[PD] DSP crashing - PD freezes.

[Dan Wilcox]

> On Feb 4, 2023, at 11:46 AM, Denis Połeć <denis.polec at gmail.com> wrote:
> 
> As far as I can tell, everything is going smoothly with the callback settings. 
> However, I still haven't quite understood what it is for.

There was some discussion, maybe a year ago, about changing the name of this option and finding ways to make it clear what it does.

Copy/paste from Christof's email replay to Romain, to which you were not in CC:

>>  Are there situations when using
>> callbacks  (on CoreAudio) bring any benefit?
> 
> With "callbacks" enabled, Pd runs directly on the audio thread. 
> Generally, this is not really recommended because Pd itself is not 
> realtime safe. Many operations block for an indeterminate amount of 
> time, e.g. any call to "malloc()", network IO, file system operations, 
> etc. The upside is that you can avoid some extra delay (see below).
> 
> With Pd's ringbuffer scheduler (= "callbacks" disabled), you can freely 
> adjust the delay according to? your needs. (The "delay" parameter 
> basically sets the size of the ringbuffer.) The price you pay is some 
> extra delay (1x the hardware buffer size). To minimize this extra delay, 
> you would set the /hardware buffer size/ as low as possible (e.g. 64 
> samples) since the audio callback does nothing but transfer a bunch of 
> samples. In this case, the extra latency would be as low as 64 samples, 
> so nothing to worry about too much.
> 
> (The "callback" option can indeed make a noticable difference when using 
> Jack with larger block sizes. Ideally you would just use the smallest 
> Jack block size possible, but this might not work well for other Jack 
> clients...)
> 
> As a side note: up until now, Pd's scheduler thread regularly goes to 
> sleep for a fixed duration, so it may wake up a bit too late. If the 
> delay setting is too low, this can lead to drop outs. With my 
> "scheduler_fix" branch, the scheduler thread waits on a semaphore and is 
> notified immediately when audio data is available. In my experience so 
> far, this allows for lower "delay" settings than before.
> 
> Christof

--------
Dan Wilcox
@danomatika <http://twitter.com/danomatika>
danomatika.com <http://danomatika.com/>
robotcowboy.com <http://robotcowboy.com/>



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