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https://issues.apache.org/jira/browse/HBASE-6651?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13533600#comment-13533600
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Lars Hofhansl commented on HBASE-6651:
--------------------------------------
See my post:
http://hadoop-hbase.blogspot.com/2011/12/long-running-hbase-clients.html
It's only needed because the API is not designed right. Resources can't be
controlled with it (max is per table). And - without your patch - it didn't
even work correctly.
0.96 is the singularity where we can break stuff, if we do not do it now, we're
stuck with it.
> Improve thread safety of HTablePool
> -----------------------------------
>
> Key: HBASE-6651
> URL: https://issues.apache.org/jira/browse/HBASE-6651
> Project: HBase
> Issue Type: Bug
> Components: Client
> Affects Versions: 0.94.1
> Reporter: Hiroshi Ikeda
> Assignee: Hiroshi Ikeda
> Fix For: 0.96.0
>
> Attachments: HBASE-6651.patch, HBASE-6651-V10.patch,
> HBASE-6651-V2.patch, HBASE-6651-V3.patch, HBASE-6651-V4.patch,
> HBASE-6651-V5.patch, HBASE-6651-V6.patch, HBASE-6651-V7.patch,
> HBASE-6651-V8.patch, HBASE-6651-V9.patch, sample.zip, sample.zip,
> sharedmap_for_hbaseclient.zip
>
>
> There are some operations in HTablePool accessing PoolMap in multiple places
> without any explicit synchronization.
> For example HTablePool.closeTablePool() calls PoolMap.values(), and calls
> PoolMap.remove(). If other threads add new instances to the pool in the
> middle of the calls, the newly added instances might be dropped.
> (HTablePool.closeTablePool() also has another problem that calling it by
> multiple threads causes accessing HTable by multiple threads.)
> Moreover, PoolMap is not thread safe for the same reason.
> For example PoolMap.put() calles ConcurrentMap.get() and calles
> ConcurrentMap.put(). If other threads add a new instance to the concurent map
> in the middle of the calls, the new instance might be dropped.
> And also implementations of Pool have the same problems.
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