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https://issues.apache.org/jira/browse/HADOOP-12412?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14746228#comment-14746228
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Ravi Prakash commented on HADOOP-12412:
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Hi Michael! Thanks a lot for your contribution. Please read through
https://wiki.apache.org/hadoop/HowToContribute . Would you please be able to
write unit tests to demonstrate problems in the existing code, and to prove
that your patch fixes them?
> Concurrency in FileSystem$Cache is very broken
> ----------------------------------------------
>
> Key: HADOOP-12412
> URL: https://issues.apache.org/jira/browse/HADOOP-12412
> Project: Hadoop Common
> Issue Type: Bug
> Components: fs
> Affects Versions: 2.7.0
> Reporter: Michael Harris
> Assignee: Michael Harris
> Priority: Critical
> Attachments: HADOOP-12412.patch
>
>
> The FileSystem cache uses a mild amount of concurrency to protect the cache
> itself, but does nothing to prevent multiple of the same filesystem from
> being constructed and initialized simultaneously. At best, this leads to
> potentially expensive wasted work. At worst, as is the case for Spark, it
> can lead to deadlocks/livelocks, especially when the same configuration
> object is passed into both calls. This should be refactored to use a results
> cache approach (reference Java Concurrency in Practice chapter 5 section 6
> for an example of how to do this correctly), which will be both
> higher-performance and safer.
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