[jira] [Created] (POOL-413) [GOP] Race condition while returning objects. maxIdle is ignored

["Adrien Bernard (Jira)" <ji...@apache.org>]

Adrien Bernard created POOL-413:
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             Summary: [GOP] Race condition while returning objects. maxIdle is ignored
                 Key: POOL-413
                 URL: https://issues.apache.org/jira/browse/POOL-413
             Project: Commons Pool
          Issue Type: Bug
            Reporter: Adrien Bernard
         Attachments: 0001-Add-test-to-reproduce-concurrency-issue-when-returni.patch

In a GenericObjectPool it is possible to configure a maximum number of idle objects to be kept by the pool while they are not in use.

In unfortunate circumstances, if several threads return an object to the pool at the same time, the check on the maximum number of idle objects may be dismissed. This results in pool keeping more idle objects than configured.

I have build a unit test to reproduce the issue. I attach it as a patch made on top of release 2.12.0. On my machine it randomly fails with a 10% rate.

Looking into the source code of the returnObject method of the GOP, it seems that there is no synchronisation between the moment the check is made for the maxIdle configuration and the moment the object is destroyed :
{code:java}
final int maxIdleSave = getMaxIdle();
if (isClosed() || maxIdleSave > -1 && maxIdleSave <= idleObjects.size()) {
    try {
        destroy(p, DestroyMode.NORMAL);
    } catch (final Exception e) {
        swallowException(e);
    }
    try {
        ensureIdle(1, false);
    } catch (final Exception e) {
        swallowException(e);
    }
} {code}
Have you thoughts on this ?



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