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Posted to dev@qpid.apache.org by "Robbie Gemmell (JIRA)" <qp...@incubator.apache.org> on 2010/06/09 16:58:13 UTC
[jira] Commented: (QPID-2653) Double checked locking in
org.apache.qpid.server.transport.ThreadPoolFilter
[ https://issues.apache.org/jira/browse/QPID-2653?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12877095#action_12877095 ]
Robbie Gemmell commented on QPID-2653:
--------------------------------------
The original code, whilst a bit odd looking, does ensure that only 1 new buffer is added to the map. The patch does not, as it synchronizes after checking whether tehre was anything in the map and so multiple threads waiting on the lock could then add to the map. I would look at synchronizing/locking around the get and put.
> Double checked locking in org.apache.qpid.server.transport.ThreadPoolFilter
> ---------------------------------------------------------------------------
>
> Key: QPID-2653
> URL: https://issues.apache.org/jira/browse/QPID-2653
> Project: Qpid
> Issue Type: Bug
> Components: Java Broker
> Affects Versions: 0.7
> Reporter: Sorin Suciu
> Priority: Minor
> Fix For: 0.7
>
> Attachments: 0001-Double-checked-locking-in-org.apache.qpid.server.tra.patch
>
>
> org.apache.qpid.server.transport.ThreadPoolFilter has a double check locking in this method:
> private SessionBuffer getSessionBuffer(IoSession session)
> {
> final Map buffers = this.buffers;
> SessionBuffer buf = (SessionBuffer) buffers.get(session);
> if (buf == null)
> {
> synchronized (buffers)
> {
> buf = (SessionBuffer) buffers.get(session);
> if (buf == null)
> {
> buf = new SessionBuffer(session);
> buffers.put(session, buf);
> }
> }
> }
> return buf;
> }
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