[asdf-devel] Ordering of system :depends-on elements

[Faré]

On Wed, Jul 17, 2013 at 11:56 AM, Attila Lendvai
<attila.lendvai at gmail.com> wrote:
>> ASDF's process for constructing a build plan from partial-order
>> dependencies is (unless Faré changed something when I wasn't
>> looking) non-deterministic.
>
> does it mean that it's actively randomized?
>
No, there was never active randomization, but the infamous
union-of-dependencies function used in practice to reverse the order
in which depends-on is consulted as compared to the order in which it
is specified.

> i remember in our busier days (well before ASDF3) we used to have
> load order anomalies that seemed like they depended on filesystem
> order or something external to lisp.
>
There used to be many anomalies related to timestamps. ASDF3 should
have that fixed, at least.

> the symptom was that on my dev machine stuff compiled/loaded fine
> reproducibly, then when the recorded changes got pulled to the live
> server it suddenly failed to compile/load due to a dependency that was
> not explicitly added to the .asd file.
>
> i don't really remember if it was just partial reloading, or clean
> recompile/reload, but i think it was the former, because it was rather
> baffling and the former wouldn't be too baffling.
>
This description is not enough for me to identify what bug (or
"feature") you may have been hitting. Inter-system dependencies used
to just not be done correctly; also, timestamps could be "interesting"
when compiling in one image and loading in another. Finally, time skew
between filesystem server and local kernel could be very
"interesting". All things that should now be fixed with ASDF3.

> if the ordering is actually not deterministic (as opposed to merely
> unspecified), then maybe it's a good idea to actively randomize
> lists before dependency constraints are applied?
>
It is merely unspecified, and happened to be reversed in ASDF1 and
after it ASDF2, as compared to user order (however, components would
still be traversed in user order).

(In ASDF2, I incrementally refactored the traversal algorithm until I
understood it, and some bugs were fixed in corner cases, but the
algorithm mainly stayed the same. In ASDF3, to fix a "last" couple of
bugs, I had to completely rewrite the algorithm, twice, and all the
traversal bugs and quirks should be gone now. See my ASDF3 talk at ELS
2013.)

—♯ƒ • François-René ÐVB Rideau •Reflection&Cybernethics• http://fare.tunes.org
An apple every eight hours will keep three doctors away.