Premature starvation in GenericObjectPool when borrowObject() and evict() are executed concurrently

Hi,

I am encountering a deadlock in GenericObjectPool. It appears in version 1.5.5
and also in revision 1079385 (March 8th 2011).

The deadlock manifests when calling borrowObject() and evict() in parallel. I
have inlined a test that exposes this problem. For this test, the expected
output is:

Expected output:
0
1
2
3
4
.....
498
499
DONE

But when the bug manifests (almost always for this test), the output is:

Bug output:
0
1
2
3
4

When the bug manifests, the test does not finish, it just gets stuck after
printing several values (in this run: 0 1 2 3 4, but in other runs may be
0 1 2 .. 18 or 0 1 2 or some other value).

When the loop limit is small (e.g., 11 instead of 5000), the test does finish.

Also, when running sequentially:

Pool.borrowObject();
Pool.evict();

or vice-versa

Pool.evict();
Pool.borrowObject();

the test still finishes.

Is this a bug? Is there a patch for it?

Thanks!

Adrian

================================================================================
This test is for version 1.5.5. For revision 1079385 one should replace
setMaxActive() with setMaxTotal()
================================================================================
package org.apache.commons.pool.impl;

import org.apache.commons.pool.PoolableObjectFactory;

public class Test01
{
public static void main(String[] args) throws Exception

{ Test01 test = new Test01(); test.test(); }

SimpleFactory Factory = null;
GenericObjectPool Pool = null;
Object Obj = null;
public void test() throws Exception
{
Factory = new SimpleFactory();
Pool = new GenericObjectPool(Factory);
Pool.setMaxActive(1);
Pool.addObject();

for(int i=0; i<5000; i++)
{
Thread one = new MyThread(1);
Thread two = new MyThread(2);
one.start();
two.start();
one.join();
two.join();

Pool.returnObject(Obj);
if(i%10==0)

{ System.out.println(i/10); }

}
System.out.println("DONE");
}

private class MyThread extends Thread
{
int _tid;
public MyThread(int tid)

{ _tid = tid; }

public void run()
{
try
{
if(_tid == 1)

{ Obj = Pool.borrowObject(); }

if (_tid == 2)
{
try

{ Pool.evict(); }

catch (Exception e) {}
}
}
catch(Exception e)

{ throw new RuntimeException(e); }

}
}

private class SimpleFactory implements PoolableObjectFactory
{
public SimpleFactory() {}
public Object makeObject()

{ return new String("testing"); }

public void destroyObject(Object obj) {}
public boolean validateObject(Object obj)

{return true;}
public void activateObject(Object obj) throws Exception {}
public void passivateObject(Object obj) throws Exception {}
public boolean isThrowExceptionOnActivate() {return true;}

}
}
================================================================================