[core] BackendScope prevent double (de-)activation

- Guards against duplicate activations by checking wether the backend of the prior scope is the same as the current ones
- Makes sure that only the most outer backend scope deactivates by tracking activation state

2 files changed, 9 insertions, 0 deletions

diff --git a/include/mbgl/renderer/backend_scope.hpp b/include/mbgl/renderer/backend_scope.hpp
index f8a258f3df..73bafc84c7 100644
--- a/include/mbgl/renderer/backend_scope.hpp
+++ b/include/mbgl/renderer/backend_scope.hpp
@@ -22,10 +22,14 @@ public:
     static bool exists();
 
 private:
+    void activate();
+    void deactivate();
+
     BackendScope* priorScope;
     BackendScope* nextScope;
     RendererBackend& backend;
     const ScopeType scopeType;
+    bool activated = false;
 };
 
 } // namespace mbgl
diff --git a/include/mbgl/renderer/renderer_backend.hpp b/include/mbgl/renderer/renderer_backend.hpp
index 9d967fd51b..a383329395 100644
--- a/include/mbgl/renderer/renderer_backend.hpp
+++ b/include/mbgl/renderer/renderer_backend.hpp
@@ -4,6 +4,7 @@
 #include <mbgl/renderer/backend_scope.hpp>
 #include <mbgl/util/image.hpp>
 #include <mbgl/util/size.hpp>
+#include <mbgl/util/util.hpp>
 
 #include <memory>
 #include <mutex>
@@ -81,4 +82,8 @@ private:
     friend class BackendScope;
 };
 
+MBGL_CONSTEXPR bool operator==(const RendererBackend& a, const RendererBackend& b) {
+    return &a == &b;
+}
+
 } // namespace mbgl