Bug 1447299 - Have the APZCTreeManager keep a pointer to the sampler. r=botond

MozReview-Commit-ID: GiITwCDuWAW

--HG--
extra : rebase_source : 13a288785c0c3d7d0374e253f4211bfe7c5540bc

gfx/layers/apz/src/APZCTreeManager.cpp

@@ -21,6 +21,7 @@
 #include "mozilla/gfx/GPUParent.h"      // for GPUParent
 #include "mozilla/gfx/Logging.h"        // for gfx::TreeLog
 #include "mozilla/gfx/Point.h"          // for Point
+#include "mozilla/layers/APZSampler.h"  // for APZSampler
 #include "mozilla/layers/APZThreadUtils.h"  // for AssertOnControllerThread, etc
 #include "mozilla/layers/AsyncCompositionManager.h" // for ViewTransform
 #include "mozilla/layers/AsyncDragMetrics.h" // for AsyncDragMetrics
@@ -224,6 +225,7 @@ private:
 APZCTreeManager::APZCTreeManager(LayersId aRootLayersId)
     : mInputQueue(new InputQueue()),
       mRootLayersId(aRootLayersId),
+      mSampler(nullptr),
       mTreeLock("APZCTreeLock"),
       mHitResultForInputBlock(CompositorHitTestInfo::eInvisibleToHitTest),
       mRetainedTouchIdentifier(-1),
@@ -246,6 +248,14 @@ APZCTreeManager::APZCTreeManager(LayersId aRootLayersId)
 
 APZCTreeManager::~APZCTreeManager() = default;
 
+void
+APZCTreeManager::SetSampler(APZSampler* aSampler)
+{
+  // We're either setting the sampler or clearing it
+  MOZ_ASSERT((mSampler == nullptr) != (aSampler == nullptr));
+  mSampler = aSampler;
+}
+
 void
 APZCTreeManager::NotifyLayerTreeAdopted(LayersId aLayersId,
                                         const RefPtr<APZCTreeManager>& aOldApzcTreeManager)

gfx/layers/apz/src/APZCTreeManager.h

@@ -45,6 +45,7 @@ namespace layers {
 class Layer;
 class AsyncPanZoomController;
 class APZCTreeManagerParent;
+class APZSampler;
 class CompositorBridgeParent;
 class OverscrollHandoffChain;
 struct OverscrollHandoffState;
@@ -116,6 +117,8 @@ class APZCTreeManager : public IAPZCTreeManager
 public:
   explicit APZCTreeManager(LayersId aRootLayersId);
 
+  void SetSampler(APZSampler* aSampler);
+
   /**
    * Notifies this APZCTreeManager that the associated compositor is now
    * responsible for managing another layers id, which got moved over from
@@ -691,6 +694,13 @@ private:
   /* Layers id for the root CompositorBridgeParent that owns this APZCTreeManager. */
   LayersId mRootLayersId;
 
+  /* Pointer to the APZSampler instance that is bound to this APZCTreeManager.
+   * The sampler has a RefPtr to this class, and this non-owning raw pointer
+   * back to the APZSampler is nulled out in the sampler's destructor, so this
+   * pointer should always be valid.
+   */
+  APZSampler* MOZ_NON_OWNING_REF mSampler;
+
   /* Whenever walking or mutating the tree rooted at mRootNode, mTreeLock must be held.
    * This lock does not need to be held while manipulating a single APZC instance in
    * isolation (that is, if its tree pointers are not being accessed or mutated). The

gfx/layers/apz/src/APZSampler.cpp

@@ -18,9 +18,14 @@ namespace layers {
 APZSampler::APZSampler(const RefPtr<APZCTreeManager>& aApz)
   : mApz(aApz)
 {
+  MOZ_ASSERT(aApz);
+  mApz->SetSampler(this);
 }
 
-APZSampler::~APZSampler() = default;
+APZSampler::~APZSampler()
+{
+  mApz->SetSampler(nullptr);
+}
 
 void
 APZSampler::ClearTree()