fix(core): make headless OpenGL display singletons thread-safe (#4332)

CHANGELOG.md

@@ -29,6 +29,7 @@
 ### 🐞 Bug fixes
 
 - *...Add new stuff here...*
+- [core] Fix thread-unsafe headless OpenGL display singleton initialization [#4332](https://github.com/maplibre/maplibre-native/pull/4332)
 - [macos] Fix `mlt-cpp` and `mbgl-vendor-icu` not being included in the amalgamation
 - [core] Fix memory access violation exception in vector_tile_data.cpp [#632](https://github.com/maplibre/maplibre-native/pull/632)
 - [iOS] Fix a bug where the compass was determined to be misplaced when hidden [#498](https://github.com/maplibre/maplibre-native/pull/498).

platform/linux/src/headless_backend_egl.cpp

@@ -6,6 +6,7 @@
 #include <EGL/egl.h>
 
 #include <cassert>
+#include <memory>
 #include <sstream>
 
 namespace mbgl {
@@ -51,12 +52,9 @@ public:
     ~EGLDisplayConfig() { eglTerminate(display); }
 
     static std::shared_ptr<const EGLDisplayConfig> create() {
-        static std::weak_ptr<const EGLDisplayConfig> instance;
-        auto shared = instance.lock();
-        if (!shared) {
-            instance = shared = std::make_shared<EGLDisplayConfig>(Key{});
-        }
-        return shared;
+        // C++11 magic static guarantees thread-safe one-shot initialization.
+        static const auto instance = std::make_shared<EGLDisplayConfig>(Key{});
+        return instance;
     }
 
 public:

platform/linux/src/headless_backend_glx.cpp

@@ -3,6 +3,7 @@
 #include <mbgl/util/logging.hpp>
 
 #include <cassert>
+#include <memory>
 
 #ifdef CI_BUILD
 #include <chrono>
@@ -80,12 +81,9 @@ public:
     }
 
     static std::shared_ptr<const GLXDisplayConfig> create() {
-        static std::weak_ptr<const GLXDisplayConfig> instance;
-        auto shared = instance.lock();
-        if (!shared) {
-            instance = shared = std::make_shared<GLXDisplayConfig>(Key{});
-        }
-        return shared;
+        // C++11 magic static guarantees thread-safe one-shot initialization.
+        static const auto instance = std::make_shared<GLXDisplayConfig>(Key{});
+        return instance;
     }
 
 public:

platform/windows/src/headless_backend_egl.cpp

@@ -6,6 +6,7 @@
 #include <EGL/egl.h>
 
 #include <cassert>
+#include <memory>
 #include <sstream>
 #include <iomanip>
 
@@ -53,12 +54,9 @@ public:
     ~EGLDisplayConfig() { eglTerminate(display); }
 
     static std::shared_ptr<const EGLDisplayConfig> create() {
-        static std::weak_ptr<const EGLDisplayConfig> instance;
-        auto shared = instance.lock();
-        if (!shared) {
-            instance = shared = std::make_shared<EGLDisplayConfig>(Key{});
-        }
-        return shared;
+        // C++11 magic static guarantees thread-safe one-shot initialization.
+        static const auto instance = std::make_shared<EGLDisplayConfig>(Key{});
+        return instance;
     }
 
 public: