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https://issues.apache.org/jira/browse/HBASE-6651?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13478592#comment-13478592
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Hiroshi Ikeda commented on HBASE-6651:
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bq. Can you explain why calling clear() followed by returnObject() would result
in return value of false ? There is space in SharedMap at this moment, right ?
SharedMap holds a collection of registered objects independent of whether the
objects are pooled or borrowed, and SharedMap.invalidateObject() and
SharedMap.clear() remove the specified object(s) from the collection.
SharedMap.returnObject() always does nothing and returns false if the given
object is not found in the collection. Filling a space of the registered
objects is done by SharedMap.registerObject(), not SharedMap.returnObject().
> 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, HBASE-6651-V2.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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