what's the benefit of the code

Question

While reading the source code of ArrayBlockingQueue, I found below code:

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();
    }
}

why not use the code

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();
    }
}

what's the Benefit of the line code :final ReentrantLock lock = this.lock;

@assylias .possible duplicate – fuyou001 Apr 13 '13 at 13:34 — fuyou001, Apr 13 '13 at 13:34

score 0 · Answer 1 · edited May 23 '17 at 12:04

0

This idea was popularized by Doug Lea - I think that the original idea was that the JVM could possibly perform some performance related optimization when there was a final local variable used.

Check out this thread from the OpenJDK thread which discusses this very question

Edit:

A little research threw up these two related questions on stack:

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

Java Lock variable assignment before use. Why?

edited May 23 '17 at 12:04

Community

1
1

answered Apr 13 '13 at 13:35

Sean Landsman

7,033
2
29
33

This is not the best reference - [this other thread](http://cs.oswego.edu/pipermail/concurrency-interest/2011-January/007703.html) is more informative. – assylias Apr 13 '13 at 13:37

what's the benefit of the code

1 Answers1