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ALSA: Fix an error when priming the playback buffer.

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There was a possibility that this process could result in
snd_pcm_writei() getting stuck because the frame count is not being
clamped to the buffer size properly.
This commit is contained in:
David Reid
2026-01-13 10:22:39 +10:00
parent 92a58fae11
commit 55cdba084d
1 changed files with 44 additions and 18 deletions
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miniaudio.h
+44 -18
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@@ -29532,6 +29532,49 @@ static void ma_device_uninit__alsa(ma_device* pDevice)
ma_device_uninit_internal__alsa(pDevice, ma_device_get_backend_state__alsa(pDevice)); ma_device_uninit_internal__alsa(pDevice, ma_device_get_backend_state__alsa(pDevice));
} }
static void ma_device_prime_playback_buffer__alsa(ma_device* pDevice)
{
ma_device_state_alsa* pDeviceStateALSA = ma_device_get_backend_state__alsa(pDevice);
ma_context_state_alsa* pContextStateALSA = ma_context_get_backend_state__alsa(ma_device_get_context(pDevice));
ma_uint8 buffer[4096];
ma_uint32 bpf;
ma_uint32 framesToWrite;
ma_uint32 framesWritten;
ma_snd_pcm_sframes_t framesAvail;
if (pDeviceStateALSA->pPCMPlayback == NULL) {
return;
}
bpf = ma_get_bytes_per_frame(pDevice->playback.internalFormat, pDevice->playback.internalChannels);
framesToWrite = pDevice->playback.internalPeriodSizeInFrames * pDevice->playback.internalPeriods;
framesWritten = 0;
MA_ZERO_MEMORY(buffer, sizeof(buffer));
/* Guard against the available frame count reported by ALSA just in case we try writing too much and get stuck in snd_pcm_writei().. */
framesAvail = pContextStateALSA->snd_pcm_avail(pDeviceStateALSA->pPCMPlayback);
if (framesToWrite > framesAvail) {
framesToWrite = framesAvail;
}
while (framesWritten < framesToWrite) {
ma_uint32 framesToWriteThisIteration = sizeof(buffer) / bpf;
ma_uint32 framesRemaining = framesToWrite - framesWritten;
if (framesToWriteThisIteration > framesRemaining) {
framesToWriteThisIteration = framesRemaining;
}
/* Just a guard to ensure we don't get stuck in a loop. Should never happen in practice (would require a massive channel count). */
if (framesToWriteThisIteration == 0) {
break;
}
pContextStateALSA->snd_pcm_writei(pDeviceStateALSA->pPCMPlayback, buffer, framesToWriteThisIteration);
framesWritten += framesToWriteThisIteration;
}
}
static ma_result ma_device_start__alsa(ma_device* pDevice) static ma_result ma_device_start__alsa(ma_device* pDevice)
{ {
ma_device_state_alsa* pDeviceStateALSA = ma_device_get_backend_state__alsa(pDevice); ma_device_state_alsa* pDeviceStateALSA = ma_device_get_backend_state__alsa(pDevice);
@@ -29544,24 +29587,7 @@ static ma_result ma_device_start__alsa(ma_device* pDevice)
effectively non-blocking. effectively non-blocking.
*/ */
if (pDeviceStateALSA->pPCMPlayback != NULL) { if (pDeviceStateALSA->pPCMPlayback != NULL) {
ma_uint8 buffer[4096]; ma_device_prime_playback_buffer__alsa(pDevice);
ma_uint32 bpf = ma_get_bytes_per_frame(pDevice->playback.internalFormat, pDevice->playback.internalChannels);
ma_uint32 framesToWrite = pDevice->playback.internalPeriodSizeInFrames * pDevice->playback.internalPeriods;
ma_uint32 framesWritten = 0;
MA_ZERO_MEMORY(buffer, sizeof(buffer));
while (framesWritten < framesToWrite) {
ma_uint32 framesToWriteThisIteration = sizeof(buffer) / bpf;
/* Just a guard to ensure we don't get stuck in a loop. Should never happen in practice (would require a massive channel count). */
if (framesToWriteThisIteration == 0) {
break;
}
pContextStateALSA->snd_pcm_writei(pDeviceStateALSA->pPCMPlayback, buffer, framesToWriteThisIteration);
framesWritten += framesToWriteThisIteration;
}
} }
if (pDeviceStateALSA->pPCMCapture != NULL) { if (pDeviceStateALSA->pPCMCapture != NULL) {