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