From f8f95e2dbd73d0d43211136e50a8d640f145872c Mon Sep 17 00:00:00 2001
From: Max Kellermann <max@duempel.org>
Date: Wed, 6 Nov 2013 23:47:30 +0100
Subject: OutputControl: reduce the number of OutputThread wakeups

Wake up the OutputThread only if it hasn't already been woken up and
if it isn't already in the playback loop.
---
 src/OutputControl.cxx  |  5 ++++-
 src/OutputInit.cxx     |  2 ++
 src/OutputInternal.hxx | 15 +++++++++++++++
 src/OutputThread.cxx   | 10 +++++++++-
 4 files changed, 30 insertions(+), 2 deletions(-)

diff --git a/src/OutputControl.cxx b/src/OutputControl.cxx
index 648705908..553507a2a 100644
--- a/src/OutputControl.cxx
+++ b/src/OutputControl.cxx
@@ -248,8 +248,11 @@ audio_output_play(struct audio_output *ao)
 
 	assert(ao->allow_play);
 
-	if (audio_output_is_open(ao))
+	if (audio_output_is_open(ao) && !ao->in_playback_loop &&
+	    !ao->woken_for_play) {
+		ao->woken_for_play = true;
 		ao->cond.signal();
+	}
 }
 
 void audio_output_pause(struct audio_output *ao)
diff --git a/src/OutputInit.cxx b/src/OutputInit.cxx
index 49b5d68b9..28eba1ab2 100644
--- a/src/OutputInit.cxx
+++ b/src/OutputInit.cxx
@@ -171,6 +171,8 @@ ao_base_init(struct audio_output *ao,
 	ao->open = false;
 	ao->pause = false;
 	ao->allow_play = true;
+	ao->in_playback_loop = false;
+	ao->woken_for_play = false;
 	ao->fail_timer = nullptr;
 
 	/* set up the filter chain */
diff --git a/src/OutputInternal.hxx b/src/OutputInternal.hxx
index 2b3136f94..c07cdf856 100644
--- a/src/OutputInternal.hxx
+++ b/src/OutputInternal.hxx
@@ -127,6 +127,21 @@ struct audio_output {
 	 */
 	bool allow_play;
 
+	/**
+	 * True while the OutputThread is inside ao_play().  This
+	 * means the PlayerThread does not need to wake up the
+	 * OutputThread when new chunks are added to the MusicPipe,
+	 * because the OutputThread is already watching that.
+	 */
+	bool in_playback_loop;
+
+	/**
+	 * Has the OutputThread been woken up to play more chunks?
+	 * This is set by audio_output_play() and reset by ao_play()
+	 * to reduce the number of duplicate wakeups.
+	 */
+	bool woken_for_play;
+
 	/**
 	 * If not nullptr, the device has failed, and this timer is used
 	 * to estimate how long it should stay disabled (unless
diff --git a/src/OutputThread.cxx b/src/OutputThread.cxx
index c6f2e4d30..30d3ba30f 100644
--- a/src/OutputThread.cxx
+++ b/src/OutputThread.cxx
@@ -510,6 +510,9 @@ ao_play(struct audio_output *ao)
 
 	ao->chunk_finished = false;
 
+	assert(!ao->in_playback_loop);
+	ao->in_playback_loop = true;
+
 	while (chunk != nullptr && ao->command == AO_COMMAND_NONE) {
 		assert(!ao->chunk_finished);
 
@@ -525,6 +528,9 @@ ao_play(struct audio_output *ao)
 		chunk = chunk->next;
 	}
 
+	assert(ao->in_playback_loop);
+	ao->in_playback_loop = false;
+
 	ao->chunk_finished = true;
 
 	ao->mutex.unlock();
@@ -656,8 +662,10 @@ audio_output_task(void *arg)
 			   chunks in the pipe */
 			continue;
 
-		if (ao->command == AO_COMMAND_NONE)
+		if (ao->command == AO_COMMAND_NONE) {
+			ao->woken_for_play = false;
 			ao->cond.wait(ao->mutex);
+		}
 	}
 }
 
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