[pool] Validation code invoked on unexpected timing.

[Noriyuki Torii]

Hi, all.

I found BasePooledObjectFactory.validateObject() of commons-pool
sometimes called
on unexpected timing and I cannot identify the cause.
So I would like to ask some advice.

I've configured the pool so as to the validateObject() would be
invoked only on instance
creation, but sometimes it was invoked for "non-fresh" instance on borrowing.

I also attach small reproduction code below.
Can anyone tell it is because some lack of configurations, or, actual
pool's bug?

Thanks in advance.
----
Noriyuki Torii

----
import java.io.*;
import java.util.*;

import org.apache.commons.pool2.*;
import org.apache.commons.pool2.impl.*;

public class reproduction
{
    private static class MyPooledObj
    {
        volatile int i = 0;
        final String uuid = UUID.randomUUID().toString();
    }

    private static class MyFactory extends BasePooledObjectFactory<MyPooledObj>
    {
        @Override
        public MyPooledObj create() {
            return new MyPooledObj();
        }

        @Override
        public PooledObject<MyPooledObj> wrap(MyPooledObj o) {
            return new DefaultPooledObject<MyPooledObj>(o);
        }

        @Override
        public boolean validateObject(PooledObject<MyPooledObj> o) {
            MyPooledObj myobj = o.getObject();
            synchronized (myobj) {
                myobj.i++;
            }
            System.out.println("Validated.");
            return true;
        }
    }

    public static void main(String[] args)
        throws Exception
    {
        GenericObjectPoolConfig poolCfg = new GenericObjectPoolConfig() ;
        poolCfg.setMaxTotal(1);
        poolCfg.setMaxIdle(1);
        poolCfg.setBlockWhenExhausted(true);
        poolCfg.setMaxWaitMillis(10000);

        poolCfg.setTestOnCreate(true); // should be validated only on creation
        poolCfg.setTestOnBorrow(false);
        poolCfg.setTestOnReturn(false);
        poolCfg.setTestWhileIdle(false);

        final GenericObjectPool<MyPooledObj> pool =
            new GenericObjectPool<MyPooledObj>(new MyFactory(), poolCfg);

        final MyPooledObj o = pool.borrowObject();
        System.out.printf("%d: %s\n", o.i, o.uuid);

        Timer t = new Timer();
        t.schedule
            (new TimerTask() {
                    public void run() {
                        pool.returnObject(o);
                    }
                }, 3000);

        // validation will occur again for non-fresh instance,
        // confirmed on commons-pool2-2.2 with jdk1.7.0_55
        MyPooledObj o2 = pool.borrowObject();
        System.out.printf("%d: %s\n", o2.i, o2.uuid);
        pool.returnObject(o2);
        pool.close();

        t.cancel();
    }
}

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