From 6613efc3b264232dd9e14e8068665e5d7a1d6b23 Mon Sep 17 00:00:00 2001
From: Persune <54422576+Gumball2415@users.noreply.github.com>
Date: Wed, 27 Dec 2023 13:59:01 +0800
Subject: [PATCH] Switch to fair mutexes to avoid UI deadlocks (#245)

Taken from https://github.com/yohhoy/yamc/blob/master/include/fair_mutex.hpp

Co-authored-by: nyanpasu64 <nyanpasu64@tuta.io>
---
 Source/SoundGen.h          | 17 +++++---
 Source/yamc/fair_mutex.hpp | 87 ++++++++++++++++++++++++++++++++++++++
 2 files changed, 98 insertions(+), 6 deletions(-)
 create mode 100644 Source/yamc/fair_mutex.hpp

diff --git a/Source/SoundGen.h b/Source/SoundGen.h
index fdcb3059..c87f5f00 100644
--- a/Source/SoundGen.h
+++ b/Source/SoundGen.h
@@ -32,6 +32,7 @@
 #include "rigtorp/SPSCQueue.h"
 #include "libsamplerate/include/samplerate.h"
 #include "utils/handle_ptr.h"
+#include "yamc/fair_mutex.hpp"
 #include <queue>		// // //
 #include "Common.h"
 #include "FamiTrackerTypes.h"
@@ -39,7 +40,6 @@
 #include <atomic>
 #include <cstdint>
 #include <memory>
-#include <mutex>
 #include <thread>
 
 const int VIBRATO_LENGTH = 256;
@@ -107,6 +107,8 @@ class CRegisterState;		// // //
 
 // CSoundGen
 
+using FairMutex = yamc::fair::mutex;
+
 class CSoundGen : IAudioCallback
 {
 public:
@@ -369,7 +371,10 @@ class CSoundGen : IAudioCallback
 
 	// Thread synchronization
 private:
-	mutable std::mutex m_csAPULock;		// // //
+	/// A fair mutex ensures that if the audio thread holds m_csAPULock,
+	/// and the UI thread is waiting for m_csAPULock,
+	/// the audio thread cannot release and reacquire m_csAPULock (starving the UI thread of access).
+	mutable FairMutex m_csAPULock;		// // //
 	mutable std::mutex m_csVisualizerWndLock;
 
 	// Handles
@@ -513,11 +518,11 @@ class CSoundGen : IAudioCallback
 	afx_msg void OnRemoveDocument(WPARAM wParam, LPARAM lParam);
 
 public:
-	std::unique_lock<std::mutex> Lock() {
-		return std::unique_lock<std::mutex>(m_csAPULock);
+	std::unique_lock<FairMutex> Lock() {
+		return std::unique_lock<FairMutex>(m_csAPULock);
 	}
 
-	std::unique_lock<std::mutex> DeferLock() {
-		return std::unique_lock<std::mutex>(m_csAPULock, std::defer_lock);
+	std::unique_lock<FairMutex> DeferLock() {
+		return std::unique_lock<FairMutex>(m_csAPULock, std::defer_lock);
 	}
 };
diff --git a/Source/yamc/fair_mutex.hpp b/Source/yamc/fair_mutex.hpp
new file mode 100644
index 00000000..b3b72abd
--- /dev/null
+++ b/Source/yamc/fair_mutex.hpp
@@ -0,0 +1,87 @@
+/*
+ * fair_mutex.hpp
+ *
+ * MIT License
+ *
+ * Copyright (c) 2017 yohhoy
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+#ifndef YAMC_FAIR_MUTEX_HPP_
+#define YAMC_FAIR_MUTEX_HPP_
+
+#include <condition_variable>
+#include <mutex>
+
+
+namespace yamc {
+
+/*
+ * fairness (FIFO locking) mutex
+ *
+ * - yamc::fair::mutex
+ * - yamc::fair::recursive_mutex
+ * - yamc::fair::timed_mutex
+ * - yamc::fair::recursive_timed_mutex
+ */
+namespace fair {
+
+class mutex {
+  std::size_t next_ = 0;
+  std::size_t curr_ = 0;
+  std::condition_variable cv_;
+  std::mutex mtx_;
+
+public:
+  mutex() = default;
+  ~mutex() = default;
+
+  mutex(const mutex&) = delete;
+  mutex& operator=(const mutex&) = delete;
+
+  void lock()
+  {
+    std::unique_lock<decltype(mtx_)> lk(mtx_);
+    const std::size_t request = next_++;
+    while (request != curr_) {
+      cv_.wait(lk);
+    }
+  }
+
+  bool try_lock()
+  {
+    std::lock_guard<decltype(mtx_)> lk(mtx_);
+    if (next_ != curr_)
+      return false;
+    ++next_;
+    return true;
+  }
+
+  void unlock()
+  {
+    std::lock_guard<decltype(mtx_)> lk(mtx_);
+    ++curr_;
+    cv_.notify_all();
+  }
+};
+
+} // namespace fair
+} // namespace yamc
+
+#endif