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.


> 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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