[core] send signal to RenderCustomLayer when gl context has been lost

- Prevents cleaning up of GL resources that no longer exist, resulting in a crash

include/mbgl/renderer/renderer.hpp

@@ -28,6 +28,8 @@ public:
              const optional<std::string> programCacheDir = {});
     ~Renderer();
 
+    void markContextLost();
+
     void setObserver(RendererObserver*);
 
     void render(const UpdateParameters&);

src/mbgl/renderer/layers/render_custom_layer.cpp

@@ -16,7 +16,7 @@ RenderCustomLayer::RenderCustomLayer(Immutable<style::CustomLayer::Impl> _impl)
 
 RenderCustomLayer::~RenderCustomLayer() {
     assert(BackendScope::exists());
-    if (initialized && impl().deinitializeFn) {
+    if (initialized && !contextDestroyed && impl().deinitializeFn) {
         impl().deinitializeFn(impl().context);
     }
 }

src/mbgl/renderer/layers/render_custom_layer.hpp

@@ -19,8 +19,13 @@ public:
 
     const style::CustomLayer::Impl& impl() const;
 
+    void markContextDestroyed() {
+        contextDestroyed = true;
+    };
+
 private:
     bool initialized = false;
+    bool contextDestroyed = false;
 };
 
 template <>

src/mbgl/renderer/renderer.cpp

@@ -20,6 +20,10 @@ Renderer::~Renderer() {
     impl.reset();
 }
 
+void Renderer::markContextLost() {
+    impl->markContextLost();
+}
+
 void Renderer::setObserver(RendererObserver* observer) {
     impl->setObserver(observer);
 }

src/mbgl/renderer/renderer_impl.cpp

@@ -62,6 +62,17 @@ Renderer::Impl::Impl(RendererBackend& backend_,
 
 Renderer::Impl::~Impl() {
     assert(BackendScope::exists());
+
+    if (contextLost) {
+        // Signal all RenderCustomLayers that the context was lost
+        // before cleaning up
+        for (const auto& entry : renderLayers) {
+            RenderLayer& layer = *entry.second;
+            if (layer.is<RenderCustomLayer>()) {
+                layer.as<RenderCustomLayer>()->markContextDestroyed();
+            }
+        }
+    }
 };
 
 void Renderer::Impl::setObserver(RendererObserver* observer_) {

src/mbgl/renderer/renderer_impl.hpp

@@ -39,6 +39,10 @@ public:
          const optional<std::string> programCacheDir);
     ~Impl() final;
 
+    void markContextLost() {
+        contextLost = true;
+    };
+
     void setObserver(RendererObserver*);
 
     void render(const UpdateParameters&);
@@ -100,6 +104,8 @@ private:
     std::unordered_map<std::string, std::unique_ptr<RenderSource>> renderSources;
     std::unordered_map<std::string, std::unique_ptr<RenderLayer>> renderLayers;
     RenderLight renderLight;
+
+    bool contextLost = false;
 };
 
 } // namespace mbgl