Re: [Swarm-Support] How to prevent sending a message to a dropped object?

[Paul Johnson]

I think I'd redesign it so that dead mothers were never sent messages. 
That is, remove the dead ones from the lists being processed.

But I think you can brute force fix this like so. Instead of having this 
message put "haveChild" with target "mother__" on schedule, have it aime 
the message at something you are sure exists, say model swarm.

[lifeMutationSchedulw at: (time + (int) (0.25* DPY*MPD)) createActionTo: 
self message: M(considerChildbirth):mother];


Then in that method

(void)considerChildbirth: mother
{
   if (mother) [mother haveChild];
   else fprintf(stderr,"you just tried to give birth from the dead, 
silly!");
}

If "mother" is a pointer to nil, then this will prevent the seg fault.

Won't it?

pj

martijn cox wrote:
> Hi,
>
> Im new here so if I break any form of etiquette, please forgive me :)
>
> I've been working on a (very simple) swarm-based simulation of evolution,
> and have come accross the following problem. Female animals can have babies,
> after impregnation by a male. This impregnation is a combining of the neural
> networks of the parents, and this new neural network is stored in the
> female. during here. During her pregnancy, the female can die, and carry her
> unborn child with her (*sob*).
>
> The problem is, that I'd like to have the pregnancy scheduled by the model
> by the following ActionCreateTo:
> --------------------------------------------
> -scheduleBirthFromMother: (id) mother__
> {
> *snip*
> [lifeMutationSchedule at: (time + (int) ( 0.25 * DAYSPERYEAR *
> MINUTESPERDAY ))
>    createActionTo: mother__
>    message: M(haveChild)];
> *snip*
> }
> --------------------------------------------
> and if the female dies somewhere between impregnation and giving birth, this
> message is send to a voided reference (because the female has long and gone
> been dispatched of by a reaperQueue).
> The final result is that every call subsequent call to create sends my
> program crashing to its segmentation faulty damnedness, I presume because a
> method has been called on with self = nil and as a consequence, the stack
> has become corrupt.
>
> A short term solution I've been using so far, is to not wipe the
> reaperqueue, but keep all agents in cryostatis for the length of the
> simulation (so the speak). Another solution would be to undo the
> ActionCreateTo, but I see no way in all documentation I've searched through
> how this can be done.
>
> If no one can help me, I will probably resort to waiting untill after the
> message has been sent to the dead agent before I wipe it from memory, but I
> don't think that would be a very clean solution.
>
> Kind regards,
>
> Martijn Cox
>
> ps: my gratitude for supplying the incredibly usefull environment to anyone
> who has ever contributed to swarm! :)
> _______________________________________________
> Support mailing list
> address@hidden
> http://www.swarm.org/mailman/listinfo/support


--
Paul E. Johnson                       email: address@hidden
Dept. of Political Science            http://lark.cc.ku.edu/~pauljohn
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