guard against concurrent OpenGL extension loading

3 files changed, 25 insertions, 9 deletions

diff --git a/platform/default/glfw_view.cpp b/platform/default/glfw_view.cpp
index 865636aebf..6d23a51ffb 100644
--- a/platform/default/glfw_view.cpp
+++ b/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);
 }
diff --git a/platform/default/headless_view.cpp b/platform/default/headless_view.cpp
index a3128234ea..5f41994c27 100644
--- a/platform/default/headless_view.cpp
+++ b/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() {
+    if (extensionsLoaded) {
+        return;
+    }
+
     activate();
-    const char *extensionPtr = reinterpret_cast<const char *>(MBGL_CHECK_ERROR(glGetString(GL_EXTENSIONS)));
 
-    if (extensionPtr) {
+    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();
 }
 
diff --git a/platform/ios/MGLMapView.mm b/platform/ios/MGLMapView.mm
index b1932737b7..45c96e7c3b 100644
--- a/platform/ios/MGLMapView.mm
+++ b/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
     //