[PD] variable receive objects?

Miller Puckette msp at ucsd.edu
Wed Jun 20 19:53:14 CEST 2012

Hi Ico and list -
On Tue, Jun 19, 2012 at 10:20:07PM -0400, Ivica Ico Bukvic wrote:
> > -----Original Message-----
> > From: Miller Puckette [mailto:msp at ucsd.edu]
> > Sent: Tuesday, June 19, 2012 5:11 PM
> > To: Ivica Ico Bukvic
> > Cc: 'Claude Heiland-Allen'; Hans-Christoph Steiner; pd-list at iem.at
> > Subject: Re: [PD] variable receive objects?
> > 
> > I don't think your patch works in every case (I think you simply have to
> check
> > every e->e_who inside functions like bindlist_bang() before dereferencing
> > them since someone could clear one of them while inside a previous one).
> Thanks for the update, Miller. Is there a way you could give me an example
> patch that would fail this way? I ask this simply because I am unable to
> imagine one you describe here. Namely, even if a parent's send has been
> changed by the child-of-a-child object this way, this change would only make
> specific instance point to null object but its pointer would be still valid
> until its entire sub-tree has been navigated, and only after its entire
> sub-tree has been navigated would it be actually dereferencing stuff and
> fixing the pointers accordingly before the next incoming wave of calls.
I don't have an example handy but here's a stack pseudo-trace:

pd_bang(first item in bindlist)
toggle_receive()  <--- zeros out second item in bindlist

then when pd_bang returns, bindlist_bang proceeds to dereference second
item in bindlist and... not bang but more like 'boom'.

> > 
> > Also, there are declarations after functional lines, e.g.,
> > 
> > +	change_bindlist_via_graph = 1;
> >      t_bindelem *e;
> > 
> > which is not standard C - something I frequently have to clean up in
> people's
> > patches :)
> You mean declaration of a global variable needs to be placed at the top of
> the source file? Sure, that is an easy fix. It's been placed here in
> proximity to make the patch more legible.
It's an automatic variable whose declaration should be at the beginning of a
block.  Otherwise Visual C++ seems to get offended (and I don't find out
until I crank up my stupid windows machine :)

> > 
> > I think something like what you proposed could work; there would still be
> a
> > performance hit which I'd probably want to measure before committing to
> > doing this... since after all we're just talking about a wierd and
> obnoxious
> > 'feature'
> > in IEMGUIs that I would simply take out if I could :)
> I am not so sure there is a performance hit since in both cases
> dereferencing happens in exactly the same way, except in this one the
> referencing is delayed and in the interim structs destined to be
> dereferenced are made to point to null and then skipped if a subsequent call
> trips over a null-pointing struct before it has been dereferenced. As such
> its performance impact should be minimal.
Main performance hit would be that every time anyone traverses a bindlist
(many send/receive messages, perhaps most) there's all that extra code in
bindlist_bang(), etc. needed to make the extra tests (possible zero receiver
and possible cleanup needed afterward).


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