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From "Thomas Neidhart (JIRA)" <>
Subject [jira] [Updated] (POOL-287) GKOP can lose objects over time due to swallowed NPE in the evictor
Date Sat, 21 Feb 2015 19:49:11 GMT


Thomas Neidhart updated POOL-287:
    Attachment: POOL-287-fix.patch

Difficult to catch, but great that you did come up with a test case.
I think the idea with an iterator that holds a reference to its idleObject deque is fine,
see the attached patch for a possible implementation.

> GKOP can lose objects over time due to swallowed NPE in the evictor
> -------------------------------------------------------------------
>                 Key: POOL-287
>                 URL:
>             Project: Commons Pool
>          Issue Type: Bug
>    Affects Versions: 2.0, 2.1, 2.2, 2.3
>            Reporter: Caleb Spare
>             Fix For: 2.4
>         Attachments: POOL-287-fix.patch, POOL-287-test.patch
> 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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