[isabelle-dev] AFP devel broken

Gerwin Klein Gerwin.Klein at nicta.com.au
Sat Dec 8 00:53:10 CET 2012

Excellent! Thanks for tracking this down, that was way more involved than I had anticipated. I'll do some more explicit testing of the AFP over the weekend to confirm.


On 08/12/2012, at 9:50 AM, Makarius <makarius at sketis.net> wrote:

> On Thu, 6 Dec 2012, Tobias Nipkow wrote:
>> Am 06/12/2012 12:57, schrieb Makarius:
>>> This does not say anything yet.  We need to collect further details and
>>> hypotheses and test them.  I will also try again to reproduce it myself.
>> One point may (or may not) have got lost. The problem seems to be independent
>> from the AFP. Remember that I had the situation where even HOLCF hung. It turned
>> out that trying to load any theory based on HOL hung. I eventually forced HOL to
>> be recompiled and then things were more normal again. Yes, it sounds strange.
> The situation should be under control again.
> I've introduced this problem myself in a recent cleanup of the future task scheduler, probably around 262c36fd5f26 from 18-Oct-2012.  Since we are lagging behind with the testing infrastructure itself, we often get delays in exposing issues of the systems being tested.
> So this is the explanation for the empirical observations on this thread:
>  * AFP uses document_variants=document:outline=/proof,/ML which means > 1
>    document preparation jobs in the end; thus it had the future task
>    scheduler and potentially some worker threads still running when the
>    image was saved.
>  * After reloading the image to build another session on top, the old
>    tasks were revived by the Poly/ML runtime system, but a fresh instance
>    of the scheduler + workers forked by Isabelle/ML as usual.  The old
>    threads could still hold locks or access critical variables in a way
>    that interferes with the fresh crew.
> What is also funny in the persistent thread model is that the thread equality changes but physically the threads operate on the same data space as before the dump.  This makes it hard to check explicitly against such mistakes inside ML.
> Anyway, in such a situations of Isabelle/ML threading problems (not Poly/ML threading problems nor Scala/JVM threading problems) setting Multithreading.trace := 5 gives an idea what is wrong. Since it was all in my own machine room it was easy to isolate and address -- problems by Oracle or EPFL take much longer.
> So here is my changeset to conclude this mail thread (hopefully):
> # HG changeset patch
> # User wenzelm
> # Date 1354918479 -3600
> # Node ID 702278df3b57aff4c55fec3bffb0206ace927432
> # Parent  f8cd5e53653b98df3433356a94bbb3810042c626
> make double-sure that the future scheduler is properly shutdown, otherwise its threads are made persistent and will deadlock with the fresh instance after reloading the image (NB: Present.finish involves another Par_List.map over document_variants and thus might fork again);
> diff -r f8cd5e53653b -r 702278df3b57 src/Pure/System/session.ML
> --- a/src/Pure/System/session.ML      Fri Dec 07 23:11:01 2012 +0100
> +++ b/src/Pure/System/session.ML      Fri Dec 07 23:14:39 2012 +0100
> @@ -79,6 +79,7 @@
>   Keyword.status ();
>   Outer_Syntax.check_syntax ();
>   Options.reset_default ();
> +  Future.shutdown ();
>   session_finished := true);
>       Makarius
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