高并发场景下一种比读写锁更快的锁，看完我彻底折服了 - 今日头条

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public class StampedLockDemo{
    //创建StampedLock锁对象
    public StampedLock stampedLock = new StampedLock();
    
    //获取、释放读锁
    public void testGetAndReleaseReadLock(){
        long stamp = stampedLock.readLock();
        try{
            //执行获取读锁后的业务逻辑
        }finally{
            //释放锁
            stampedLock.unlockRead(stamp);
        }
    }
    
    //获取、释放写锁
    public void testGetAndReleaseWriteLock(){
        long stamp = stampedLock.writeLock();
        try{
            //执行获取写锁后的业务逻辑。
        }finally{
            //释放锁
            stampedLock.unlockWrite(stamp);
        }
    }
}

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class Point {
    private double x, y;
    private final StampedLock sl = new StampedLock();

    void move(double deltaX, double deltaY) { // an exclusively locked method
        long stamp = sl.writeLock();
        try {
            x += deltaX;
            y += deltaY;
        } finally {
            sl.unlockWrite(stamp);
        }
    }

    double distanceFromOrigin() { // A read-only method
        long stamp = sl.tryOptimisticRead();
        double currentX = x, currentY = y;
        if (!sl.validate(stamp)) {
            stamp = sl.readLock();
            try {
                currentX = x;
                currentY = y;
            } finally {
                sl.unlockRead(stamp);
            }
        }
        return Math.sqrt(currentX * currentX + currentY * currentY);
    }

    void moveIfAtOrigin(double newX, double newY) { // upgrade
        // Could instead start with optimistic, not read mode
        long stamp = sl.readLock();
        try {
            while (x == 0.0 && y == 0.0) {
                long ws = sl.tryConvertToWriteLock(stamp);
                if (ws != 0L) {
                    stamp = ws;
                    x = newX;
                    y = newY;
                    break;
                }
                else {
                    sl.unlockRead(stamp);
                    stamp = sl.writeLock();
                }
            }
        } finally {
            sl.unlock(stamp);
        }
    }
}

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double distanceFromOrigin() { // A read-only method
    //乐观读
    long stamp = sl.tryOptimisticRead();
    double currentX = x, currentY = y;
    //判断是否有线程对变量进行了写操作
    //如果有线程对共享变量进行了写操作
    //则sl.validate(stamp)会返回false
    if (!sl.validate(stamp)) {
        //将乐观读升级为悲观读锁
        stamp = sl.readLock();
        try {
            currentX = x;
            currentY = y;
        } finally {
            //释放悲观锁
            sl.unlockRead(stamp);
        }
    }
    return Math.sqrt(currentX * currentX + currentY * currentY);
}

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while (pred.locked) {
    //省略操作 
}

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public void testStampedLock() throws Exception{
    final StampedLock lock = new StampedLock();
    Thread thread01 = new Thread(()->{
        // 获取写锁
        lock.writeLock();
        // 永远阻塞在此处，不释放写锁
        LockSupport.park();
    });
    thread01.start();
    // 保证thread01获取写锁
    Thread.sleep(100);
    Thread thread02 = new Thread(()->
                           //阻塞在悲观读锁
                           lock.readLock()
                          );
    thread02.start();
    // 保证T2阻塞在读锁
    Thread.sleep(100);
    //中断线程thread02
    //会导致线程thread02所在CPU飙升
    thread02.interrupt();
    thread02.join();
}