Bug 822115 - nglayout.debug.widget_update_flashing pref cache is not thread safe. r=mattwoodrow

gfx/layers/basic/BasicLayerManager.cpp

@@ -629,16 +629,7 @@ BasicLayerManager::EndTransactionInternal(DrawThebesLayerCallback aCallback,
 void
 BasicLayerManager::FlashWidgetUpdateArea(gfxContext *aContext)
 {
-  static bool sWidgetFlashingEnabled;
+  if (gfxPlatform::GetPlatform()->WidgetUpdateFlashing()) {
-  static bool sWidgetFlashingPrefCached = false;
-
-  if (!sWidgetFlashingPrefCached) {
-    sWidgetFlashingPrefCached = true;
-    mozilla::Preferences::AddBoolVarCache(&sWidgetFlashingEnabled,
-                                          "nglayout.debug.widget_update_flashing");
-  }
-
-  if (sWidgetFlashingEnabled) {
     float r = float(rand()) / RAND_MAX;
     float g = float(rand()) / RAND_MAX;
     float b = float(rand()) / RAND_MAX;

gfx/thebes/gfxPlatform.cpp

@@ -340,6 +340,9 @@ gfxPlatform::Init()
 
     gPlatform->mWorkAroundDriverBugs = Preferences::GetBool("gfx.work-around-driver-bugs", true);
 
+    mozilla::Preferences::AddBoolVarCache(&gPlatform->mWidgetUpdateFlashing,
+                                          "nglayout.debug.widget_update_flashing");
+
     mozilla::gl::GLContext::PlatformStartup();
 
 #ifdef MOZ_WIDGET_ANDROID

gfx/thebes/gfxPlatform.h

@@ -493,6 +493,8 @@ public:
 
     virtual int GetScreenDepth() const;
 
+    bool WidgetUpdateFlashing() const { return mWidgetUpdateFlashing; }
+
 protected:
     gfxPlatform();
     virtual ~gfxPlatform();
@@ -586,6 +588,7 @@ private:
     bool mWorkAroundDriverBugs;
 
     mozilla::RefPtr<mozilla::gfx::DrawEventRecorder> mRecorder;
+    bool mWidgetUpdateFlashing;
 };
 
 #endif /* GFX_PLATFORM_H */