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Posted to dev@qpid.apache.org by "ASF subversion and git services (JIRA)" <ji...@apache.org> on 2013/10/29 16:24:31 UTC
[jira] [Commented] (QPID-5139) HA transactions block a thread, can
deadlock the broker.
[ https://issues.apache.org/jira/browse/QPID-5139?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13808078#comment-13808078 ]
ASF subversion and git services commented on QPID-5139:
-------------------------------------------------------
Commit 1536751 from [~aconway] in branch 'qpid/trunk'
[ https://svn.apache.org/r1536751 ]
QPID-5139: Add unit test for deadlock caused by blocking HA commit.
> HA transactions block a thread, can deadlock the broker.
> --------------------------------------------------------
>
> Key: QPID-5139
> URL: https://issues.apache.org/jira/browse/QPID-5139
> Project: Qpid
> Issue Type: Bug
> Components: C++ Clustering
> Affects Versions: 0.24
> Reporter: Alan Conway
> Assignee: Alan Conway
> Priority: Critical
> Fix For: 0.25
>
>
> When the client sends a "prepare" command for a transaction, the thread handling that command is blocked until all backups have responded with their prepare status. This can easily deadlock the broker if there are more concurrent transactions than worker threads.
> To reproduce you need a way to delay completion of a transaction. The following regression test illustrates, it will be added to TransactionTests in ha_tests.py as part of the fix:
> {noformat}
> def test_tx_block_threads(self):
> """Verify that TXs blocked in commit don't block broker threads."""
> cluster = HaCluster(self, 2, args=["--worker-threads=2"])
> sessions = [cluster[0].connect().session(transactional=True) for i in xrange(2)]
> for s in sessions: s.sender("foo;{create:always}").send("foo")
> self.assertEqual(2, len(cluster[1].agent().tx_queues()))
> os.kill(cluster[1].pid, signal.SIGSTOP) # Freeze backup so tx can't complete.
> threads = [ Thread(target=s.commit) for s in sessions]
> for t in threads: t.start()
> cluster[0].ready(timeout=1) # Should not block
> os.kill(cluster[1].pid, signal.SIGCONT) # Allow tx to complete.
> for t in threads: t.join()
> c.close()
> {noformat}
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