Chris Darroch commented on ZOOKEEPER-318:

Cool, thanks.  Much appreciated.

> remove locking in zk_hashtable.c or add locking in collect_keys()
> -----------------------------------------------------------------
>                 Key: ZOOKEEPER-318
>                 URL: https://issues.apache.org/jira/browse/ZOOKEEPER-318
>             Project: Zookeeper
>          Issue Type: Bug
>          Components: c client
>    Affects Versions: 3.0.0, 3.0.1, 3.1.0
>            Reporter: Chris Darroch
>            Assignee: Chris Darroch
>             Fix For: 3.2.0
>         Attachments: ZOOKEEPER-318.patch
> From a review of zk_hashtable.c it appears to me that all functions which 
> manipulate the hashtables are called from the IO thread, and therefore any 
> need for locking is obviated.
> If I'm wrong about that, then I think at a minimum collect_keys() should 
> acquire a lock in the same manner as collect_session_watchers().  Both 
> iterate over hashtable contents (in the latter case using copy_table()).
> However, from what I can see, the only function (besides the init/destroy 
> functions used when creating a zhandle_t) called from the completion thread 
> is deliverWatchers(), which simply iterates over a "delivery" list created 
> from the hashtables by collectWatchers().  The activateWatcher() function 
> contains comments which describe it being called by the completion thread, 
> but in fact it is called by the IO thread in zookeeper_process().
> I believe all calls to collectWatchers(), activateWatcher(), and 
> collect_keys() are made by the IO thread in zookeeper_interest(), 
> zookeeper_process(), check_events(), send_set_watches(), and handle_error().  
> Note that queue_session_event() is aliased as PROCESS_SESSION_EVENT, but 
> appears only in handle_error() and check_events().
> Also note that handle_error() is called only in zookeeper_process() and 
> handle_socket_error_msg(), which is used only by the IO thread, so far as I 
> can see.

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