Question

在阅读ArrayBlockingQueue的源代码时，我在下面找到了代码：

public E take() throws InterruptedException {
    final ReentrantLock lock = this.lock;
    lock.lockInterruptibly();
    try {
        try {
            while (count == 0)
                notEmpty.await();
        } catch (InterruptedException ie) {
            notEmpty.signal(); // propagate to non-interrupted thread
            throw ie;
        }
        E x = extract();
        return x;
    } finally {
        lock.unlock();
    }
}

为什么不使用代码

public E take() throws InterruptedException {
     lock.lockInterruptibly();
    try {
        try {
            while (count == 0)
                notEmpty.await();
        } catch (InterruptedException ie) {
            notEmpty.signal(); // propagate to non-interrupted thread
            throw ie;
        }
        E x = extract();
        return x;
    } finally {
        lock.unlock();
    }
}

行代码的好处是什么：最终的ReentrantLock lock = this.lock;

Answer 1

这个想法由Doug Lea推广 - 我认为最初的想法是当使用最终的局部变量时，JVM可能会执行一些与性能相关的优化。

从OpenJDK线程中查看this线程，讨论这个问题

编辑：

一些研究在堆栈上提出了这两个相关的问题：

In ArrayBlockingQueue, why copy final member field into local final variable?

Java Lock variable assignment before use. Why?

什么是代码的好处

1 个答案: