From 30bd0e60c7c3a60433ef16f09dbfc5d649907673 Mon Sep 17 00:00:00 2001
From: "Unknown W. Brackets" <checkins@unknownbrackets.org>
Date: Mon, 15 Feb 2021 18:04:11 -0800
Subject: [PATCH] UI: Avoid audio locks where possible.

In case of thread contention, avoid locking if not necessary.  See #13469.
---
 UI/BackgroundAudio.cpp | 43 +++++++++++++++++++++---------------------
 UI/BackgroundAudio.h   |  7 +++++--
 2 files changed, 27 insertions(+), 23 deletions(-)

diff --git a/UI/BackgroundAudio.cpp b/UI/BackgroundAudio.cpp
index 7d6ff7732e..809993d5b4 100644
--- a/UI/BackgroundAudio.cpp
+++ b/UI/BackgroundAudio.cpp
@@ -248,6 +248,7 @@ BackgroundAudio g_BackgroundAudio;
 
 BackgroundAudio::BackgroundAudio() {
 	buffer = new int[BUFSIZE]();
+	sndLoadPending_.store(false);
 }
 
 BackgroundAudio::~BackgroundAudio() {
@@ -308,21 +309,24 @@ void BackgroundAudio::Clear(bool hard) {
 		at3Reader_ = nullptr;
 	}
 	playbackOffset_ = 0;
+	sndLoadPending_ = false;
 }
 
 void BackgroundAudio::SetGame(const std::string &path) {
-	std::lock_guard<std::mutex> lock(mutex_);
 	if (path == bgGamePath_) {
 		// Do nothing
 		return;
 	}
 
-	if (path.size() == 0) {
+	std::lock_guard<std::mutex> lock(mutex_);
+	if (path.empty()) {
 		Clear(false);
+		sndLoadPending_ = false;
 		fadingOut_ = true;
 	} else {
 		Clear(true);
 		gameLastChanged_ = time_now_d();
+		sndLoadPending_ = true;
 		fadingOut_ = false;
 	}
 	volume_ = 1.0f;
@@ -397,27 +401,24 @@ int BackgroundAudio::Play() {
 void BackgroundAudio::Update() {
 	// If there's a game, and some time has passed since the selected game
 	// last changed... (to prevent crazy amount of reads when skipping through a list)
-	if (bgGamePath_.size() && (time_now_d() - gameLastChanged_ > 0.5)) {
+	if (sndLoadPending_ && (time_now_d() - gameLastChanged_ > 0.5)) {
 		std::lock_guard<std::mutex> lock(mutex_);
-		if (!at3Reader_) {
-			// Grab some audio from the current game and play it.
-			if (!g_gameInfoCache)
-				return;
+		// Already loaded somehow?  Or no game info cache?
+		if (at3Reader_ || !g_gameInfoCache)
+			return;
 
-			std::shared_ptr<GameInfo> gameInfo = g_gameInfoCache->GetInfo(NULL, bgGamePath_, GAMEINFO_WANTSND);
-			if (!gameInfo)
-				return;
-
-			if (gameInfo->pending) {
-				// Should try again shortly..
-				return;
-			}
-
-			if (gameInfo->sndFileData.size()) {
-				const std::string &data = gameInfo->sndFileData;
-				at3Reader_ = new AT3PlusReader(data);
-				lastPlaybackTime_ = 0.0;
-			}
+		// Grab some audio from the current game and play it.
+		std::shared_ptr<GameInfo> gameInfo = g_gameInfoCache->GetInfo(nullptr, bgGamePath_, GAMEINFO_WANTSND);
+		if (!gameInfo || gameInfo->pending) {
+			// Should try again shortly..
+			return;
 		}
+
+		const std::string &data = gameInfo->sndFileData;
+		if (!data.empty()) {
+			at3Reader_ = new AT3PlusReader(data);
+			lastPlaybackTime_ = 0.0;
+		}
+		sndLoadPending_ = false;
 	}
 }
diff --git a/UI/BackgroundAudio.h b/UI/BackgroundAudio.h
index fb572f52a7..d8c1ba18e6 100644
--- a/UI/BackgroundAudio.h
+++ b/UI/BackgroundAudio.h
@@ -1,7 +1,8 @@
 #pragma once
 
-#include <string>
+#include <atomic>
 #include <mutex>
+#include <string>
 #include <vector>
 
 #include "Common/UI/Root.h"
@@ -13,7 +14,6 @@ public:
 	BackgroundAudio();
 	~BackgroundAudio();
 
-	void Clear(bool hard);
 	void SetGame(const std::string &path);
 	void Update();
 	int Play();
@@ -22,12 +22,15 @@ public:
 	void PlaySFX(UI::UISound sfx);
 
 private:
+	void Clear(bool hard);
+
 	enum {
 		BUFSIZE = 44100,
 	};
 
 	std::mutex mutex_;
 	std::string bgGamePath_;
+	std::atomic<bool> sndLoadPending_;
 	int playbackOffset_ = 0;
 	AT3PlusReader *at3Reader_;
 	double gameLastChanged_ = 0.0;