[PD] variable outlets in dsp object

David Medine dmedine at ucsd.edu
Thu Jun 8 11:19:17 CEST 2017


Now I realize that everything I posted in the last post makes absolutely 
no sense at all. Something else is causing the crashes. Damn!


On 6/8/17 10:51 AM, David Medine wrote:
>
> I am writing a DSP extern that can have a any number of outlets 
> depending on the creation arguments (like [fexpr~], e.g.). In order to 
> interact with the outlets in the XXX_tilde_perform loop, I made a 
> member of my t_XXX_tilde data structure thus:
>
> t_sample **lcl_outs;
>
> Then, when I know how many outlets I need, I allocate the appropriate 
> amount of memory. In theXXX_tilde_perform loop, I set the pointers to 
> those handed by Pd's scheduling engine in the standard way:
>
> for(int i=0;i<x->nouts;i++)
>
>     x->lcl_outs[i] = w[2+i];
>
> I found that this would sporadically crash Pd when turning the DSP 
> engine on and off and (sometimes) when connecting/disconnecting to one 
> of the outlets. I think that I have solved this problem by copying my 
> pointers at the head of the XXX_tilde_perform method to a local variable:
>
> t_sample **lcl_outs = x->lcl_outs;
>
> for(int i=0;i<x->nouts;i++)
>
>     lcl_outs[i] = w[2+i];
>
> Everything /appears/ to work now. I assume that somehow Pd's engine is 
> rubbing my x->lcl_outs ptr off of the stack. Thus, by copying it to 
> another ptr I avoid this problem because my OS still knows where the 
> allocated memory is. That is to say, when Pd gets rid of whateverw[2] 
> is, it then removes the ptr lcl_outs, not x->lcl_outs, which still has 
> memory behind it.
>
> Am I reading this right? I am not at all confident that I have truly 
> solved this problem. If anyone has any insight, I'd like to know too.
>
> Thanks!
>
> David
>
>
>
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