widelands-dev team mailing list archive

[Tibor Bamhor <tiborb95@xxxxxxxxx>]

Well, AI never ever before checked if a bulding listed in productionsites
really exists. There is another part of code (functions lose_building and
gain_buildings) that are called by core and are updating productionsites
list. Widelands has been working this way for years and nobody ever felt a
need to change that (or I as a newcomer do not know about this).


We are talking abut something else, see this line:


ProductionSiteObserver& site = productionsites.front();


Our question is "Is iterator 'site' valid all the time
check_productionsites() function is being executed?


I googled quite a lot and it seems there is not a good way to verify
validity of such iterator, only programmer has to be carefull with
manipulating std::list. Manipulation (push_back, pop_back) can make such
iterator invalid.


Also note that during running AI (DefaultAI::think() and all called
functions) no building is finished or destroyed. AI calls
"send_player_dismantle(*site.site)" and building is dismantled (in fact in
two stages) later, and IA is notified about change via lose_building() and
productionsites list is updated (this is done out of DefaultAI::think()
function). At the end the game is single-threaded, is not it?


Also note that there is update_productionsite_stats() functions that f.e.
queries statistics of buildings in productionsites and if it queried
nonexisting building it would lead to segmentation fault or other problems.


So brief summary at the end :):

we are talking about different issues: I talk about validity of std:list
iterator, you about possibility that productionsites contains nonexistant
building.


Regards


Tibor




2014-06-30 7:11 GMT+02:00 Holger Rapp <SirVer@xxxxxx>:

> (should I send the replay to mailing list?)
>
>
> yes :). Contacting one dev individually is nearly always the wrong
> decision.
>
> Also, you should make a merge request if you want to have your branch
> reviewed. And it should be ready for inclusion into trunk from your point
> of view, otherwise reviewing is a waste of time.
>
> But the summary of situation is here:
>
> My tiborb-ai branch (merged to trunk in revision 6978) contained a bug
> that did not show on linux only on other platforms.
>
> You tried to fix it in revison 6989, but the fix is wrong, valgrind
> reports memory issues and the std::list productionsites is treated
> incorrectly, every time a building is to be checked (all production
> buildings are checked periodically), the buiding is deleted from list and
> this leads to absurd behaviour. AI just doesnt know about own buildings.
> Visible effect is that no mines are built because mines are built only if
> there are 8 production buildings. And AI just believes actual number of
> buildings is too low (decreasing by one by every regular productionsites
> check - done every +- 20 seconds).
>
>
> Most buildings should be repushed at the end of the list before returning
> the function. But my changes might easily contain errors of course - I find
> the AI code hard to understand and there are no tests, so refactorings
> break things. Note that no dev has the right to complain about his/her code
> to be broken by others if there are no tests :).
>
> In tibor-ai2 I added further changes to the AI logic and hopefully fixed
> the crashing. Tested under valgrind, gdb - tenths of hours of gameplay and
> other hundereds without debug tool. But I cannot test it under other
> platforms.
>
>
> While that sounds like a lot of testing, reality shows that just letting
> the game run is usually poor testing - it will not test corner cases often
> enough. And hundreds of hours is is just 1 hour for a hundred people - i.e.
> they will hit corner cases much quicker. Adding tests for your new features
> (AND doing the run the game for a while tests) is usually much better.
>
> So options are:
> a) we go object pointers way (your design) but somebody (you?) should fix
> it in trunk first, I am not able to
> b) we omit object pointers and stay with old design - this is what is done
> in my branch.
>
>
> Why not do both and use object ptrs? They are the correct choice in the
> sense of defense programming. I am fine with your changes as long as they
> do not crash the game. A bad AI is preferable to a crashing one for sure
> though.
>
> What I suggest: somebody should test under windows/mac and find out it it
> still crashes and if not - I will merge trunk into my branch - option b.
>
> And this is also reason why I did not do any merging of trunk to my branch.
>
>
> Personally - I spend some time working on this, I feel it is in reasonable
> state and would like to have it merged finally.
>
>
> Okay, then propose it for reviewing and request windows and mac feedback.
> You will likely not get much until it is merged and hits the nightlies
> though - then is when people are really starting to play with it.
>
>
>
>
> Tibor
>
>
> 2014-06-28 8:12 GMT+02:00 Holger Rapp <SirVer@xxxxxx>:
>
>> Please merge Trunk Now. Make it a habit to keep your branch up to date
>> with trunk by always merging. It will make reviewing easier by making the
>> diff as realistic and small as possible.
>>
>> Also, explaining why trunk ai is broken and how you fixed it will make it
>> easier to comment on this part directly.
>>
>> > Am 27.06.2014 um 23:22 schrieb Tibor Bamhor <tiborb95@xxxxxxxxx>:
>> >
>> > Hi all,
>> >
>> > Please review latest changes I did to AI in branch tibor-ai2
>> >
>> > bzr branch lp:~widelands-dev/widelands/tibor-ai2
>> >
>> > AI in trunk is still badly broken and I think it is time to fix it.
>> >
>> > I am interested especially in stability on Windows and Mac platform, as
>> this was a problem with previous iteration of AI.
>> >
>> > If everything is OK, I will merge trunk there and propose merging into
>> trunk
>> >
>> > Thanks!
>> >
>> > Tibor
>> > _______________________________________________
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>
>
>