[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

1 files changed, 113 insertions, 0 deletions

diff --git a/test/renderer/backend_scope.test.cpp b/test/renderer/backend_scope.test.cpp
new file mode 100644
index 0000000000..6afd8f12ed
--- /dev/null
+++ b/test/renderer/backend_scope.test.cpp
@@ -0,0 +1,113 @@
+#include <mbgl/test/util.hpp>
+
+#include <mbgl/map/backend.hpp>
+#include <mbgl/map/backend_scope.hpp>
+
+#include <functional>
+
+using namespace mbgl;
+
+class StubBackend: public Backend {
+public:
+
+    void activate() override {
+        if (activateFunction) activateFunction();
+    }
+
+    void deactivate() override {
+        if (deactivateFunction) deactivateFunction();
+    }
+
+    void updateAssumedState() override {
+        if (updateAssumedStateFunction) updateAssumedStateFunction();
+    }
+
+    void invalidate() override {}
+
+    gl::ProcAddress initializeExtension(const char* ext) override {
+        if (initializeExtensionFunction) {
+            return initializeExtensionFunction(ext);
+        } else {
+            return {};
+        }
+    }
+
+    std::function<void ()> activateFunction;
+    std::function<void ()> deactivateFunction;
+    std::function<void ()> updateAssumedStateFunction;
+    std::function<gl::ProcAddress (const char*)> initializeExtensionFunction;
+};
+
+// A scope should activate on construction
+// and deactivate on descruction (going out
+// of scope)
+TEST(BackendScope, SingleScope) {
+    bool activated;
+    bool deactivated;
+
+    StubBackend backend;
+    backend.activateFunction = [&] { activated = true; };
+    backend.deactivateFunction = [&] { deactivated = true; };
+
+    {
+        BackendScope test { backend };
+    }
+
+    ASSERT_TRUE(activated);
+    ASSERT_TRUE(deactivated);
+}
+
+// With nested scopes, only the outer scope
+// should activate/deactivate
+TEST(BackendScope, NestedScopes) {
+    int activated = 0;
+    int deactivated = 0;
+
+    StubBackend backend;
+    backend.activateFunction = [&] { activated++; };
+    backend.deactivateFunction = [&] { deactivated++; };
+
+    {
+        BackendScope outer { backend };
+        ASSERT_EQ(1, activated);
+        {
+            BackendScope inner { backend };
+            ASSERT_EQ(1, activated);
+        }
+        ASSERT_EQ(0, deactivated);
+    }
+
+    ASSERT_EQ(1, deactivated);
+}
+
+// With chained scopes, where scopes have
+// different backends, the scopes should each
+// activate the scope on entering and de-activating
+// on leaving the scope
+TEST(BackendScope, ChainedScopes) {
+    bool activatedA = false;
+    bool activatedB = false;
+    
+    StubBackend backendA;
+    backendA.activateFunction = [&] { activatedA = true; };
+    backendA.deactivateFunction = [&] { activatedA = false; };
+    
+    StubBackend backendB;
+    backendB.activateFunction = [&] { activatedB = true; };
+    backendB.deactivateFunction = [&] { activatedB = false; };
+    
+    {
+        BackendScope scopeA { backendA };
+        ASSERT_TRUE(activatedA);
+        {
+            BackendScope scopeB { backendB };
+            ASSERT_FALSE(activatedA);
+            ASSERT_TRUE(activatedB);
+        }
+        ASSERT_FALSE(activatedB);
+        ASSERT_TRUE(activatedA);
+    }
+    
+    ASSERT_FALSE(activatedA);
+    ASSERT_FALSE(activatedB);
+}