[jira] [Commented] (ZOOKEEPER-900) FLE implementation should be improved to use non-blocking sockets

["Reed Wanderman-Milne (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/ZOOKEEPER-900?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14130830#comment-14130830 ] 

Reed Wanderman-Milne commented on ZOOKEEPER-900:
------------------------------------------------

Hi,

I'm wondering if there's any progress on this JIRA. I'm running into an issue similar to that of ZOOKEEPER-1678, which can be solved by fixing this. If no one is working on it, I'd be happy to take a stab at it.

[~vishalmlst]'s patch added a timeout for connections to other peers, but it still seems appears that only one connection can be processed at a time. Additionally, in connectOne(long), a lock on the QuorumPeer is held, preventing other threads from accessing it. Both this issues seem to contribute to ZOOKEEPER-1678. [~vishalmlst] suggested in an earlier comment to move the socket operations to SenderWorker and RecvWorker, which would prevent socket operations from blocking other connections.

Let me know what your thoughts are. 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: Vishal Kher
>            Priority: Critical
>             Fix For: 3.5.1
>
>         Attachments: 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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