关于Java BlockingQueue源码学习的一个问题

Question

先附上BlockingQueue源码take()代码：

public class ArrayBlockingQueue<E> implements BlockingQueue<E> {

    final ReentrantLock lock;

    //构造体中初始化lock
    public ArrayBlockingQueue<E>(){
        //...
    }
    public E take() throws InterruptedException {
        final ReentrantLock lock = this.lock;  //疑惑
        lock.lockInterruptibly();
        try {
            while (count == 0)
                notEmpty.await();
            return dequeue();
        } finally {
            lock.unlock();
        }
    }

}

请问take方法中，第一行final ReentrantLock lock = this.lock，为什么要把全局字段lock先复制到一个局部变量中使用呢？？？直接使用全局final lock不可以吗（eg. this.lock.lockInterruptibly()）？？为什么要多此一举呢？

Answer 1

复制进来可以减少接下来“获取字段”的开销
算是挤性能吧

Answer 2

stackoverflow上有相同问题。

...copying to locals produces the smallest bytecode, and for low-level code it's nice to write code that's a little closer to the machine

太底层了，忽略吧