代码有什么好处[重复]

Question

在阅读 ArrayBlockingQueue 的源代码时，我发现以下代码：

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();
    }
}

行代码有什么好处：final ReentrantLock lock = this.lock;

Answer 1

Doug Lea 推广了这个想法——我认为最初的想法是当使用 final 局部变量时，JVM 可能会执行一些与性能相关的优化。

从讨论这个问题的 OpenJDK 线程中查看 this 线程

编辑：

一点研究在堆栈上抛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?