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From "Henry Robinson (JIRA)" <j...@apache.org>
Subject [jira] Commented: (ZOOKEEPER-763) Deadlock on close w/ zkpython / c client
Date Wed, 05 May 2010 18:08:04 GMT

    [ https://issues.apache.org/jira/browse/ZOOKEEPER-763?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12864429#action_12864429
] 

Henry Robinson commented on ZOOKEEPER-763:
------------------------------------------

Hi Kapil - 

As seems to be the norm for me this week, I'm struggling to reproduce :) It does seem like
your python script explicitly waits for a completion to be called before closing a handle.
Is this enough to leave an outstanding completion on the queue?

Can you capture the stacktrace for the completion thread? I think it must be getting stuck
in process_completions but it would be very valuable to know where - if it's stuck on the
callback into zkpython then that means the deadlock is in the python bindings and not solely
in C-land.

cheers,
Henry

> Deadlock on close w/ zkpython / c client
> ----------------------------------------
>
>                 Key: ZOOKEEPER-763
>                 URL: https://issues.apache.org/jira/browse/ZOOKEEPER-763
>             Project: Zookeeper
>          Issue Type: Bug
>          Components: c client, contrib-bindings
>    Affects Versions: 3.3.0
>         Environment: ubuntu 10.04, zookeeper 3.3.0 and trunk
>            Reporter: Kapil Thangavelu
>            Assignee: Mahadev konar
>             Fix For: 3.4.0
>
>         Attachments: deadlock.py, stack-trace-deadlock.txt
>
>
> deadlocks occur if we attempt to close a handle while there are any outstanding async
requests (aget, acreate, etc). Normally on close both the io thread terminates and the completion
thread are terminated and joined, however w\ith outstanding async requests, the completion
thread won't be in a joinable state, and we effectively hang when the main thread does the
join.
> afaics ideal behavior would be on close of a handle, to effectively clear out any remaining
callbacks and let the completion thread terminate.
> i've tried adding some bookkeeping to within a python client to guard against closing
while there is an outstanding async completion request, but its an imperfect solution since
even after the python callback is executed there is still a window for deadlock before the
completion thread finishes the callback.
> a simple example to reproduce the deadlock is attached.

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