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Posted to common-issues@hadoop.apache.org by "Steve Loughran (JIRA)" <ji...@apache.org> on 2015/12/01 11:00:18 UTC
[jira] [Commented] (HADOOP-12593) multiple "volatile long" field
declarations exist in the Hadoop codebase
[ https://issues.apache.org/jira/browse/HADOOP-12593?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15033446#comment-15033446 ]
Steve Loughran commented on HADOOP-12593:
-----------------------------------------
I knew some were tagged, and others not. I think my main concern was whether writes to a 64 bit value were atomic at all —but roman corrected me there. Which leaves the issue of: are there any operations which cause problems, with ++, += and the equivalents being it.
I think we should just review them, and for all that we deem safe, add that in big comments.
Life would be easier if java had an {{atomic}} type alongside {{volatile}}, atomic add/subtract operations are only a couple of cycles on a modern part, plus the same impact on OoO scheduling that volatile r/w ops have.
> multiple "volatile long" field declarations exist in the Hadoop codebase
> ------------------------------------------------------------------------
>
> Key: HADOOP-12593
> URL: https://issues.apache.org/jira/browse/HADOOP-12593
> Project: Hadoop Common
> Issue Type: Bug
> Affects Versions: 2.8.0
> Reporter: Steve Loughran
> Priority: Minor
>
> If you get your IDE to scan for "volatile long", you find 20-30 entries. Volatile operations on `long` variables are not guaranteed to be atomic, so these usages can be vulnerable to race conditions generating invalid data.
> they need to be replaced by AtomicLong references, except in the specific case that you want performance values for statistics, and are prepared to take the risk
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