From a10a3ecbaccbbbdc31be5898cbc9a88ab2d8b872 Mon Sep 17 00:00:00 2001
From: Scott Mansell <phiren@gmail.com>
Date: Wed, 30 Sep 2015 00:51:34 +1300
Subject: [PATCH] ALSA: Don't block on Clear() call.

snd_pcm_writei() is meant to block block until all samples are written,
but apparently in some situations it can block for much longer, prehaps
even a infinite time, in the case of virtual machine FifoCI runs in.

Because it grabed a mutex before blocking, it could also block the
Clear() call for an infinite length of time, blocking dolphin's emu
thread.

snd_pcm_writei() also takes 10-15 seconds if you run dolphin under GDB
and can randomly take 5 or so seconds during normal usage.

By moving all the pause code to the ALSA thread, Clear() no-longer
blocks and everyone keeps their sanity.
---
 Source/Core/AudioCommon/AlsaSoundStream.cpp | 46 ++++++++++-----------
 Source/Core/AudioCommon/AlsaSoundStream.h   |  1 +
 2 files changed, 24 insertions(+), 23 deletions(-)

diff --git a/Source/Core/AudioCommon/AlsaSoundStream.cpp b/Source/Core/AudioCommon/AlsaSoundStream.cpp
index 10b05e844109..19a21acf6653 100644
--- a/Source/Core/AudioCommon/AlsaSoundStream.cpp
+++ b/Source/Core/AudioCommon/AlsaSoundStream.cpp
@@ -48,21 +48,31 @@ void AlsaSound::Update()
 void AlsaSound::SoundLoop()
 {
 	Common::SetCurrentThreadName("Audio thread - alsa");
-	while (m_thread_status.load() == ALSAThreadStatus::RUNNING)
+	while (m_thread_status.load() != ALSAThreadStatus::STOPPING)
 	{
-		std::unique_lock<std::mutex> lock(cv_m);
-		cv.wait(lock, [this]{return !m_muted || m_thread_status.load() != ALSAThreadStatus::RUNNING;});
-
-		m_mixer->Mix(mix_buffer, frames_to_deliver);
-		int rc = snd_pcm_writei(handle, mix_buffer, frames_to_deliver);
-		if (rc == -EPIPE)
+		while (m_thread_status.load() == ALSAThreadStatus::RUNNING)
 		{
-			// Underrun
-			snd_pcm_prepare(handle);
+			m_mixer->Mix(mix_buffer, frames_to_deliver);
+			int rc = snd_pcm_writei(handle, mix_buffer, frames_to_deliver);
+			if (rc == -EPIPE)
+			{
+				// Underrun
+				snd_pcm_prepare(handle);
+			}
+			else if (rc < 0)
+			{
+				ERROR_LOG(AUDIO, "writei fail: %s", snd_strerror(rc));
+			}
 		}
-		else if (rc < 0)
+		if (m_thread_status.load() == ALSAThreadStatus::PAUSED)
 		{
-			ERROR_LOG(AUDIO, "writei fail: %s", snd_strerror(rc));
+			snd_pcm_drop(handle); // Stop sound output
+
+			// Block until thread status changes.
+			std::unique_lock<std::mutex> lock(cv_m);
+			cv.wait(lock, [this]{ return m_thread_status.load() != ALSAThreadStatus::PAUSED; });
+
+			snd_pcm_prepare(handle); // resume sound output
 		}
 	}
 	AlsaShutdown();
@@ -73,18 +83,8 @@ void AlsaSound::SoundLoop()
 void AlsaSound::Clear(bool muted)
 {
 	m_muted = muted;
-	if (m_muted)
-	{
-		std::lock_guard<std::mutex> lock(cv_m);
-		snd_pcm_drop(handle);
-	}
-	else
-	{
-		std::unique_lock<std::mutex> lock(cv_m);
-		snd_pcm_prepare(handle);
-		lock.unlock();
-		cv.notify_one();
-	}
+	m_thread_status.store(muted ? ALSAThreadStatus::PAUSED : ALSAThreadStatus::RUNNING);
+	cv.notify_one(); // Notify thread that status has changed
 }
 
 bool AlsaSound::AlsaInit()
diff --git a/Source/Core/AudioCommon/AlsaSoundStream.h b/Source/Core/AudioCommon/AlsaSoundStream.h
index 721fbbd43bf7..915316f279ee 100644
--- a/Source/Core/AudioCommon/AlsaSoundStream.h
+++ b/Source/Core/AudioCommon/AlsaSoundStream.h
@@ -46,6 +46,7 @@ class AlsaSound final : public SoundStream
 	enum class ALSAThreadStatus
 	{
 		RUNNING,
+		PAUSED,
 		STOPPING,
 		STOPPED,
 	};