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

[Miller Puckette]

Hi Joseph -

If you send a message from within the DSP chain that causes the chain 
itself to be rebuilt it will crash Pd.  That's not a thread problem, but 
a (sort of) reentrancy problem.  If you're the only user of your object 
you can simply avoid doing that, but if you're publishing your object it 
might bite someone else.

The built-in objects "delay", "metro" and "pipe" use clocks in various ways.

cheers

Miller

On 8/21/23 18:02, Joseph Larralde wrote:
> Howdy,
>
> 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 !"
> But I never took the time to deeply understand Pd's inner working and 
> am not sure why it is bad practice.
> Not sure what could be the consequences of doing this, but it might 
> explain a random bug I've been experiencing with one of my externals.
> I wrote a couple of plugins with juce so I'm aware of the most basic 
> good lock-free programming practices in C++ (which seems to boil down 
> to : use atomic variables in C++, or a lock-free queue if needed).
> Could Christof's advice be related to threading issues ?
> I thought I'd read somewhere that everything was running on the same 
> thread in Pd (at least the "backend", maybe not the GUI), but please 
> correct me if I'm wrong.
> Also, I'm having a hard time finding any doc about clocks, is there a 
> known object that uses them that I could take as an example ?
> Sorry if this has been brought up before (which is probably the case), 
> and thanks in advance for your enlightenments.
>
> Cheers,
>
> Joseph Larralde
> -- 
> freelance developer
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