[linux-audio-user] Re: [Jackit-devel] [Fwd: Re: Linux audio latency]

[mista.tapas at gmx.net (Florian Schmidt)]

On Sun, 03 Oct 2004 12:55:18 +0300
Sampo Savolainen <v2@xxxxxx> wrote:

> On Sun, 2004-10-03 at 08:25, Florian Schmidt wrote:
> > Starting a new jack client in itself won't produce xruns. Also,
> > cleanly shutting down a jack client will not in itself produce xruns
> > [iirc]. But it seems that many, if not most, jack apps, get some
> > part of the RT operation stuff not right. Especially start up and
> > shutdown.
> 
> Actually, that's not entirely correct. I've been talking to Paul about
> this. The xruns created by exiting clients is due to jackd having to
> rework it's internals. When doing this reordering, jackd has to lock
> the data it's modifying and sometimes (very often) there will be an
> xrun because the audio thread is waiting for the lock to be released.
> 
> In short. It's not the clients fault, it's jacks' fault.

Hi, a simple test will show you that this is not true. This program
will exit and disconnect from the jack graph after 10 seconds. I don't
get any xruns with it even a 2*32 frames. Jack's disconnection
logic might still be flawed [if paul says so]. but at least in this
case it doesn't show:

#include <jack/jack.h>
#include <iostream>

jack_client_t *client;
jack_port_t *iport;
jack_port_t *oport;

int process(jack_nframes_t frames, void *arg) {
        // actually do something
        jack_default_audio_sample_t *ibuf;
        ibuf = (jack_default_audio_sample_t*)jack_port_get_buffer(iport,
frames);

        jack_default_audio_sample_t *obuf;
        obuf = (jack_default_audio_sample_t*)jack_port_get_buffer(oport,
frames);

        for (jack_nframes_t frame = 0; frame < frames; frame++) {
                obuf[frames] = ibuf[frame];
        }
        return 0;
}

int main(int argc, char *argv[]) {
        std::cout << "client_new" << std::endl;
        client = jack_client_new("foo");

        std::cout << "port_register." << std::endl;
        iport = jack_port_register(client, "foobar_in",
		JACK_DEFAULT_AUDIO_TYPE, JackPortIsInput|JackPortIsTerminal, 0);
	oport = jack_port_register(client, "foobar_out",
		JACK_DEFAULT_AUDIO_TYPE, JackPortIsTerminal|JackPortIsOutput,
0);



        std::cout << "set_process_callback" << std::endl;
        jack_set_process_callback(client, process, 0);

        std::cout << "activate" << std::endl;
        jack_activate(client);

        jack_port_tie(iport, oport);

        std::cout << "running" << std::endl;

        // while(1) {sleep(1);};
        sleep(10);

        jack_deactivate(client);
        jack_client_close(client);
}