Bug 898478 - Have AsyncPanZoomController keep a pointer to the APZCTreeManager. r=kats

gfx/layers/composite/APZCTreeManager.cpp

@@ -118,7 +118,7 @@ APZCTreeManager::UpdatePanZoomControllerTree(CompositorParent* aCompositor,
 
         bool newApzc = (apzc == nullptr);
         if (newApzc) {
-          apzc = new AsyncPanZoomController(aLayersId, state->mController,
+          apzc = new AsyncPanZoomController(aLayersId, this, state->mController,
                                             AsyncPanZoomController::USE_GESTURE_DETECTOR);
           apzc->SetCompositorParent(aCompositor);
         } else {

gfx/layers/ipc/AsyncPanZoomController.cpp

@@ -200,6 +200,7 @@ AsyncPanZoomController::InitializeGlobalState()
 }
 
 AsyncPanZoomController::AsyncPanZoomController(uint64_t aLayersId,
+                                               APZCTreeManager* aTreeManager,
                                                GeckoContentController* aGeckoContentController,
                                                GestureBehavior aGestures)
   :  mLayersId(aLayersId),
@@ -221,7 +222,8 @@ AsyncPanZoomController::AsyncPanZoomController(uint64_t aLayersId,
      mAsyncScrollTimeoutTask(nullptr),
      mDisableNextTouchBatch(false),
      mHandlingTouchQueue(false),
-     mDelayPanning(false)
+     mDelayPanning(false),
+     mTreeManager(aTreeManager)
 {
   MOZ_COUNT_CTOR(AsyncPanZoomController);
 
@@ -262,6 +264,7 @@ AsyncPanZoomController::Destroy()
   mPrevSibling = nullptr;
   mLastChild = nullptr;
   mParent = nullptr;
+  mTreeManager = nullptr;
 }
 
 /* static */float

gfx/layers/ipc/AsyncPanZoomController.h

@@ -15,7 +15,6 @@
 #include "InputData.h"
 #include "Axis.h"
 #include "TaskThrottler.h"
-#include "mozilla/layers/APZCTreeManager.h"
 #include "gfx3DMatrix.h"
 
 #include "base/message_loop.h"
@@ -28,6 +27,7 @@ class CompositorParent;
 class GestureEventListener;
 class ContainerLayer;
 class ViewTransform;
+class APZCTreeManager;
 
 /**
  * Controller for all panning and zooming logic. Any time a user input is
@@ -73,6 +73,7 @@ public:
   static float GetTouchStartTolerance();
 
   AsyncPanZoomController(uint64_t aLayersId,
+                         APZCTreeManager* aTreeManager,
                          GeckoContentController* aController,
                          GestureBehavior aGestures = DEFAULT_GESTURES);
   ~AsyncPanZoomController();
@@ -630,6 +631,13 @@ public:
   }
 
 private:
+  // This is a raw pointer to avoid introducing a reference cycle between
+  // AsyncPanZoomController and APZCTreeManager. Since these objects don't
+  // live on the main thread, we can't use the cycle collector with them.
+  // The APZCTreeManager owns the lifetime of the APZCs, so nulling this
+  // pointer out in Destroy() will prevent accessing deleted memory.
+  APZCTreeManager* mTreeManager;
+
   nsRefPtr<AsyncPanZoomController> mLastChild;
   nsRefPtr<AsyncPanZoomController> mPrevSibling;
   nsRefPtr<AsyncPanZoomController> mParent;

gfx/tests/gtest/TestAsyncPanZoomController.cpp

@@ -45,8 +45,8 @@ class TestAPZCContainerLayer : public ContainerLayer {
 
 class TestAsyncPanZoomController : public AsyncPanZoomController {
 public:
-  TestAsyncPanZoomController(uint64_t aLayersId, MockContentController* mcc)
-    : AsyncPanZoomController(aLayersId, mcc)
+  TestAsyncPanZoomController(uint64_t aLayersId, MockContentController* aMcc)
+    : AsyncPanZoomController(aLayersId, nullptr, aMcc)
   {}
 
   void SetFrameMetrics(const FrameMetrics& metrics) {