Re: Thank you for trying out SWISH - here are the bugs

Hi Torbjörn,

Good to see it attracts attention!

Destroying message queues is supposed to be safe at all times.  This
is a bug.  Only, I need something to reproduce it, or at least a core
dump in which I can poke around to examine the state of the system.

(to do that, compile for debugging as indicated in build, enable core
dumps using "ulimit -c unlimited" and provide me with a login).

	--- Jan

On 07/20/2013 09:36 AM, Torbjörn Lager wrote:
> Hi All,
> 
> Thanks to all of you who played with SWISH. The test release went well
> I think, since only two bugs unknown to me has surfaced so far.
> Norbert Fuchs found that when saving a program containing "\+" the
> +-sign disappeared. Likely an encoding issue. Will fix it tomorrow or
> on Monday.
> 
> A more serios bug is related to the ending of sessions. Three times
> last night the server crashed with the following message:
> 
> [Thread 19] pl-thread.c:2899: destroy_message_queue: Assertion failed:
> !queue->waiting && !queue->wait_for_drain
> Stack trace labeled "crash":
>   [0] swipl() [0x80eea93]
>   [1] swipl() [0x80bcf0a]
>   [2] swipl() [0x80bf0df]
>   [3] swipl() [0x80c0b57]
>   [4] swipl() [0x80c1d4b]
>   [5] /lib/i686/cmov/libpthread.so.0(+0x5955) [0xb763b955]
>   [6] /lib/i686/cmov/libc.so.6(clone+0x5e) [0xb75bbe7e]
> Aborted
> 
> I *think* that this occured when a session timed out (after ten
> minutes of inactivity) and was supposed to clean up a few resources.
> The relevant code is here:
> 
> %   When a client session ends, the currently running goal (if any)
> %   is aborted, the output queue is destroyed, and the client module
> %   is emptied.
> 
> :- listen(http_session(end(SessionId, _Peer)), end_session(SessionId)).
> 
> end_session(SessionId) :-
>     catch(thread_signal(SessionId, abort), _, true),
>     atom_concat(SessionId, '.out', Output),
>     message_queue_destroy(Output),
>     forall(current_predicate(SessionId:PI),
>         (   memberchk(PI, [read/1, write/1, writeln/1, nl/0])
>         ->  true
>         ;   abolish(SessionId:PI)
>         )
>     ).
> 
> The message queue is created when the session begins and as far as I
> can see it should be possible to destroy it in this way. Maybe you can
> spot the problem?
> 
> I will have to return to this on Monday. I will leave the server
> running, but I guess it is likely to crash again and then I won't be
> here to restart it.
> 
> Best,
> Torbjörn
> 
> --
> Torbjörn Lager
> Professor of General and Computational Linguistics
> Department of Philosophy, Linguistics and Theory of Science
> University of Gothenburg
> Box 200, SE-405 30 Gothenburg, Sweden
> Phone: +46317864962
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