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From "Philippe Mouawad (JIRA)" <>
Subject [jira] Commented: (DBCP-294) Memory leak in XA Implementation
Date Fri, 12 Jun 2009 15:14:07 GMT


Philippe Mouawad commented on DBCP-294:

My patch proposition would be:
    public synchronized void registerConnection(Connection connection, XAResource xaResource)
        if (connection == null) throw new NullPointerException("connection is null");
        if (xaResource == null) throw new NullPointerException("xaResource is null");
        xaResources.put(connection, new WeakReference(xaResource));

When a Transaction completes:
1) XA Manager will remove strong reference on xaResource.
2) WeakReference can then be garbage collected
3) Finally key will be removed

Philippe Mouawad

> Memory leak in XA Implementation
> --------------------------------
>                 Key: DBCP-294
>                 URL:
>             Project: Commons Dbcp
>          Issue Type: Bug
>    Affects Versions: 1.3, 1.4, 2.0
>         Environment: JDK5, Oracle 10G
>            Reporter: Philippe Mouawad
>            Priority: Critical
> Hello,
> We are been using Ofbiz with DBCP based implementation.
> Ofbiz uses a Head revision of DBCP (package org.apache.commons.dbcp.managed is the same
as current TRUNK) and geronimo-transaction-1.0.
> We are having recurrent OutOfMemory which occur on a 2 days basis.
> I analyzed the Heap Dump and I think have found the source of the problem:
> The Heap Dump shows a Retained Heap of 400Mo by org.apache.commons.dbcp.managed.TransactionRegistry#xaResources
> After analyzing more deeply, the leak seems to come from what is stored in xaResources
> xaResources.put(connection, xaResource);
> Values inside weak Hash map  will never be removed since XAResource holds a STRONG reference
on key (connection) through:
> org.apache.commons.dbcp.managed.LocalXAConnectionFactory$LocalXAResource through:
> public LocalXAResource(Connection localTransaction) {
>             this.connection = localTransaction;
>         }
> Found in WeakHashMap javadoc:
> Implementation note: The value objects in a WeakHashMap are held by ordinary strong references.
>>>>>>>>>>>>>Thus care should be taken to ensure that
value objects do not strongly refer to their own keys <<<<<<<<, either
directly or indirectly, since that will prevent the keys from being discarded. Note that a
value object may refer indirectly to its key via the WeakHashMap itself; that is, a value
object may strongly refer to some other key object whose associated value object, in turn,
strongly refers to the key of the first value object. One way to deal with this is to wrap
values themselves within WeakReferences before inserting, as in: m.put(key, new WeakReference(value)),
and then unwrapping upon each get. 
> Philippe Mouawad

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