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From "Hiroshi Ikeda (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (HBASE-6651) Thread safety of HTablePool is doubtful
Date Thu, 11 Oct 2012 09:13:11 GMT

     [ https://issues.apache.org/jira/browse/HBASE-6651?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel

Hiroshi Ikeda updated HBASE-6651:

    Attachment: HBASE-6651.patch

Added a patch.

Added a new interface SharedMap, and added its implementations and unit tests, and made HBaseClient
and HTablePool use SharedMap instead of PoolMap. The API of HTablePool is marked as “stable”
and some constructors of HTablePool uses a static nested class PoolMap.PoolType, and I’m
not sure how to add Deprecated marker partially to PoolMap, so I did nothing about it.

I don’t have environment to run the whole test of HBase, and except tests added for SharedMap
I only confirm that Eclipse can compile the patched code (where the projects are imported
as “existing maven projects” from the trunk). I hope it will work well.

I purged ThreadLocal base logic from HBaseClient (that logic is terrible and I never believe
that works well). Instead, I complicate the Round-Robin based logic to prefer to give idle
connections to requesters. I think, this is the same reason why the ThreadLocal based logic
makes high performance. Moreover, in order to find idle objects in the pool, SharedMap has
different methods from PoolMap, and I rewrote and fixed many parts of HBaseClient. On the
other hand fixing HTablePool to SharedMap is straightforward and I think I have no additional
explanations about it.

> Thread safety of HTablePool is doubtful
> ---------------------------------------
>                 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
>            Priority: Minor
>         Attachments: HBASE-6651.patch, sample.zip, sample.zip, sharedmap_for_hbaseclient.zip
> There are some operations in HTablePool to access to PoolMap in multiple times without
any explict synchronization. 
> For example HTablePool.closeTablePool() calles PoolMap.values(), and calles PoolMap.remove().
If other threads add new instances to the pool in the middle of the calls, the new added instances
might be dropped. (HTablePool.closeTablePool() also has another problem that calling it by
multple 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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