canal的BooleanMutex

public class BooleanMutex {
​
    private Sync sync;
​
    public BooleanMutex(){
        sync = new Sync();
        set(false);
    }
​
    public BooleanMutex(Boolean mutex){
        sync = new Sync();
        set(mutex);
    }
​
    /**
     * 阻塞等待Boolean为true
     * 
     * @throws InterruptedException
     */
    public void get() throws InterruptedException {
        sync.innerGet();
    }
​
    /**
     * 阻塞等待Boolean为true,允许设置超时时间
     * 
     * @param timeout
     * @param unit
     * @throws InterruptedException
     * @throws TimeoutException
     */
    public void get(long timeout, TimeUnit unit) throws InterruptedException, TimeoutException {
        sync.innerGet(unit.toNanos(timeout));
    }
​
    /**
     * 重新设置对应的Boolean mutex
     * 
     * @param mutex
     */
    public void set(Boolean mutex) {
        if (mutex) {
            sync.innerSetTrue();
        } else {
            sync.innerSetFalse();
        }
    }
​
    public boolean state() {
        return sync.innerState();
    }
​
    //......
}

    private final class Sync extends AbstractQueuedSynchronizer {
​
        private static final long serialVersionUID = 2559471934544126329L;
        /** State value representing that TRUE */
        private static final int  TRUE             = 1;
        /** State value representing that FALSE */
        private static final int  FALSE            = 2;
​
        private boolean isTrue(int state) {
            return (state & TRUE) != 0;
        }
​
        /**
         * 实现AQS的接口，获取共享锁的判断
         */
        protected int tryAcquireShared(int state) {
            // 如果为true，直接允许获取锁对象
            // 如果为false，进入阻塞队列，等待被唤醒
            return isTrue(getState()) ? 1 : -1;
        }
​
        /**
         * 实现AQS的接口，释放共享锁的判断
         */
        protected boolean tryReleaseShared(int ignore) {
            // 始终返回true，代表可以release
            return true;
        }
​
        boolean innerState() {
            return isTrue(getState());
        }
​
        void innerGet() throws InterruptedException {
            acquireSharedInterruptibly(0);
        }
​
        void innerGet(long nanosTimeout) throws InterruptedException, TimeoutException {
            if (!tryAcquireSharedNanos(0, nanosTimeout)) throw new TimeoutException();
        }
​
        void innerSetTrue() {
            for (;;) {
                int s = getState();
                if (s == TRUE) {
                    return; // 直接退出
                }
                if (compareAndSetState(s, TRUE)) {// cas更新状态，避免并发更新true操作
                    releaseShared(0);// 释放一下锁对象，唤醒一下阻塞的Thread
                    return;
                }
            }
        }
​
        void innerSetFalse() {
            for (;;) {
                int s = getState();
                if (s == FALSE) {
                    return; // 直接退出
                }
                if (compareAndSetState(s, FALSE)) {// cas更新状态，避免并发更新false操作
                    return;
                }
            }
        }
​
    }