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https://issues.apache.org/jira/browse/HADOOP-7183?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13021625#comment-13021625
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Owen O'Malley commented on HADOOP-7183:
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The test needs to be removed from the fix, since it is only testing the
implementation detail of this workaround fix.
Tests need to reflect the correct semantics of the code, not implementation
details that will be removed when someone has time to do the right fix.
> WritableComparator.get should not cache comparator objects
> ----------------------------------------------------------
>
> Key: HADOOP-7183
> URL: https://issues.apache.org/jira/browse/HADOOP-7183
> Project: Hadoop Common
> Issue Type: Bug
> Affects Versions: 0.22.0
> Reporter: Todd Lipcon
> Assignee: Tom White
> Priority: Blocker
> Fix For: 0.20.3, 0.21.1, 0.22.0
>
> Attachments: HADOOP-7183.patch
>
>
> HADOOP-6881 modified WritableComparator.get such that the constructed
> WritableComparator gets saved back into the static map. This is fine for
> stateless comparators, but some comparators have per-instance state, and thus
> this becomes thread-unsafe and causes errors in the shuffle where multiple
> threads are doing comparisons. An example of a Comparator with per-instance
> state is WritableComparator itself.
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