[Jack-Devel] Avoiding spinlocks in a parallel sequencer

[Johannes Lorenz]

Hi,

> I try to understand your plan:
> 
> simple data flow example:
> 
> zynaddsubfx_1_output
> 
>           V
> sequencer_client_1_input
> 
>           V
> sequencer_input_ringbuffer
> 
>           V
> (sequencer processing stuff)
> 
>           V
> sequencer_output_ringbuffer
> 
>           V
> sequencer_client_output
> 
>           V
> system_client_input(hardware output)

Your picture is indeed correct. To add some more examples:

  * Something like this is also possible

        sequencer_input_ringbuffer_1     sequencer_input_ringbuffer_2
                V                                V
        plus (i.e. addition of sound-waves)
                V
        plus_effect_ringbuffer

  * The part that you labeled "(sequencer processing stuff)" might be filled with:

                V
        peak_controller_effect        some lfo generator
                V (lfo)                       V (lfo)
        zynaddsubfx_2_volume_input    zynaddsubfx_2_filter_freq_input
                V
        (zynaddsubfx_2)
                V
        zynaddsubfx_2_output
                V
        sequencer_client_2_input
                V

> Maybe also what you envision to happen in which thread or which
> callback?

Let's take the second example. zynaddsubfx itself is in another process, so we don't need to run this at all. For feeding each ringbuffer from zyn, I planned to use a separate jack client. E.g., if process() of sequencer_client_1_input is being called, it simply copies "nframes" into sequencer_input_ringbuffer.

Everything that now remains (e.g. lfo generator, peak_controller_effect, sending input to zynaddsubfx_2) is done by a process() callback of sequencer_client_output. I call this one the master jack client.

About the problem:

A point where I think spinlocks can't be avoided would be, e.g., reading from sequencer_output_ringbuffer. The sequencer's master jack client would need to do that in process(), but it can not guess when the ringbuffer reader from sequencer_client_2_input has even started to feed the ringbuffer.

> Do you want to do some signal processing in your sequencer or would it
> be ok to delegate this to other jack clients? (may be easier)

Hopefully you got it from the explenations above: the master jack client would do this right now, as I planned. Other ideas will be fine, too. Though, I guess, for "some lfo generator", e.g., a separate jack client would be overkill, as this generator simply does, e.g., f(x) = sin(x).