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https://issues.apache.org/jira/browse/HIVE-23841?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Adrian Nistor updated HIVE-23841:
---------------------------------
Flags: Patch
> Field writers is an HashSet, i.e., not thread-safe. Field writers is
> typically protected by synchronization on lock, but not in 1 location.
> --------------------------------------------------------------------------------------------------------------------------------------------
>
> Key: HIVE-23841
> URL: https://issues.apache.org/jira/browse/HIVE-23841
> Project: Hive
> Issue Type: Bug
> Environment: Any environment
> Reporter: Adrian Nistor
> Priority: Major
> Attachments: HIVE-23841.patch
>
>
> Field {{writers}} is a {{HashSet}} ([line
> 70|https://github.com/apache/hive/blob/c93d7797329103d6c509bada68b6da7f907b3dee/ql/src/java/org/apache/hadoop/hive/llap/LlapOutputFormatService.java#L70]),
> i.e., not thread-safe.
> Accesses to field {{writers}} are protected by synchronization on {{lock}},
> e.g., at lines:
> [141-144|https://github.com/apache/hive/blob/c93d7797329103d6c509bada68b6da7f907b3dee/ql/src/java/org/apache/hadoop/hive/llap/LlapOutputFormatService.java#L141-L144],
>
> [212-213|https://github.com/apache/hive/blob/c93d7797329103d6c509bada68b6da7f907b3dee/ql/src/java/org/apache/hadoop/hive/llap/LlapOutputFormatService.java#L212-L213],
> and
> [212-215|https://github.com/apache/hive/blob/c93d7797329103d6c509bada68b6da7f907b3dee/ql/src/java/org/apache/hadoop/hive/llap/LlapOutputFormatService.java#L212-L215].
> However, the {{writers.remove()}} at [line
> 249|https://github.com/apache/hive/blob/c93d7797329103d6c509bada68b6da7f907b3dee/ql/src/java/org/apache/hadoop/hive/llap/LlapOutputFormatService.java#L249]
> is protected by synchronization on {{INSTANCE}}, *not* on {{lock}}.
> Synchronizing on 2 different objects does not ensure mutual exclusion. This
> is because 2 threads synchronizing on different objects can still execute in
> parallel at the same time.
> Note that lines
> [215|https://github.com/apache/hive/blob/c93d7797329103d6c509bada68b6da7f907b3dee/ql/src/java/org/apache/hadoop/hive/llap/LlapOutputFormatService.java#L215]
> and
> [249|https://github.com/apache/hive/blob/master/ql/src/java/org/apache/hadoop/hive/llap/LlapOutputFormatService.java#L249]
> are modifying {{writers}} with {{put()}} and {{remove()}}, respectively.
> h1. The Code for This Fix
> This fix is very simple: just change {{synchronized (INSTANCE)}} to
> {{synchronized (lock)}}, just like the methods containing the other lines
> listed above.
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