Christian Wiedmann commented on ZOOKEEPER-542:

I don't really know how to do an automated test for this, since the spinning is 
not visible outside of the API.  The manual test I used is to kill -STOP the 
server and then wait until the client tries to reconnect while running strace 
on the I/O thread (I'm using python bindings, btw).  Pre-patch the strace shows 
repeated calls to poll, with POLLOUT set on the server fd.  Post-patch, POLLOUT 
is not set, and there is no spinning.

> c-client can spin when server unresponsive
> ------------------------------------------
>                 Key: ZOOKEEPER-542
>                 URL: https://issues.apache.org/jira/browse/ZOOKEEPER-542
>             Project: Zookeeper
>          Issue Type: Bug
>          Components: c client
>    Affects Versions: 3.2.0, 3.2.1
>            Reporter: Christian Wiedmann
>            Assignee: Christian Wiedmann
>             Fix For: 3.3.0
>         Attachments: ZOOKEEPER-542.patch, ZOOKEEPER-542.patch
> Due to a mismatch between zookeeper_interest() and zookeeper_process(), when 
> the zookeeper server is unresponsive the client can spin when reconnecting to 
> the server.
> In particular, zookeeper_interest() adds ZOOKEEPER_WRITE whenever there is 
> data to be sent, but flush_send_queue() only writes the data if the state is 
> ZOO_CONNECTED_STATE.  When in ZOO_ASSOCIATING_STATE, this results in spinning.
> This probably doesn't affect production, but I had a runaway process in a 
> development deployment that caused performance issues on the node.  This is 
> easy to reproduce in a single node environment by doing a kill -STOP on the 
> server and waiting for the session timeout.
> Patch to be added.

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