锁的优化及注意事项(读书笔记)

/** Lock held by take, poll, etc */
private final ReentrantLock takeLock = new ReentrantLock();//take锁

/** Wait queue for waiting takes */
private final Condition notEmpty = takeLock.newCondition();//生成一个take锁的绑定Condition实例

/** Lock held by put, offer, etc */
private final ReentrantLock putLock = new ReentrantLock();//put锁

/** Wait queue for waiting puts */
private final Condition notFull = putLock.newCondition();//put锁

public E take() throws InterruptedException {
    E x;
    int c = -1;
    final AtomicInteger count = this.count;
    final ReentrantLock takeLock = this.takeLock;
    takeLock.lockInterruptibly();//加锁,可以响应中断的锁
    try {
        while (count.get() == 0) {//如果没有数据,一直等待
            notEmpty.await();//等待put()操作的通知
        }
        x = dequeue();//取得第一个数据
        c = count.getAndDecrement();//数量减1,原子操作,因为会和put()函数同时访问count.注意:变量c是count减1前的值
        if (c > 1)
            notEmpty.signal();//通知其他take操作
    } finally {
        takeLock.unlock();//释放锁
    }
    if (c == capacity)
        signalNotFull();//通知put()操作,已有空余空间
    return x;
}

public void put(E e) throws InterruptedException {
    if (e == null) throw new NullPointerException();
    // Note: convention in all put/take/etc is to preset local var
    // holding count negative to indicate failure unless set.
    int c = -1;
    Node<E> node = new Node<E>(e);
    final ReentrantLock putLock = this.putLock;
    final AtomicInteger count = this.count;
    putLock.lockInterruptibly();//加锁,可以相应中断的锁
    try {
        /*
         * Note that count is used in wait guard even though it is
         * not protected by lock. This works because count can
         * only decrease at this point (all other puts are shut
         * out by lock), and we (or some other waiting put) are
         * signalled if it ever changes from capacity. Similarly
         * for all other uses of count in other wait guards.
         */
        while (count.get() == capacity) {//当数据满了时候
            notFull.await();//等待
        }
        enqueue(node);//插入数据
        c = count.getAndIncrement();//更新数据,变量c是count加1前的值
        if (c + 1 < capacity)
            notFull.signal();//有足够空间,通知其他线程
    } finally {
        putLock.unlock();//释放锁
    }
    if (c == 0)
        signalNotEmpty();//插入成功后,通知take操作取数据
}