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From "Hiroshi Ikeda (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-6651) Thread safety of HTablePool is doubtful
Date Wed, 05 Sep 2012 14:22:07 GMT

    [ https://issues.apache.org/jira/browse/HBASE-6651?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13448770#comment-13448770

Hiroshi Ikeda commented on HBASE-6651:

* I think ThreadLocalPool is useless and dangerous. You never access a content in ThreadLocal
from other threads, and if you require information in the content to dispose its container
object or something, you must collect the information by using all the thread that you ever
used to access.

* RoundRobinPool might give the same object to different threads.

* It is bad to use conccurent collections. We should explictly lock larger sections to keep
consistency, or remove synchronization concerns from PoolMap with using explicit locks from
outside of PoolMap.

* PoolMap breaks the contract of Map; The actual behaviors of the methods of PoolMap are vague.
Also filling out the methods of Map causes the code dirty. We should simplify the code by
removing the needless implementation at the start.

> 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
> 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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