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https://issues.apache.org/jira/browse/ZOOKEEPER-955?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12969365#action_12969365
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Thomas Koch commented on ZOOKEEPER-955:
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I'm myself +0 on this patch after what I've learned about synchronization now.
It was just a WTF moment when I saw this code and asked myself why the author
didn't use Atomic classes from the beginning. The comment you mentioned ("This
should be called from a synchronized block on this!") is obsolete, I believe
since the function is already synchronized.
> Use Atomic(Integer|Long) for (Z)Xid
> -----------------------------------
>
> Key: ZOOKEEPER-955
> URL: https://issues.apache.org/jira/browse/ZOOKEEPER-955
> Project: ZooKeeper
> Issue Type: Improvement
> Components: java client, server
> Reporter: Thomas Koch
> Assignee: Thomas Koch
> Priority: Trivial
> Attachments: ZOOKEEPER-955.patch
>
>
> As I've read last weekend in the fantastic book "Clean Code", it'd be much
> faster to use AtomicInteger or AtomicLong instead of synchronization blocks
> around each access to an int or long.
> The key difference is, that a synchronization block will in any case acquire
> and release a lock. The atomic classes use "optimistic locking", a CPU
> operation that only changes a value if it still has not changed since the
> last read.
> In most cases the value has not changed since the last visit so the operation
> is just as fast as a normal operation. If it had changed, then we read again
> and try to change again.
> [1] Clean Code: A Handbook of Agile Software Craftsmanship (Robert C. Martin)
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