[jboss-jira] [JBoss JIRA] (JGRP-1665) UNICAST3 / NAKACK2: problem with flow control and message batching
Bela Ban created JGRP-1665:
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Summary: UNICAST3 / NAKACK2: problem with flow control and message batching
Key: JGRP-1665
URL: https://issues.jboss.org/browse/JGRP-1665
Project: JGroups
Issue Type: Bug
Reporter: Bela Ban
Assignee: Bela Ban
Priority: Critical
Fix For: 3.3.4, 3.4
When a message is received by UNICAST3 or NAKACK2 and passed up to the application, but
the app in turn sends large amounts of data down, then it may block in the flow control
protocol (UFC or MFC).
We did remove ignore_sync_response (in https://issues.jboss.org/browse/JGRP-1655), which
would let sync responses pass through flow control, assuming that credit responses would
be received as OOBs.
However, the issue with credits being received as part of *message batches* is that
they're received as *internal* batches, not *OOB* batches.
This means that they are delivered sequentially (since they're from the same sender)
and are thus not applied until *after* the blocking request returns, which is not the
case: deadlock !
The reason is that credits are marked as INTERNAL (and also OOB), but the code which reads
batches adds all INTERNAL|OOB messages to the internal batch, which is processed by the
internal pool, but since the batch itself is not tagged as OOB, the messages will not get
processed immediately.
SOLUTION: treat INTERNAL the same as OOB, e.g. check for OOB and INTERNAL:
{code}
if(batch.mode() == INTERNAL || batch.mode() == OOB)
{code}
An alternative would be to revisit the idea of the internal thread pool: is it really
needed ? And possibly get rid of it.
Git bisect shows the faulty commit on July 16:
{noformat}
[linux]/home/bela/JGroups$ git bisect good
87cf70d936bb3b15860bf4cd89fe2fff49e85d1e is the first bad commit
commit 87cf70d936bb3b15860bf4cd89fe2fff49e85d1e
Author: Bela Ban <belaban(a)yahoo.com>
Date: Tue Jul 16 14:51:10 2013 +0200
Removed ignore_synchronous_thread and ignore_thread from FlowControl; not needed
anymore as we cannot block anymore on credit responses
(https://issues.jboss.org/browse/JGRP-1655)
:040000 040000 d0e4647ab4b89d320e45a460f0385311e2e4eba0
fefac0eb21ab3609ccf440eec9ec8f659a819f6b M src
{noformat}
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