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https://issues.apache.org/jira/browse/HADOOP-12593?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15024861#comment-15024861
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Sangjin Lee commented on HADOOP-12593:
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Writes and reads of volatile longs or doubles are very much atomic:
http://docs.oracle.com/javase/specs/jls/se7/html/jls-17.html#jls-17.7
> 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: Critical
>
> 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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