From 543776d9c94763a6870511ed569df2fd7eda1577 Mon Sep 17 00:00:00 2001
From: Max Kellermann <max@musicpd.org>
Date: Fri, 28 Jun 2019 08:55:23 +0200
Subject: [PATCH 1/2] output/alsa: check PCM state before calling
snd_pcm_drain()
Apparently, if snd_pcm_drain() returns EAGAIN, it does not actually
want to be called again; the next call will snd_pcm_drain() will also
return EAGAIN, forever, even though the PCM state has meanwhile
switched to SND_PCM_STATE_SETUP. This causes a busy loop; to fix
this, we should always check snd_pcm_state() to see if draining is
really required.
---
NEWS | 1 +
src/output/plugins/AlsaOutputPlugin.cxx | 18 ++++++++++++++++++
2 files changed, 19 insertions(+)
diff --git a/NEWS b/NEWS
index b0657d4a9..1d066d290 100644
--- a/NEWS
+++ b/NEWS
@@ -4,6 +4,7 @@ ver 0.21.11 (not yet released)
* decoder
- wildmidi: log error if library initialization fails
* output
+ - alsa: fix busy loop while draining
- alsa, osx: fix distortions with DSD_U32 and DoP on 32 bit CPUs
* protocol
- fix "list" with multiple "group" levels
diff --git a/src/output/plugins/AlsaOutputPlugin.cxx b/src/output/plugins/AlsaOutputPlugin.cxx
index 8f32cf8d7..eefb7f467 100644
--- a/src/output/plugins/AlsaOutputPlugin.cxx
+++ b/src/output/plugins/AlsaOutputPlugin.cxx
@@ -774,6 +774,24 @@ AlsaOutput::DrainInternal()
don't need to drain it */
return true;
+ switch (snd_pcm_state(pcm)) {
+ case SND_PCM_STATE_PREPARED:
+ case SND_PCM_STATE_RUNNING:
+ /* these states require a call to snd_pcm_drain() */
+ break;
+
+ case SND_PCM_STATE_DRAINING:
+ /* already draining, but not yet finished; this is
+ probably a spurious epoll event, and we should wait
+ for the next one */
+ return false;
+
+ default:
+ /* all other states cannot be drained, and we're
+ done */
+ return true;
+ }
+
/* .. and finally drain the ALSA hardware buffer */
int result;
From c926021599c77b3011beec856cad535a5bedb1af Mon Sep 17 00:00:00 2001
From: Max Kellermann <max@musicpd.org>
Date: Fri, 28 Jun 2019 08:27:48 +0200
Subject: [PATCH 2/2] output/alsa: always redo DrainInternal() after writing
Draining isn't finished just because the period_buffer has run empty.
It is only finished after snd_pcm_drain() has succeeded.
---
NEWS | 1 +
src/output/plugins/AlsaOutputPlugin.cxx | 2 +-
2 files changed, 2 insertions(+), 1 deletion(-)
diff --git a/NEWS b/NEWS
index 1d066d290..542cd5d04 100644
--- a/NEWS
+++ b/NEWS
@@ -5,6 +5,7 @@ ver 0.21.11 (not yet released)
- wildmidi: log error if library initialization fails
* output
- alsa: fix busy loop while draining
+ - alsa: fix missing drain call
- alsa, osx: fix distortions with DSD_U32 and DoP on 32 bit CPUs
* protocol
- fix "list" with multiple "group" levels
diff --git a/src/output/plugins/AlsaOutputPlugin.cxx b/src/output/plugins/AlsaOutputPlugin.cxx
index eefb7f467..16832a1bc 100644
--- a/src/output/plugins/AlsaOutputPlugin.cxx
+++ b/src/output/plugins/AlsaOutputPlugin.cxx
@@ -766,7 +766,7 @@ AlsaOutput::DrainInternal()
/* need to call CopyRingToPeriodBuffer() and
WriteFromPeriodBuffer() again in the next
iteration, so don't finish the drain just yet */
- return period_buffer.IsEmpty();
+ return false;
}
if (!written)