Thank you for trying out SWISH - here are the bugs

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