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fix(alsa): progressive backoff retry on device busy during track skip

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When skipping tracks quickly, the previous PCM handle may not be
fully released by the kernel before the new track tries to open
the same ALSA device (snd_pcm_open fails with EBUSY).

Previous behavior: single retry after 200ms PipeWire suspend, then
immediate failure. This didn't cover our own PCM race condition.

New behavior: 4 retries with progressive backoff (50/100/200/400ms)
for both hw and plughw paths. PipeWire suspend still attempted once
upfront. Total worst-case wait: 750ms (vs 200ms before), but the
early retries at 50-100ms cover the common fast-skip case.

cc
This commit is contained in:
vicrodh committed 2026-04-06 11:23:35 -06:00
1 parent 9f2c423cd4
commit 4439070032
1 file changed
+68 -63
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crates/qbz-audio/src/alsa_backend.rs
+68 -63
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@@ -611,48 +611,50 @@ impl AlsaBackend {
log::warn!("[ALSA Backend] hw attempt failed: {}", error);
if matches!(error, super::backend::AlsaDirectError::DeviceBusy(_)) {
// PipeWire may be holding the ALSA device open.
// Suspend PipeWire sinks to release the device, then retry.
log::info!("[ALSA Backend] Device busy — suspending PipeWire sinks to release ALSA device");
if let Ok(output) = std::process::Command::new("pactl")
.args(["suspend-sink", "@DEFAULT_SINK@", "1"])
.output()
{
if output.status.success() {
log::info!("[ALSA Backend] PipeWire sink suspended, waiting for device release...");
std::thread::sleep(std::time::Duration::from_millis(200));
// Device busy: either our own previous PCM handle is still
// releasing (race on fast track skip) or PipeWire holds it.
// Retry with progressive backoff before giving up.
log::info!("[ALSA Backend] Device busy — retrying with backoff");
match super::AlsaDirectStream::new(
&hw_device,
config.sample_rate,
config.channels,
) {
Ok(stream) => {
log::info!("[ALSA Backend] ✓ Direct hw stream created after PipeWire suspend");
return Some(Ok((
stream,
super::backend::BitPerfectMode::DirectHardware,
)));
}
Err(e2) => {
log::warn!(
"[ALSA Backend] Retry after suspend also failed: {}",
e2
);
}
// Try suspending PipeWire once (covers PipeWire-held case)
let _ = std::process::Command::new("pactl")
.args(["suspend-sink", "@DEFAULT_SINK@", "1"])
.output();
let retry_delays_ms = [50, 100, 200, 400];
for (i, delay_ms) in retry_delays_ms.iter().enumerate() {
std::thread::sleep(std::time::Duration::from_millis(*delay_ms));
match super::AlsaDirectStream::new(
&hw_device,
config.sample_rate,
config.channels,
) {
Ok(stream) => {
log::info!(
"[ALSA Backend] ✓ Direct hw stream created on retry {} (after {}ms)",
i + 1,
delay_ms
);
return Some(Ok((
stream,
super::backend::BitPerfectMode::DirectHardware,
)));
}
Err(e2) => {
log::warn!(
"[ALSA Backend] Retry {}/{} failed: {}",
i + 1,
retry_delays_ms.len(),
e2
);
}
} else {
let stderr = String::from_utf8_lossy(&output.stderr);
log::warn!(
"[ALSA Backend] Failed to suspend PipeWire sink: {}",
stderr
);
}
}
// If retry failed or suspend failed, fall through to error
log::error!(
"[ALSA Backend] Cannot acquire device even after PipeWire suspend"
"[ALSA Backend] Cannot acquire device after {} retries",
retry_delays_ms.len()
);
return Some(Err(format!(
"ALSA Direct failed: {}. Device may be in use or inaccessible.",
@@ -709,35 +711,38 @@ impl AlsaBackend {
let error = super::backend::AlsaDirectError::from_alsa_error(&e);
if matches!(error, super::backend::AlsaDirectError::DeviceBusy(_)) {
log::info!("[ALSA Backend] plughw device busy — suspending PipeWire sinks to release ALSA device");
if let Ok(output) = std::process::Command::new("pactl")
log::info!("[ALSA Backend] plughw device busy — retrying with backoff");
let _ = std::process::Command::new("pactl")
.args(["suspend-sink", "@DEFAULT_SINK@", "1"])
.output()
{
if output.status.success() {
log::info!(
"[ALSA Backend] PipeWire sink suspended, retrying plughw..."
);
std::thread::sleep(std::time::Duration::from_millis(200));
.output();
match super::AlsaDirectStream::new(
&plughw_device,
config.sample_rate,
config.channels,
) {
Ok(stream) => {
log::info!("[ALSA Backend] ✓ plughw stream created after PipeWire suspend");
return Some(Ok((
stream,
super::backend::BitPerfectMode::PluginFallback,
)));
}
Err(e2) => {
log::error!(
"[ALSA Backend] plughw retry after suspend also failed: {}",
e2
);
}
let retry_delays_ms = [50, 100, 200, 400];
for (i, delay_ms) in retry_delays_ms.iter().enumerate() {
std::thread::sleep(std::time::Duration::from_millis(*delay_ms));
match super::AlsaDirectStream::new(
&plughw_device,
config.sample_rate,
config.channels,
) {
Ok(stream) => {
log::info!(
"[ALSA Backend] ✓ plughw stream created on retry {} (after {}ms)",
i + 1,
delay_ms
);
return Some(Ok((
stream,
super::backend::BitPerfectMode::PluginFallback,
)));
}
Err(e2) => {
log::warn!(
"[ALSA Backend] plughw retry {}/{} failed: {}",
i + 1,
retry_delays_ms.len(),
e2
);
}
}
}