From 0c0a35475313c6bb96c7cdf6059d245746f3843d Mon Sep 17 00:00:00 2001
From: Max Kellermann <max@musicpd.org>
Date: Fri, 28 Jun 2019 15:30:26 +0200
Subject: [PATCH] output/alsa: add a new flag "waiting" for xrun management
In DispatchSockets(), when there was not enough data, but enough for
current playback, the method would disable the "active" flag so the
next Play() call would re-enable the MultiSocketMonitor.
This was an abuse of the flag which could result in a crash
in Cancel(), because that method asserts that the period_buffer is
empty, which it may be not.
The solution is to add anther flag called "waiting" which shares some
behavior with the old flag.
---
src/output/plugins/AlsaOutputPlugin.cxx | 27 ++++++++++++++++++++-----
1 file changed, 22 insertions(+), 5 deletions(-)
diff --git a/src/output/plugins/AlsaOutputPlugin.cxx b/src/output/plugins/AlsaOutputPlugin.cxx
index 54aa6d9e0..96daac192 100644
--- a/src/output/plugins/AlsaOutputPlugin.cxx
+++ b/src/output/plugins/AlsaOutputPlugin.cxx
@@ -135,6 +135,13 @@ class AlsaOutput final
*/
bool active;
+ /**
+ * Is this output waiting for more data?
+ *
+ * Protected by #mutex.
+ */
+ bool waiting;
+
/**
* Do we need to call snd_pcm_prepare() before the next write?
* It means that we put the device to SND_PCM_STATE_SETUP by
@@ -176,7 +183,7 @@ class AlsaOutput final
Alsa::PeriodBuffer period_buffer;
/**
- * Protects #cond, #error, #active, #drain.
+ * Protects #cond, #error, #active, #waiting, #drain.
*/
mutable Mutex mutex;
@@ -248,6 +255,12 @@ private:
return active;
}
+ gcc_pure
+ bool LockIsActiveAndNotWaiting() const noexcept {
+ const std::lock_guard<Mutex> lock(mutex);
+ return active && !waiting;
+ }
+
/**
* Activate the output by registering the sockets in the
* #EventLoop. Before calling this, filling the ring buffer
@@ -260,10 +273,11 @@ private:
* was never unlocked
*/
bool Activate() noexcept {
- if (active)
+ if (active && !waiting)
return false;
active = true;
+ waiting = false;
const ScopeUnlock unlock(mutex);
defer_invalidate_sockets.Schedule();
@@ -330,6 +344,7 @@ private:
const std::lock_guard<Mutex> lock(mutex);
error = std::current_exception();
active = false;
+ waiting = false;
cond.signal();
}
@@ -684,6 +699,7 @@ AlsaOutput::Open(AudioFormat &audio_format)
period_buffer.Allocate(period_frames, out_frame_size);
active = false;
+ waiting = false;
must_prepare = false;
written = false;
error = {};
@@ -845,6 +861,7 @@ AlsaOutput::CancelInternal() noexcept
ring_buffer->reset();
active = false;
+ waiting = false;
MultiSocketMonitor::Reset();
defer_invalidate_sockets.Cancel();
@@ -930,7 +947,7 @@ AlsaOutput::Play(const void *chunk, size_t size)
std::chrono::steady_clock::duration
AlsaOutput::PrepareSockets() noexcept
{
- if (!LockIsActive()) {
+ if (!LockIsActiveAndNotWaiting()) {
ClearSocketList();
return std::chrono::steady_clock::duration(-1);
}
@@ -1001,13 +1018,13 @@ try {
{
const std::lock_guard<Mutex> lock(mutex);
- active = false;
+ waiting = true;
cond.signal();
}
/* avoid race condition: see if data has
arrived meanwhile before disabling the
- event (but after clearing the "active"
+ event (but after setting the "waiting"
flag) */
if (!CopyRingToPeriodBuffer()) {
MultiSocketMonitor::Reset();