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https://issues.apache.org/jira/browse/POOL-287?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14320052#comment-14320052
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Phil Steitz commented on POOL-287:
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Thanks for the report and code analysis, which looks correct to me. We should
be able to develop a test case for this. Patches welcome, of course, but no
need to attach the Clojure program.
> GKOP can lose objects over time due to swallowed NPE in the evictor
> -------------------------------------------------------------------
>
> Key: POOL-287
> URL: https://issues.apache.org/jira/browse/POOL-287
> Project: Commons Pool
> Issue Type: Bug
> Affects Versions: 2.2, 2.3
> Reporter: Caleb Spare
>
> We ran into this bug via a Redis library that uses a GenericKeyedObjectPool
> for connection pooling. We found that over the course of several days, the
> connections available to our application were dwindling.
> Some relevant configuration:
> testWhileIdle: false
> numTestsPerEvictionRun: -1
> minEvictableIdleTimeMillis: 60000
> timeBetweenEvictionRunsMillis: 30000
> maxTotalPerKey 400
> maxIdlePerKey 400
> (In a more minimal repro case I developed later, the problem happens much
> faster if minEvictableIdleTimeMillis and timeBetweenEvictionRunsMillis are
> reduced greatly, even down to 1.)
> We discovered that this is what happens (looking at 2.3 code, but the problem
> occurred with 2.2 and 2.3):
> * In evict(), there is a variable idleObjects which starts as null
> * The branch where idleObjects is set is not necessarily taken
> * The null idleObjects is passed to underTest.endEvictionTest(idleObjects)
> * If the object underTest had previously been borrowed and was thus set to
> the EVICTION_RETURN_TO_HEAD state, then endEvictionTest throws a NPE
> * By default this is silently swallowed and the evictor continues on
> * Now the object that had been underTest is set to state IDLE, but is not in
> the pool's idleObjects list, so it is lost
> If it would help, I can clean up my repro program and attach that, but it is
> written in Clojure, not Java. I can also try to write a Java repro but I
> might not have time to do that for a little while.
> This bug can be avoided by disabling the evictor. That doesn't help us,
> though, because we rely on background eviction to avoid running into
> server-side connection timeouts.
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