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From "Eli Reisman (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (GIRAPH-213) NettyClient.stop() could deadlock according to netty.io docs
Date Thu, 28 Jun 2012 00:52:44 GMT

    [ https://issues.apache.org/jira/browse/GIRAPH-213?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13402729#comment-13402729
] 

Eli Reisman commented on GIRAPH-213:
------------------------------------

No, according to netty.io the method used in the NettyClient.stop() is not safe and can deadlock.
They recommend never using it. Even though the future method looks funky, a read of the docs
indicates the futures get their event calls either way also. So as long as we use the Atomic
counter to make sure we don't release resources before every Future gets its event call, we
are safe. I ran this patch with jobs and also with full 'mvn verify' tests and it seems to
work fine, no problems. Again, its not about the open/closed status of the connections, its
just about when to release the resources, so instant return from the call doesn't hurt us.
Apparently the existing call looks reasonable (barrier until resources can be released) it
is deprecated.

The NettyServer does it too, but at least it sets a timeout per-call. Problem is, this holds
up the return of the call while NOT guaranteeing the connections are actually closed in time
for the resource release, which is bad. There is a separate ChannelGroupFuture I could use
to fix that one too, but I thought I would start with this one as it had no timeout and deadlock
is a bigger risk (I assume?) than releasing resources before the Channels are guaranteed to
be closed, though neither is good.

Let me know what you decide.

                
> NettyClient.stop() could deadlock according to netty.io docs
> ------------------------------------------------------------
>
>                 Key: GIRAPH-213
>                 URL: https://issues.apache.org/jira/browse/GIRAPH-213
>             Project: Giraph
>          Issue Type: Improvement
>    Affects Versions: 0.2.0
>            Reporter: Eli Reisman
>            Assignee: Eli Reisman
>            Priority: Trivial
>             Fix For: 0.2.0
>
>         Attachments: GIRAPH-213-1.patch
>
>
> NettyClient.stop() does not follow netty.io best practices and could potentially deadlock?

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