guard against concurrent OpenGL extension loading

android/cpp/native_map_view.cpp

@@ -16,6 +16,9 @@
 #include <mbgl/platform/gl.hpp>
 #include <mbgl/util/std.hpp>
 
+
+pthread_once_t loadGLExtensions = PTHREAD_ONCE_INIT;
+
 namespace mbgl {
 namespace android {
 
@@ -296,6 +299,8 @@ void NativeMapView::terminateContext() {
     context = EGL_NO_CONTEXT;
 }
 
+void loadExtensions();
+
 void NativeMapView::createSurface(ANativeWindow *window_) {
     mbgl::Log::Debug(mbgl::Event::Android, "NativeMapView::createSurface");
 
@@ -337,7 +342,7 @@ void NativeMapView::createSurface(ANativeWindow *window_) {
         }
         log_gl_string(GL_EXTENSIONS, "Extensions");
 
-        loadExtensions();
+        pthread_once(&loadGLExtensions, loadExtensions);
 
         if (!eglMakeCurrent(display, EGL_NO_SURFACE, EGL_NO_SURFACE, EGL_NO_CONTEXT)) {
             mbgl::Log::Error(mbgl::Event::OpenGL,
@@ -553,7 +558,6 @@ EGLConfig NativeMapView::chooseConfig(const EGLConfig configs[], EGLint numConfi
 
     // Sort the configs to find the best one
     configList.sort();
-    usingDepth24 = std::get<1>(configList.front()) == Format24Depth8Stencil;
     bool isConformant = !std::get<2>(configList.front());
     bool isCaveat = std::get<3>(configList.front());
     int configNum = std::get<4>(configList.front());
@@ -588,7 +592,7 @@ void NativeMapView::start() {
     map.start(true);
 }
 
-void NativeMapView::loadExtensions() {
+void loadExtensions() {
     const GLubyte *str = glGetString(GL_EXTENSIONS);
     if (str == nullptr) {
         mbgl::Log::Error(mbgl::Event::OpenGL, "glGetString(GL_EXTENSIONS) returned error %d",
@@ -620,12 +624,7 @@ void NativeMapView::loadExtensions() {
     }
 
     if (extensions.find("GL_OES_depth24") != std::string::npos) {
-        mbgl::Log::Info(mbgl::Event::OpenGL, "Using GL_OES_depth24.");
-        if (usingDepth24) {
-            gl::isDepth24Supported = true;
-        } else {
-            mbgl::Log::Info(mbgl::Event::OpenGL, "Preferring 16 bit depth.");
-        }
+        gl::isDepth24Supported = true;
     }
 
     if (extensions.find("GL_KHR_debug") != std::string::npos) {

include/mbgl/android/native_map_view.hpp

@@ -54,8 +54,6 @@ public:
 private:
     EGLConfig chooseConfig(const EGLConfig configs[], EGLint numConfigs);
 
-    void loadExtensions();
-
     bool inEmulator();
 
 private:
@@ -80,8 +78,6 @@ private:
 
     bool firstTime = false;
 
-    bool usingDepth24 = false;
-
     bool fpsEnabled = false;
     double fps = 0.0;
 };

include/mbgl/platform/default/headless_view.hpp

@@ -60,6 +60,8 @@ private:
     GLXPbuffer glxPbuffer = 0;
 #endif
 
+    bool extensionsLoaded = false;
+
     GLuint fbo = 0;
     GLuint fboDepthStencil = 0;
     GLuint fboColor = 0;

platform/default/glfw_view.cpp

@@ -2,6 +2,8 @@
 #include <mbgl/platform/gl.hpp>
 #include <mbgl/platform/log.hpp>
 
+pthread_once_t loadGLExtensions = PTHREAD_ONCE_INIT;
+
 GLFWView::GLFWView(bool fullscreen_) : fullscreen(fullscreen_) {
 #ifdef NVIDIA
     glDiscardFramebufferEXT = reinterpret_cast<PFNGLDISCARDFRAMEBUFFEREXTPROC>(glfwGetProcAddress("glDiscardFramebufferEXT"));
@@ -71,8 +73,8 @@ void GLFWView::initialize(mbgl::Map *map_) {
     glfwSetScrollCallback(window, onScroll);
     glfwSetKeyCallback(window, onKey);
 
-    const std::string extensions = reinterpret_cast<const char *>(MBGL_CHECK_ERROR(glGetString(GL_EXTENSIONS)));
-    {
+    pthread_once(&loadGLExtensions, [] {
+        const std::string extensions = reinterpret_cast<const char *>(MBGL_CHECK_ERROR(glGetString(GL_EXTENSIONS)));
         using namespace mbgl;
 
         if (extensions.find("GL_KHR_debug") != std::string::npos) {
@@ -152,7 +154,7 @@ void GLFWView::initialize(mbgl::Map *map_) {
         // Require packed depth stencil
         gl::isPackedDepthStencilSupported = true;
         gl::isDepth24Supported = true;
-    }
+    });
 
     glfwMakeContextCurrent(nullptr);
 }

platform/default/headless_view.cpp

@@ -10,6 +10,8 @@
 #include <cstring>
 #include <cassert>
 
+pthread_once_t loadGLExtensions = PTHREAD_ONCE_INIT;
+
 #ifdef MBGL_USE_CGL
 #include <CoreFoundation/CoreFoundation.h>
 
@@ -48,10 +50,18 @@ HeadlessView::HeadlessView(std::shared_ptr<HeadlessDisplay> display)
 }
 
 void HeadlessView::loadExtensions() {
-    activate();
-    const char *extensionPtr = reinterpret_cast<const char *>(MBGL_CHECK_ERROR(glGetString(GL_EXTENSIONS)));
+    if (extensionsLoaded) {
+        return;
+    }
 
-    if (extensionPtr) {
+    activate();
+
+    pthread_once(&loadGLExtensions, [] {
+        const char *extensionPtr = reinterpret_cast<const char *>(MBGL_CHECK_ERROR(glGetString(GL_EXTENSIONS)));
+
+        if (!extensionPtr) {
+            return;
+        }
         const std::string extensions = extensionPtr;
 
 #ifdef MBGL_USE_CGL
@@ -78,12 +88,14 @@ void HeadlessView::loadExtensions() {
             assert(gl::IsVertexArray != nullptr);
         }
 #endif
-    }
+    });
 
     // HeadlessView requires packed depth stencil
     gl::isPackedDepthStencilSupported = true;
     gl::isDepth24Supported = true;
 
+    extensionsLoaded = true;
+
     deactivate();
 }
 

platform/ios/MGLMapView.mm

@@ -37,6 +37,7 @@ const std::string &defaultCacheDatabase() {
     return path;
 }
 
+static dispatch_once_t loadGLExtensions;
 
 extern NSString *const MGLStyleKeyGeneric;
 extern NSString *const MGLStyleKeyFill;
@@ -213,8 +214,9 @@ mbgl::DefaultFileSource *mbglFileSource = nullptr;
 
     // load extensions
     //
-    const std::string extensions = (char *)glGetString(GL_EXTENSIONS);
-    {
+    dispatch_once(&loadGLExtensions, ^{
+        const std::string extensions = (char *)glGetString(GL_EXTENSIONS);
+
         using namespace mbgl;
 
         if (extensions.find("GL_OES_vertex_array_object") != std::string::npos) {
@@ -231,7 +233,7 @@ mbgl::DefaultFileSource *mbglFileSource = nullptr;
         if (extensions.find("GL_OES_depth24") != std::string::npos) {
             gl::isDepth24Supported = YES;
         }
-    }
+    });
 
     // setup mbgl map
     //