Use spin-locks for short-lived, non-recursive locking sequences

src/util/GLFont.cpp

@@ -521,7 +521,7 @@ void GLFont::drawString(const std::wstring& str, int pxHeight, float xpos, float
     if (cacheable) {
         gcCounter++;
 
-        std::lock_guard<std::mutex> lock(cache_busy);
+        std::lock_guard<SpinMutex> lock(cache_busy);
         
         if (gcCounter > GC_DRAW_COUNT_PERIOD) {
             
@@ -793,7 +793,7 @@ void GLFont::doCacheGC() {
 
 void GLFont::clearCache() {
 
-    std::lock_guard<std::mutex> lock(cache_busy);
+    std::lock_guard<SpinMutex> lock(cache_busy);
 
     std::map<std::wstring, GLFontStringCache * >::iterator cache_iter;
 

src/util/GLFont.h

@@ -13,6 +13,8 @@
 #include "wx/filename.h"
 #include "wx/stdpaths.h"
 
+#include "SpinMutex.h"
+
 class GLFontStringCache {
 public:
     GLFontStringCache();
@@ -76,9 +78,6 @@ private:
 class GLFont {
 public:
 
-
-
-
     enum Align {
         GLFONT_ALIGN_LEFT, GLFONT_ALIGN_RIGHT, GLFONT_ALIGN_CENTER, GLFONT_ALIGN_TOP, GLFONT_ALIGN_BOTTOM
     };
@@ -176,7 +175,7 @@ private:
 
     GLuint texId;
     int gcCounter;
-    std::mutex cache_busy;
+    SpinMutex cache_busy;
 
 public:
 

src/util/SpinMutex.h

@@ -0,0 +1,25 @@
+// Copyright (c) Charles J. Cliffe
+// SPDX-License-Identifier: GPL-2.0+
+
+#pragma once 
+#include <atomic>
+
+// A non-recursive Mutex implemented as a spin-lock.
+class SpinMutex {
+
+public:
+    SpinMutex() = default;
+
+    SpinMutex(const SpinMutex&) = delete;
+
+    SpinMutex& operator=(const SpinMutex&) = delete;
+
+    ~SpinMutex() { lock_state.clear(std::memory_order_release); }
+
+    void lock() { while (lock_state.test_and_set(std::memory_order_acquire)); }
+
+    void unlock() { lock_state.clear(std::memory_order_release); }
+
+private:
+    std::atomic_flag lock_state = ATOMIC_FLAG_INIT;
+};