在ArrayBlockingQueue中,为什么要将最终成员字段复制到本地最终变量中? [英] In ArrayBlockingQueue, why copy final member field into local final variable?
问题描述
在 ArrayBlockingQueue
中,所有需要锁定的方法在调用<$之前将其复制到本地 final
变量c $ c> lock()。
In ArrayBlockingQueue
, all the methods that require the lock copy it to a local final
variable before calling lock()
.
public boolean offer(E e) {
if (e == null) throw new NullPointerException();
final ReentrantLock lock = this.lock;
lock.lock();
try {
if (count == items.length)
return false;
else {
insert(e);
return true;
}
} finally {
lock.unlock();
}
}
有没有理由复制 this.lock
到一个局部变量 lock
当字段 this.lock
是 final
?
Is there any reason to copy this.lock
to a local variable lock
when the field this.lock
is final
?
此外,它还使用 E [] $的本地副本c $ c>在采取行动之前:
Additionally, it also uses a local copy of E[]
before acting on it:
private E extract() {
final E[] items = this.items;
E x = items[takeIndex];
items[takeIndex] = null;
takeIndex = inc(takeIndex);
--count;
notFull.signal();
return x;
}
是否有任何理由将最终字段复制到本地最终字段变量?
推荐答案
这是一个极端优化,该课程的作者Doug Lea喜欢使用。这是关于最近的一个主题的帖子在core-libs-dev邮件列表中关于这个确切的主题,很好地回答了你的问题。
It's an extreme optimization Doug Lea, the author of the class, likes to use. Here's a post on a recent thread on the core-libs-dev mailing list about this exact subject which answers your question pretty well.
来自帖子:
...复制到本地生成最小的
字节码,对于低级代码,编写更接近机器的代码
很好
...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
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