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https://issues.apache.org/jira/browse/ZOOKEEPER-900?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16623686#comment-16623686
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Yun Qin commented on ZOOKEEPER-900:
-----------------------------------
I believe we have met an issue very similar to what's described in section b)
of the original bug description. In our case, sid 1/2 weren't able to rejoin a
quorum consisting of sid 3/4/5. The root cause was that
QuorumCnxManager$Listener wasn't able to accept connection from sid 1/2 on sid
3/5. Restarting ZooKeeper on sid 3/5 solved the issue.
I would really appreciate it if we can proceed with the fix, now that we have a
preliminary patch and people willing to take over. Thanks.
> FLE implementation should be improved to use non-blocking sockets
> -----------------------------------------------------------------
>
> Key: ZOOKEEPER-900
> URL: https://issues.apache.org/jira/browse/ZOOKEEPER-900
> Project: ZooKeeper
> Issue Type: Bug
> Reporter: Vishal Kher
> Assignee: Martin Kuchta
> Priority: Critical
> Fix For: 3.6.0, 3.5.5
>
> Attachments: ZOOKEEPER-900-part2.patch, ZOOKEEPER-900.patch,
> ZOOKEEPER-900.patch1, ZOOKEEPER-900.patch2
>
>
> From earlier email exchanges:
> 1. Blocking connects and accepts:
> a) The first problem is in manager.toSend(). This invokes connectOne(), which
> does a blocking connect. While testing, I changed the code so that
> connectOne() starts a new thread called AsyncConnct(). AsyncConnect.run()
> does a socketChannel.connect(). After starting AsyncConnect, connectOne
> starts a timer. connectOne continues with normal operations if the connection
> is established before the timer expires, otherwise, when the timer expires it
> interrupts AsyncConnect() thread and returns. In this way, I can have an
> upper bound on the amount of time we need to wait for connect to succeed. Of
> course, this was a quick fix for my testing. Ideally, we should use Selector
> to do non-blocking connects/accepts. I am planning to do that later once we
> at least have a quick fix for the problem and consensus from others for the
> real fix (this problem is big blocker for us). Note that it is OK to do
> blocking IO in SenderWorker and RecvWorker threads since they block IO to the
> respective peer.
> b) The blocking IO problem is not just restricted to connectOne(), but also
> in receiveConnection(). The Listener thread calls receiveConnection() for
> each incoming connection request. receiveConnection does blocking IO to get
> peer's info (s.read(msgBuffer)). Worse, it invokes connectOne() back to the
> peer that had sent the connection request. All of this is happening from the
> Listener. In short, if a peer fails after initiating a connection, the
> Listener thread won't be able to accept connections from other peers, because
> it would be stuck in read() or connetOne(). Also the code has an inherent
> cycle. initiateConnection() and receiveConnection() will have to be very
> carefully synchronized otherwise, we could run into deadlocks. This code is
> going to be difficult to maintain/modify.
> Also see: https://issues.apache.org/jira/browse/ZOOKEEPER-822
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