[PD-dev] why must one never send a message from a perform routine ?

[Day Rush]

How well does it work? It looks like the repo is based off of 0.52?
Multithreaded DSP would have been much higher on my list than
multi-channel, so I'm wondering if I could get away with using your tree as
my basis for a while :)

- d

On Tue, 22 Aug 2023 at 01:17, Christof Ressi <info at christofressi.com> wrote:

> To expand on Miller's reply:
>
> Conceptually, messaging and DSP are two separate domains. Sending a
> message from a perform routine violates this separation. Instead you
> should use a clock with delay 0 to defer the message to the begin of the
> next scheduler tick.
>
> Miller already mentioned the greatest danger, but there are other, more
> subtle issues. DSP objects typically operate on the premise that the
> object's state won't change from the outside during the perform routine.
> For example, imagine a delay object with a buffer that can be resized
> with a message; by sending a Pd message from the perform routine, it
> might accidentally feed back into the object and reallocate the buffer
> while still in progress.
>
> Unfortunately, very little of this is documented. Ideally, this should
> be covered in the externals-how-to
> (https://github.com/pure-data/externals-howto); I just added an item on
> my (long) TODO list.
>
> Finally, although Pd is currently single-threaded, this could change in
> the future. FWIW, here is a PoC for multi-threaded DSP:
> https://github.com/spacechild1/pure-data/tree/multi-threading. This is
> only possible because perform routines may only use a restricted set of
> API functions - which, in my fork, are annoted with the (empty)
> THREADSAFE macro (and made thread-safe, if necessary).
>
> Christof
>
> On 21.08.2023 20:55, Joseph Larralde wrote:
> > Hmm, I see ... unfortunately my random bug is totally unrelated to
> > this weakness of my code.
> > Thanks Miller for the explanation and pointers to examples !
> > And thanks Claude for the extra example.
> > I'll check all my objects to see if there are other ones I can
> > consolidate.
> >
> > Cheers !
> >
> > Joseph
> >
> > Le 21/08/2023 à 19:08, Claude Heiland-Allen a écrit :
> >> See bang~ in pure-data/src/d_misc.c for an example that uses a clock
> >> to send a message from DSP.
> >>
> >> On 21/08/2023 18:02, Miller Puckette wrote:
> >>> The built-in objects "delay", "metro" and "pipe" use clocks in
> >>> various ways.
> >>>
> >>> On 8/21/23 18:02, Joseph Larralde wrote:
> >>>> I just read in an answer from Christof to Alexandre : "never ever
> >>>> send a Pd message directly from a perform routine ! Always use a
> >>>> clock !"
> >>
> >>
> >>
> >>
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> >
> >
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