current jack1 (released months or years ago):

 if (snd_pcm_open (&driver->playback_handle,
                                  playback_alsa_device,
                                  SND_PCM_STREAM_PLAYBACK,
                                  SND_PCM_NONBLOCK) < 0) {
                        switch (errno) {
                        case EBUSY:
                                current_apps = discover_alsa_using_apps ();
                                if (current_apps) {
                                        jack_error ("\n\nATTENTION: The playback device \"%s\" is "
                                                    "already in use. The following applications "
                                                    " are using your soundcard(s) so you should "
                                                    " check them and stop them as necessary before "
                                                    " trying to start JACK again:\n\n%s",
                                                    playback_alsa_device,
                                                    current_apps);
                                        free (current_apps);