[POOL-284] "Returned object not currently part of this pool" when using mutable objects

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 2.2
• Fix Version/s: 2.4.1
• Assignee: Unassigned
• Reporter: Valentin Mayamsin
• Created: 27/Jan/15 23:54
• Updated: 01/Jun/15 15:48
• Resolved: 12/May/15 13:33

Description

I'm using pool to reuse expensive Sets (storing millions of items). Here is a test which fails:

        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 );

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