[PD] Pd 0.52-1 - frozen dsp and gui in ubuntu 20.04

[Christof Ressi]

Actually, I just remember that I fixed a very similar issue with the 
ASIO backend. However, it was a bit more nasty, because Pd would simply 
crash if the "Delay" value was too low :-) My solution was too simply 
cap the value at the hardware blocksize:

https://github.com/pure-data/pure-data/blob/3ae0388c2ba354e2b5d818c1422b7484c4a491bf/src/s_audio.c#L357

---

The problem with the Jack backend is that it caps at *Pd's* blocksize 
(64 samples) - which is often lower than the Jack buffersize. 
Consequently, the Jack callback might never have a chance to fill the 
ring buffer.

I think the solution is simple:

In /jack_open_audio()/ replace

if (advance_samples < DEFDACBLKSIZE)
     advance_samples = DEFDACBLKSIZE;

with

if (advance_samples < jack_blocksize)
     advance_samples = jack_blocksize;

@Roman: can you give this a try?

Christof

On 22.03.2022 15:39, Roman Haefeli wrote:
> On Tue, 2022-03-22 at 15:23 +0100, IOhannes m zmoelnig wrote:
>> On 3/22/22 15:06, Roman Haefeli wrote:
>>> On Tue, 2022-03-22 at 14:56 +0100, Christof Ressi wrote:
>>>>> Anyway, I can open an issue to describe that in my case DSP
>>>>> only
>>>>> works with callbacks on.
>>>>    Yes, please! The Jack backend is supposed to work regardless of
>>>> the
>>>> "callback" setting.
>>> But not regardless of the "delay (ms)" setting. If it is too low,
>>> Pd
>>> won't process audio. I don't know if there is a way to know
>>> beforehand
>>> what 'too low' is. It isn't necessarily a bug in Pd, I'd say.
>> it's probably a bug in Pd if the DSP and the GUI both freeze.
> Indeed, if the buffer is set too small, then Pd GUI freezes!
>
>  From my anecdotal testing, it looks like the critical value is
> predictable. As Christof said, the buffer cannot be smaller than JACK's
> blocksize.
>
> For instance with JACK @ 256 samples @ 44.1kHz (5.8ms):
>    - Pd works with 6ms
>    - Pd freezes with 5ms
>
> I guess the dialog could be designed in a way to set a lower boundary
> that is dependent on the detected JACK blocksize. I don't know,
> however, if Pd is able to detect the blocksize before DSP is turned on.
>
> Roman
>   
>
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