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From "Mark Thomas (JIRA)" <j...@apache.org>
Subject [jira] Resolved: (POOL-149) A serious concurrent bug can cause resource leak when Pool exhausted and borrowed objects are invalid
Date Wed, 09 Sep 2009 13:12:57 GMT

     [ https://issues.apache.org/jira/browse/POOL-149?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Mark Thomas resolved POOL-149.
------------------------------

    Resolution: Fixed

This is related  to POOL-147 although it highlights a wider problem.

In short, when testing to see if allocate() had assigned an object, checking latch.getPair()==null
was insufficient. It is also necessary to check latch.mayCreate()==false

This has been patched in trunk and will be fixed in 1.5.3

The attached test case now runs without locking up.

> A serious concurrent bug can cause resource leak when Pool exhausted and borrowed objects
are invalid
> -----------------------------------------------------------------------------------------------------
>
>                 Key: POOL-149
>                 URL: https://issues.apache.org/jira/browse/POOL-149
>             Project: Commons Pool
>          Issue Type: Bug
>    Affects Versions: 1.5, 1.5.1, 1.5.2
>            Reporter: shuyang.zhou
>            Priority: Critical
>             Fix For: 1.5.3
>
>         Attachments: BugTest.java
>
>
> This bug will happen when the pool is in exhausted state and the borrowed object are
invalid.
> Let's go through a simple scenario:
> 1)A GenericObjectPool with _maxActive==1, whenExhaustedAction==WHEN_EXHAUSTED_BLOCK
> 2)Two threads using that pool, called thread1 and thread2
> Here is error path:
> 1)thread1 calls pool.borrowObject() to get the object out of the pool
> //now the pool is exhausted
> 2)thread2 calls pool.borrowObject(), adds a new latch to the _allocationQueue, but before
it enters the synchronized block for WHEN_EXHAUSTED_BLOCK(GenericObjectPool line 1099 revision
806215), context-switch happens
> 3)thread1 checks the object from pool, and decides to invalidate it. So it calls pool.invalidateObject(),
which calls allocate(), then calls latch.notify(), but currently no thread is waiting on this
latch.(thread2 has not enter the wait synchronized block yet).
> 4)Then thread2 will wait there for ever.(it just missed the notify)

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