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audio: Mark disconnected default devices as "zombies".

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Zombie devices just sit there doing nothing until a new default device
is chosen, and then they migrate all their logical devices before being
destroyed.

This lets the system deal with the likely outcome of a USB headset being
the default audio device, and when its cable is yanked out, the backend
will likely announce this _before_ it chooses a new default (or, perhaps,
the only device in the system got yanked out and there _isn't_ a new
default to be had until the user plugs the cable back in).

This lets the audio device hold on without disturbing the app until it can
seamlessly migrate audio, and it also means the backend does not have to
be careful in how it announces device events, since SDL will manage the
time between a device loss and its replacement.

Note that this _only_ applies to things opened as the default device
(SDL_AUDIO_DEVICE_DEFAULT_OUTPUT, etc). If those USB headphones are the
default, and one SDL_OpenAudioDevice() call asked for them specifically and
the other just said "give me the system default," the explicitly requested
open will get a device-lost notification immediately. The other open will
live on as a zombie until it can migrate to the new default.

This drops the complexity of the PulseAudio hotplug thread dramatically,
back to what it was previously, since it no longer needs to fight against
Pulse's asychronous nature, but just report device disconnects and new
default choices as they arrive.

loopwave has been updated to not check for device removals anymore; since
it opens the default device, this is now managed for it; it no longer
needs to close and reopen a device, and as far as it knows, the device
is never lost in the first place.
This commit is contained in:
Ryan C. Gordon 2023-06-23 21:50:24 -04:00
parent cdd2ba81de
commit fe1daf6fb5
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GPG key ID: FA148B892AB48044
4 changed files with 111 additions and 143 deletions
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14
test/loopwave.c
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@ -103,14 +103,6 @@ open_audio(void)
SDL_SetAudioStreamGetCallback(stream, fillerup, NULL);
}
#ifndef __EMSCRIPTEN__
static void reopen_audio(void)
{
close_audio();
open_audio();
}
#endif
static int done = 0;
@ -191,8 +183,6 @@ int main(int argc, char *argv[])
open_audio();
SDL_FlushEvents(SDL_EVENT_AUDIO_DEVICE_ADDED, SDL_EVENT_AUDIO_DEVICE_REMOVED);
#ifdef __EMSCRIPTEN__
emscripten_set_main_loop(loop, 0, 1);
#else
@ -203,10 +193,6 @@ int main(int argc, char *argv[])
if (event.type == SDL_EVENT_QUIT) {
done = 1;
}
if ((event.type == SDL_EVENT_AUDIO_DEVICE_ADDED && !event.adevice.iscapture) ||
(event.type == SDL_EVENT_AUDIO_DEVICE_REMOVED && !event.adevice.iscapture && event.adevice.which == device)) {
reopen_audio();
}
}
SDL_Delay(100);