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From "Sebb (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (POOL-284) "Returned object not currently part of this pool" when using mutable objects
Date Mon, 02 Feb 2015 17:07:35 GMT

    [ https://issues.apache.org/jira/browse/POOL-284?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14301465#comment-14301465
] 

Sebb commented on POOL-284:
---------------------------

I'm not sure if this matters here, but note that System.identityHashCode does not guarantee
distinct hashes for different objects.
There may be multiple objects with the same hash (but obviously only one hash for a given
object).

> "Returned object not currently part of this pool" when using mutable objects
> ----------------------------------------------------------------------------
>
>                 Key: POOL-284
>                 URL: https://issues.apache.org/jira/browse/POOL-284
>             Project: Commons Pool
>          Issue Type: Bug
>    Affects Versions: 2.2
>            Reporter: Valentin Mayamsin
>
> I'm using pool to reuse expensive Sets (storing millions of items). Here is a test which
fails:
> {code}
>         GenericObjectPoolConfig config = new GenericObjectPoolConfig ();
>         GenericObjectPool<Set> aPool = new GenericObjectPool<> ( new BasePooledObjectFactory<Set>
()
>         {
>             @Override
>             public Set create () throws Exception
>             {
>                 return new HashSet();
>             }
>             @Override
>             public PooledObject<Set> wrap ( Set o )
>             {
>                 return new DefaultPooledObject<> ( o );
>             }
>             @Override
>             public void passivateObject ( PooledObject<Set> p ) throws Exception
>             {
>                 p.getObject ().clear ();
>                 super.passivateObject ( p );
>             }
>         }, config );
>         Set set = aPool.borrowObject ();
>         set.add ( new Object () );
>         
>         aPool.returnObject ( set );
> {code}
> This is because GenericObjectPool uses a HashMap<Object, PooledObject> to correlate
objects and state. HashMap stores objects correlated to their hashCode. So in case object's
state change then hashCode will change, thus Map will fail to correlate this object since
it stores old hashCode



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