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From "shuyang.zhou (JIRA)" <j...@apache.org>
Subject [jira] Created: (POOL-149) A serious concurrent bug can cause deadlock when Pool exhausted and borrowed objects are invalid
Date Thu, 20 Aug 2009 16:34:14 GMT
A serious concurrent bug can cause deadlock when Pool exhausted and borrowed objects are invalid
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                 Key: POOL-149
                 URL: https://issues.apache.org/jira/browse/POOL-149
             Project: Commons Pool
          Issue Type: Bug
            Reporter: shuyang.zhou
            Priority: Critical


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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