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audio: precalculate if we can use simple copies instead of the full mixer. 

This just saves a bunch of conditionals (and an atomic get!) per iteration
of the audio thread.
main
Ryan C. Gordon 2023-09-20 09:58:27 -04:00
parent 36b0f11414
commit 23f60203a3
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GPG Key ID: FA148B892AB48044
2 changed files with 35 additions and 11 deletions
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43
src/audio/SDL_audio.c
View File

@ -137,6 +137,20 @@ static int GetDefaultSampleFramesFromFreq(const int freq)
}
}
// device should be locked when calling this.
static SDL_bool AudioDeviceCanUseSimpleCopy(SDL_AudioDevice *device)
{
SDL_assert(device != NULL);
return (
device->logical_devices && // there's a logical device
!device->logical_devices->next && // there's only _ONE_ logical device
!device->logical_devices->postmix && // there isn't a postmix callback
!SDL_AtomicGet(&device->logical_devices->paused) && // it isn't paused
device->logical_devices->bound_streams && // there's a bound stream
!device->logical_devices->bound_streams->next_binding // there's only _ONE_ bound stream.
) ? SDL_TRUE : SDL_FALSE;
}
// device management and hotplug...
@ -198,6 +212,8 @@ static void DestroyLogicalAudioDevice(SDL_LogicalAudioDevice *logdev)
SDL_UnlockMutex(stream->lock);
}
logdev->physical_device->simple_copy = AudioDeviceCanUseSimpleCopy(logdev->physical_device);
SDL_free(logdev);
}
@ -752,19 +768,12 @@ SDL_bool SDL_OutputAudioThreadIterate(SDL_AudioDevice *device)
retval = SDL_FALSE;
} else {
SDL_assert(buffer_size <= device->buffer_size); // you can ask for less, but not more.
SDL_assert(AudioDeviceCanUseSimpleCopy(device) == device->simple_copy); // make sure this hasn't gotten out of sync.
// can we do a basic copy without silencing/mixing the buffer? This is an extremely likely scenario, so we special-case it.
const SDL_bool simple_copy = device->logical_devices && // there's a logical device
!device->logical_devices->next && // there's only _ONE_ logical device
!device->logical_devices->postmix && // there isn't a postmix callback
!SDL_AtomicGet(&device->logical_devices->paused) && // it isn't paused
device->logical_devices->bound_streams && // there's a bound stream
!device->logical_devices->bound_streams->next_binding; // there's only _ONE_ bound stream.
if (simple_copy) {
if (device->simple_copy) {
SDL_LogicalAudioDevice *logdev = device->logical_devices;
SDL_AudioStream *stream = logdev->bound_streams;
const int br = GetAudioStreamDataInFormat(stream, device_buffer, buffer_size, &device->spec);
if (br < 0) { // Probably OOM. Kill the audio device; the whole thing is likely dying soon anyhow.
retval = SDL_FALSE;
@ -1423,6 +1432,7 @@ SDL_AudioDeviceID SDL_OpenAudioDevice(SDL_AudioDeviceID devid, const SDL_AudioSp
device->logical_devices->prev = logdev;
}
device->logical_devices = logdev;
device->simple_copy = AudioDeviceCanUseSimpleCopy(device);
}
SDL_UnlockMutex(device->lock);
}
@ -1437,6 +1447,7 @@ static int SetLogicalAudioDevicePauseState(SDL_AudioDeviceID devid, int value)
return -1; // ObtainLogicalAudioDevice will have set an error.
}
SDL_AtomicSet(&logdev->paused, value);
logdev->physical_device->simple_copy = AudioDeviceCanUseSimpleCopy(logdev->physical_device);
SDL_UnlockMutex(logdev->physical_device->lock);
return 0;
}
@ -1482,6 +1493,8 @@ int SDL_SetAudioPostmixCallback(SDL_AudioDeviceID devid, SDL_AudioPostmixCallbac
logdev->postmix_userdata = userdata;
}
device->simple_copy = AudioDeviceCanUseSimpleCopy(device);
SDL_UnlockMutex(device->lock);
}
return retval;
@ -1565,6 +1578,8 @@ int SDL_BindAudioStreams(SDL_AudioDeviceID devid, SDL_AudioStream **streams, int
}
}
device->simple_copy = AudioDeviceCanUseSimpleCopy(device);
SDL_UnlockMutex(device->lock);
return retval;
@ -1635,6 +1650,7 @@ void SDL_UnbindAudioStreams(SDL_AudioStream **streams, int num_streams)
stream->bound_device = NULL;
SDL_UnlockMutex(stream->lock);
if (logdev) {
logdev->physical_device->simple_copy = AudioDeviceCanUseSimpleCopy(logdev->physical_device);
SDL_UnlockMutex(logdev->physical_device->lock);
}
}
@ -1674,10 +1690,12 @@ SDL_AudioStream *SDL_OpenAudioDeviceStream(SDL_AudioDeviceID devid, const SDL_Au
SDL_AudioDevice *physdevice = logdev->physical_device;
SDL_assert(physdevice != NULL);
SDL_UnlockMutex(physdevice->lock); // we don't need to hold the lock for any of this.
const SDL_bool iscapture = physdevice->iscapture;
SDL_AtomicSet(&logdev->paused, 1); // start the device paused, to match SDL2.
physdevice->simple_copy = AudioDeviceCanUseSimpleCopy(physdevice);
SDL_UnlockMutex(physdevice->lock); // we don't need to hold the lock for any of this.
const SDL_bool iscapture = physdevice->iscapture;
SDL_AudioStream *stream = NULL;
if (iscapture) {
@ -1831,6 +1849,9 @@ void SDL_DefaultAudioDeviceChanged(SDL_AudioDevice *new_default_device)
new_default_device->logical_devices = logdev;
}
current_default_device->simple_copy = AudioDeviceCanUseSimpleCopy(current_default_device);
new_default_device->simple_copy = AudioDeviceCanUseSimpleCopy(new_default_device);
if (current_default_device->logical_devices == NULL) { // nothing left on the current physical device, close it.
// !!! FIXME: we _need_ to release this lock, but doing so can cause a race condition if someone opens a device while we're closing it.
SDL_UnlockMutex(current_default_device->lock); // can't hold the lock or the audio thread will deadlock while we WaitThread it.

3
src/audio/SDL_sysaudio.h
View File

@ -267,6 +267,9 @@ struct SDL_AudioDevice
// SDL_TRUE if this is a capture device instead of an output device
SDL_bool iscapture;
// SDL_TRUE if audio thread can skip silence/mix/convert stages and just do a basic memcpy.
SDL_bool simple_copy;
// Scratch buffers used for mixing.
Uint8 *work_buffer;
Uint8 *mix_buffer;