diff --git a/runtime/class_linker.cc b/runtime/class_linker.cc
index 978c99b..5acef70 100644
--- a/runtime/class_linker.cc
+++ b/runtime/class_linker.cc
@@ -1119,14 +1119,15 @@
 // Keep in sync with InitCallback. Anything we visit, we need to
 // reinit references to when reinitializing a ClassLinker from a
 // mapped image.
-void ClassLinker::VisitRoots(RootVisitor* visitor, void* arg, bool only_dirty, bool clean_dirty) {
-  class_roots_ = down_cast<mirror::ObjectArray<mirror::Class>*>(visitor(class_roots_, arg));
+void ClassLinker::VisitRoots(RootCallback* callback, void* arg, bool only_dirty, bool clean_dirty) {
+  class_roots_ = down_cast<mirror::ObjectArray<mirror::Class>*>(
+      callback(class_roots_, arg, 0, kRootVMInternal));
   Thread* self = Thread::Current();
   {
     ReaderMutexLock mu(self, dex_lock_);
     if (!only_dirty || dex_caches_dirty_) {
       for (mirror::DexCache*& dex_cache : dex_caches_) {
-        dex_cache = down_cast<mirror::DexCache*>(visitor(dex_cache, arg));
+        dex_cache = down_cast<mirror::DexCache*>(callback(dex_cache, arg, 0, kRootVMInternal));
         DCHECK(dex_cache != nullptr);
       }
       if (clean_dirty) {
@@ -1139,7 +1140,7 @@
     WriterMutexLock mu(self, *Locks::classlinker_classes_lock_);
     if (!only_dirty || class_table_dirty_) {
       for (std::pair<const size_t, mirror::Class*>& it : class_table_) {
-        it.second = down_cast<mirror::Class*>(visitor(it.second, arg));
+        it.second = down_cast<mirror::Class*>(callback(it.second, arg, 0, kRootStickyClass));
         DCHECK(it.second != nullptr);
       }
       if (clean_dirty) {
@@ -1151,7 +1152,8 @@
     // handle image roots by using the MS/CMS rescanning of dirty cards.
   }
 
-  array_iftable_ = reinterpret_cast<mirror::IfTable*>(visitor(array_iftable_, arg));
+  array_iftable_ = reinterpret_cast<mirror::IfTable*>(callback(array_iftable_, arg, 0,
+                                                               kRootVMInternal));
   DCHECK(array_iftable_ != nullptr);
 }
 
diff --git a/runtime/class_linker.h b/runtime/class_linker.h
index 7e31356..0745ee2 100644
--- a/runtime/class_linker.h
+++ b/runtime/class_linker.h
@@ -26,8 +26,8 @@
 #include "dex_file.h"
 #include "gtest/gtest.h"
 #include "jni.h"
-#include "root_visitor.h"
 #include "oat_file.h"
+#include "object_callbacks.h"
 
 namespace art {
 namespace gc {
@@ -235,7 +235,7 @@
       LOCKS_EXCLUDED(dex_lock_)
       SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
 
-  void VisitRoots(RootVisitor* visitor, void* arg, bool only_dirty, bool clean_dirty)
+  void VisitRoots(RootCallback* callback, void* arg, bool only_dirty, bool clean_dirty)
       LOCKS_EXCLUDED(Locks::classlinker_classes_lock_, dex_lock_);
 
   mirror::DexCache* FindDexCache(const DexFile& dex_file) const
diff --git a/runtime/class_linker_test.cc b/runtime/class_linker_test.cc
index fb979c2..d9ef0c1 100644
--- a/runtime/class_linker_test.cc
+++ b/runtime/class_linker_test.cc
@@ -339,7 +339,7 @@
     }
   }
 
-  static mirror::Object* TestRootVisitor(mirror::Object* root, void*) {
+  static mirror::Object* TestRootVisitor(mirror::Object* root, void*, uint32_t, RootType) {
     EXPECT_TRUE(root != NULL);
     return root;
   }
diff --git a/runtime/debugger.cc b/runtime/debugger.cc
index 8280c7c..67db2ab 100644
--- a/runtime/debugger.cc
+++ b/runtime/debugger.cc
@@ -85,17 +85,17 @@
     return depth;
   }
 
-  void UpdateObjectPointers(RootVisitor* visitor, void* arg)
+  void UpdateObjectPointers(IsMarkedCallback* callback, void* arg)
       SHARED_LOCKS_REQUIRED(Locks::mutator_lock_) {
     if (type != nullptr) {
-      type = down_cast<mirror::Class*>(visitor(type, arg));
+      type = down_cast<mirror::Class*>(callback(type, arg));
     }
     for (size_t stack_frame = 0; stack_frame < kMaxAllocRecordStackDepth; ++stack_frame) {
       mirror::ArtMethod*& m = stack[stack_frame].method;
       if (m == nullptr) {
         break;
       }
-      m = down_cast<mirror::ArtMethod*>(visitor(m, arg));
+      m = down_cast<mirror::ArtMethod*>(callback(m, arg));
     }
   }
 };
@@ -3793,7 +3793,7 @@
   }
 }
 
-void Dbg::UpdateObjectPointers(RootVisitor* visitor, void* arg) {
+void Dbg::UpdateObjectPointers(IsMarkedCallback* visitor, void* arg) {
   {
     MutexLock mu(Thread::Current(), gAllocTrackerLock);
     if (recent_allocation_records_ != nullptr) {
diff --git a/runtime/debugger.h b/runtime/debugger.h
index f1e3f45..5d269ee 100644
--- a/runtime/debugger.h
+++ b/runtime/debugger.h
@@ -29,7 +29,7 @@
 #include "jdwp/jdwp.h"
 #include "jni.h"
 #include "jvalue.h"
-#include "root_visitor.h"
+#include "object_callbacks.h"
 #include "thread_state.h"
 
 namespace art {
@@ -453,7 +453,7 @@
   static void DumpRecentAllocations();
 
   // Updates the stored direct object pointers (called from SweepSystemWeaks).
-  static void UpdateObjectPointers(RootVisitor* visitor, void* arg)
+  static void UpdateObjectPointers(IsMarkedCallback* callback, void* arg)
       SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
 
   enum HpifWhen {
diff --git a/runtime/gc/accounting/heap_bitmap.cc b/runtime/gc/accounting/heap_bitmap.cc
index c520ee6..f94cf24 100644
--- a/runtime/gc/accounting/heap_bitmap.cc
+++ b/runtime/gc/accounting/heap_bitmap.cc
@@ -72,12 +72,10 @@
   discontinuous_space_sets_.erase(it);
 }
 
-void HeapBitmap::Walk(SpaceBitmap::Callback* callback, void* arg) {
+void HeapBitmap::Walk(ObjectCallback* callback, void* arg) {
   for (const auto& bitmap : continuous_space_bitmaps_) {
     bitmap->Walk(callback, arg);
   }
-
-  DCHECK(!discontinuous_space_sets_.empty());
   for (const auto& space_set : discontinuous_space_sets_) {
     space_set->Walk(callback, arg);
   }
diff --git a/runtime/gc/accounting/heap_bitmap.h b/runtime/gc/accounting/heap_bitmap.h
index bcf36a2..dde1425 100644
--- a/runtime/gc/accounting/heap_bitmap.h
+++ b/runtime/gc/accounting/heap_bitmap.h
@@ -20,6 +20,7 @@
 #include "base/logging.h"
 #include "gc_allocator.h"
 #include "locks.h"
+#include "object_callbacks.h"
 #include "space_bitmap.h"
 
 namespace art {
@@ -83,7 +84,7 @@
     return NULL;
   }
 
-  void Walk(SpaceBitmap::Callback* callback, void* arg)
+  void Walk(ObjectCallback* callback, void* arg)
       SHARED_LOCKS_REQUIRED(Locks::heap_bitmap_lock_);
 
   template <typename Visitor>
diff --git a/runtime/gc/accounting/mod_union_table.cc b/runtime/gc/accounting/mod_union_table.cc
index 0225f29..aad214a 100644
--- a/runtime/gc/accounting/mod_union_table.cc
+++ b/runtime/gc/accounting/mod_union_table.cc
@@ -70,8 +70,8 @@
 
 class ModUnionUpdateObjectReferencesVisitor {
  public:
-  ModUnionUpdateObjectReferencesVisitor(RootVisitor visitor, void* arg)
-    : visitor_(visitor),
+  ModUnionUpdateObjectReferencesVisitor(RootCallback* callback, void* arg)
+    : callback_(callback),
       arg_(arg) {
   }
 
@@ -80,7 +80,7 @@
                   bool /* is_static */) const SHARED_LOCKS_REQUIRED(Locks::mutator_lock_) {
     // Only add the reference if it is non null and fits our criteria.
     if (ref != nullptr) {
-      Object* new_ref = visitor_(ref, arg_);
+      Object* new_ref = callback_(ref, arg_, 0, kRootVMInternal);
       if (new_ref != ref) {
         // Use SetFieldObjectWithoutWriteBarrier to avoid card mark as an optimization which
         // reduces dirtied pages and improves performance.
@@ -90,26 +90,26 @@
   }
 
  private:
-  RootVisitor* visitor_;
+  RootCallback* const callback_;
   void* arg_;
 };
 
 class ModUnionScanImageRootVisitor {
  public:
-  ModUnionScanImageRootVisitor(RootVisitor visitor, void* arg)
-      : visitor_(visitor), arg_(arg) {}
+  ModUnionScanImageRootVisitor(RootCallback* callback, void* arg)
+      : callback_(callback), arg_(arg) {}
 
   void operator()(Object* root) const
       EXCLUSIVE_LOCKS_REQUIRED(Locks::heap_bitmap_lock_)
       SHARED_LOCKS_REQUIRED(Locks::mutator_lock_) {
     DCHECK(root != NULL);
-    ModUnionUpdateObjectReferencesVisitor ref_visitor(visitor_, arg_);
+    ModUnionUpdateObjectReferencesVisitor ref_visitor(callback_, arg_);
     collector::MarkSweep::VisitObjectReferences(root, ref_visitor, true);
   }
 
  private:
-  RootVisitor* visitor_;
-  void* arg_;
+  RootCallback* const callback_;
+  void* const arg_;
 };
 
 void ModUnionTableReferenceCache::ClearCards() {
@@ -261,7 +261,7 @@
   }
 }
 
-void ModUnionTableReferenceCache::UpdateAndMarkReferences(RootVisitor visitor, void* arg) {
+void ModUnionTableReferenceCache::UpdateAndMarkReferences(RootCallback* callback, void* arg) {
   Heap* heap = GetHeap();
   CardTable* card_table = heap->GetCardTable();
 
@@ -296,7 +296,7 @@
     for (mirror::HeapReference<Object>* obj_ptr : ref.second) {
       Object* obj = obj_ptr->AsMirrorPtr();
       if (obj != nullptr) {
-        Object* new_obj = visitor(obj, arg);
+        Object* new_obj = callback(obj, arg, 0, kRootVMInternal);
         // Avoid dirtying pages in the image unless necessary.
         if (new_obj != obj) {
           obj_ptr->Assign(new_obj);
@@ -318,9 +318,9 @@
 }
 
 // Mark all references to the alloc space(s).
-void ModUnionTableCardCache::UpdateAndMarkReferences(RootVisitor visitor, void* arg) {
+void ModUnionTableCardCache::UpdateAndMarkReferences(RootCallback* callback, void* arg) {
   CardTable* card_table = heap_->GetCardTable();
-  ModUnionScanImageRootVisitor scan_visitor(visitor, arg);
+  ModUnionScanImageRootVisitor scan_visitor(callback, arg);
   SpaceBitmap* bitmap = space_->GetLiveBitmap();
   for (const byte* card_addr : cleared_cards_) {
     uintptr_t start = reinterpret_cast<uintptr_t>(card_table->AddrFromCard(card_addr));
diff --git a/runtime/gc/accounting/mod_union_table.h b/runtime/gc/accounting/mod_union_table.h
index a89dbd1..7d5d8d2 100644
--- a/runtime/gc/accounting/mod_union_table.h
+++ b/runtime/gc/accounting/mod_union_table.h
@@ -19,7 +19,7 @@
 
 #include "gc_allocator.h"
 #include "globals.h"
-#include "root_visitor.h"
+#include "object_callbacks.h"
 #include "safe_map.h"
 
 #include <set>
@@ -69,7 +69,7 @@
   // Update the mod-union table using data stored by ClearCards. There may be multiple ClearCards
   // before a call to update, for example, back-to-back sticky GCs. Also mark references to other
   // spaces which are stored in the mod-union table.
-  virtual void UpdateAndMarkReferences(RootVisitor visitor, void* arg) = 0;
+  virtual void UpdateAndMarkReferences(RootCallback* callback, void* arg) = 0;
 
   // Verification, sanity checks that we don't have clean cards which conflict with out cached data
   // for said cards. Exclusive lock is required since verify sometimes uses
@@ -106,7 +106,7 @@
   void ClearCards();
 
   // Update table based on cleared cards and mark all references to the other spaces.
-  void UpdateAndMarkReferences(RootVisitor visitor, void* arg)
+  void UpdateAndMarkReferences(RootCallback* callback, void* arg)
       SHARED_LOCKS_REQUIRED(Locks::mutator_lock_)
       EXCLUSIVE_LOCKS_REQUIRED(Locks::heap_bitmap_lock_);
 
@@ -142,7 +142,7 @@
   void ClearCards();
 
   // Mark all references to the alloc space(s).
-  void UpdateAndMarkReferences(RootVisitor visitor, void* arg)
+  void UpdateAndMarkReferences(RootCallback* callback, void* arg)
       EXCLUSIVE_LOCKS_REQUIRED(Locks::heap_bitmap_lock_)
       SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
 
diff --git a/runtime/gc/accounting/space_bitmap.cc b/runtime/gc/accounting/space_bitmap.cc
index a080bee..ad4ff1b 100644
--- a/runtime/gc/accounting/space_bitmap.cc
+++ b/runtime/gc/accounting/space_bitmap.cc
@@ -44,7 +44,7 @@
                       reinterpret_cast<void*>(HeapLimit()));
 }
 
-void ObjectSet::Walk(SpaceBitmap::Callback* callback, void* arg) {
+void ObjectSet::Walk(ObjectCallback* callback, void* arg) {
   for (const mirror::Object* obj : contained_) {
     callback(const_cast<mirror::Object*>(obj), arg);
   }
@@ -102,7 +102,7 @@
 
 // Visits set bits in address order.  The callback is not permitted to
 // change the bitmap bits or max during the traversal.
-void SpaceBitmap::Walk(SpaceBitmap::Callback* callback, void* arg) {
+void SpaceBitmap::Walk(ObjectCallback* callback, void* arg) {
   CHECK(bitmap_begin_ != NULL);
   CHECK(callback != NULL);
 
@@ -174,12 +174,12 @@
   }
 }
 
-static void WalkFieldsInOrder(SpaceBitmap* visited, SpaceBitmap::Callback* callback, mirror::Object* obj,
+static void WalkFieldsInOrder(SpaceBitmap* visited, ObjectCallback* callback, mirror::Object* obj,
                               void* arg);
 
 // Walk instance fields of the given Class. Separate function to allow recursion on the super
 // class.
-static void WalkInstanceFields(SpaceBitmap* visited, SpaceBitmap::Callback* callback, mirror::Object* obj,
+static void WalkInstanceFields(SpaceBitmap* visited, ObjectCallback* callback, mirror::Object* obj,
                                mirror::Class* klass, void* arg)
     SHARED_LOCKS_REQUIRED(Locks::mutator_lock_) {
   // Visit fields of parent classes first.
@@ -204,7 +204,7 @@
 }
 
 // For an unvisited object, visit it then all its children found via fields.
-static void WalkFieldsInOrder(SpaceBitmap* visited, SpaceBitmap::Callback* callback, mirror::Object* obj,
+static void WalkFieldsInOrder(SpaceBitmap* visited, ObjectCallback* callback, mirror::Object* obj,
                               void* arg)
     SHARED_LOCKS_REQUIRED(Locks::mutator_lock_) {
   if (visited->Test(obj)) {
@@ -246,7 +246,7 @@
 
 // Visits set bits with an in order traversal.  The callback is not permitted to change the bitmap
 // bits or max during the traversal.
-void SpaceBitmap::InOrderWalk(SpaceBitmap::Callback* callback, void* arg) {
+void SpaceBitmap::InOrderWalk(ObjectCallback* callback, void* arg) {
   UniquePtr<SpaceBitmap> visited(Create("bitmap for in-order walk",
                                        reinterpret_cast<byte*>(heap_begin_),
                                        IndexToOffset(bitmap_size_ / kWordSize)));
diff --git a/runtime/gc/accounting/space_bitmap.h b/runtime/gc/accounting/space_bitmap.h
index aa074eb..3c4b674 100644
--- a/runtime/gc/accounting/space_bitmap.h
+++ b/runtime/gc/accounting/space_bitmap.h
@@ -17,10 +17,11 @@
 #ifndef ART_RUNTIME_GC_ACCOUNTING_SPACE_BITMAP_H_
 #define ART_RUNTIME_GC_ACCOUNTING_SPACE_BITMAP_H_
 
-#include "locks.h"
 #include "gc_allocator.h"
 #include "globals.h"
+#include "locks.h"
 #include "mem_map.h"
+#include "object_callbacks.h"
 #include "UniquePtr.h"
 
 #include <limits.h>
@@ -42,8 +43,6 @@
   // Alignment of objects within spaces.
   static const size_t kAlignment = 8;
 
-  typedef void Callback(mirror::Object* obj, void* arg);
-
   typedef void ScanCallback(mirror::Object* obj, void* finger, void* arg);
 
   typedef void SweepCallback(size_t ptr_count, mirror::Object** ptrs, void* arg);
@@ -102,7 +101,7 @@
     return index < bitmap_size_ / kWordSize;
   }
 
-  void VisitRange(uintptr_t base, uintptr_t max, Callback* visitor, void* arg) const;
+  void VisitRange(uintptr_t base, uintptr_t max, ObjectCallback* callback, void* arg) const;
 
   class ClearVisitor {
    public:
@@ -129,10 +128,10 @@
       EXCLUSIVE_LOCKS_REQUIRED(Locks::heap_bitmap_lock_)
       SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
 
-  void Walk(Callback* callback, void* arg)
+  void Walk(ObjectCallback* callback, void* arg)
       SHARED_LOCKS_REQUIRED(Locks::heap_bitmap_lock_);
 
-  void InOrderWalk(Callback* callback, void* arg)
+  void InOrderWalk(ObjectCallback* callback, void* arg)
       SHARED_LOCKS_REQUIRED(Locks::heap_bitmap_lock_, Locks::mutator_lock_);
 
   static void SweepWalk(const SpaceBitmap& live, const SpaceBitmap& mark, uintptr_t base,
@@ -249,7 +248,7 @@
     contained_ = space_set.contained_;
   }
 
-  void Walk(SpaceBitmap::Callback* callback, void* arg)
+  void Walk(ObjectCallback* callback, void* arg)
       SHARED_LOCKS_REQUIRED(GlobalSynchronization::heap_bitmap_lock_);
 
   template <typename Visitor>
diff --git a/runtime/gc/collector/mark_sweep.cc b/runtime/gc/collector/mark_sweep.cc
index 862d06f..de9f59e 100644
--- a/runtime/gc/collector/mark_sweep.cc
+++ b/runtime/gc/collector/mark_sweep.cc
@@ -525,14 +525,16 @@
   }
 }
 
-Object* MarkSweep::MarkRootParallelCallback(Object* root, void* arg) {
+mirror::Object* MarkSweep::MarkRootParallelCallback(mirror::Object* root, void* arg,
+                                                    uint32_t /*thread_id*/, RootType /*root_type*/) {
   DCHECK(root != NULL);
   DCHECK(arg != NULL);
   reinterpret_cast<MarkSweep*>(arg)->MarkObjectNonNullParallel(root);
   return root;
 }
 
-Object* MarkSweep::MarkRootCallback(Object* root, void* arg) {
+Object* MarkSweep::MarkRootCallback(Object* root, void* arg, uint32_t /*thread_id*/,
+                                    RootType /*root_type*/) {
   DCHECK(root != nullptr);
   DCHECK(arg != nullptr);
   reinterpret_cast<MarkSweep*>(arg)->MarkObjectNonNull(root);
@@ -930,7 +932,7 @@
   ProcessMarkStack(false);
 }
 
-mirror::Object* MarkSweep::IsMarkedCallback(Object* object, void* arg) {
+mirror::Object* MarkSweep::IsMarkedCallback(mirror::Object* object, void* arg) {
   if (reinterpret_cast<MarkSweep*>(arg)->IsMarked(object)) {
     return object;
   }
diff --git a/runtime/gc/collector/mark_sweep.h b/runtime/gc/collector/mark_sweep.h
index bfedac7..8bc0bb5 100644
--- a/runtime/gc/collector/mark_sweep.h
+++ b/runtime/gc/collector/mark_sweep.h
@@ -22,8 +22,8 @@
 #include "base/macros.h"
 #include "base/mutex.h"
 #include "garbage_collector.h"
+#include "object_callbacks.h"
 #include "offsets.h"
-#include "root_visitor.h"
 #include "UniquePtr.h"
 
 namespace art {
@@ -180,11 +180,13 @@
       SHARED_LOCKS_REQUIRED(Locks::mutator_lock_)
       EXCLUSIVE_LOCKS_REQUIRED(Locks::heap_bitmap_lock_);
 
-  static mirror::Object* MarkRootCallback(mirror::Object* root, void* arg)
+  static mirror::Object* MarkRootCallback(mirror::Object* root, void* arg, uint32_t thread_id,
+                                          RootType root_type)
       SHARED_LOCKS_REQUIRED(Locks::mutator_lock_)
       EXCLUSIVE_LOCKS_REQUIRED(Locks::heap_bitmap_lock_);
 
-  static mirror::Object* MarkRootParallelCallback(mirror::Object* root, void* arg);
+  static mirror::Object* MarkRootParallelCallback(mirror::Object* root, void* arg,
+                                                  uint32_t thread_id, RootType root_type);
 
   // Marks an object.
   void MarkObject(const mirror::Object* obj)
diff --git a/runtime/gc/collector/semi_space.cc b/runtime/gc/collector/semi_space.cc
index 0c6a938..b37b9d2 100644
--- a/runtime/gc/collector/semi_space.cc
+++ b/runtime/gc/collector/semi_space.cc
@@ -513,7 +513,7 @@
   return forward_address;
 }
 
-Object* SemiSpace::RecursiveMarkObjectCallback(Object* root, void* arg) {
+mirror::Object* SemiSpace::RecursiveMarkObjectCallback(mirror::Object* root, void* arg) {
   DCHECK(root != nullptr);
   DCHECK(arg != nullptr);
   SemiSpace* semi_space = reinterpret_cast<SemiSpace*>(arg);
@@ -522,7 +522,8 @@
   return ret;
 }
 
-Object* SemiSpace::MarkRootCallback(Object* root, void* arg) {
+Object* SemiSpace::MarkRootCallback(Object* root, void* arg, uint32_t /*thread_id*/,
+                                    RootType /*root_type*/) {
   DCHECK(root != nullptr);
   DCHECK(arg != nullptr);
   return reinterpret_cast<SemiSpace*>(arg)->MarkObject(root);
@@ -536,7 +537,7 @@
   timings_.EndSplit();
 }
 
-mirror::Object* SemiSpace::MarkedForwardingAddressCallback(Object* object, void* arg) {
+mirror::Object* SemiSpace::MarkedForwardingAddressCallback(mirror::Object* object, void* arg) {
   return reinterpret_cast<SemiSpace*>(arg)->GetMarkedForwardAddress(object);
 }
 
diff --git a/runtime/gc/collector/semi_space.h b/runtime/gc/collector/semi_space.h
index 685b33c..f58402f 100644
--- a/runtime/gc/collector/semi_space.h
+++ b/runtime/gc/collector/semi_space.h
@@ -22,8 +22,8 @@
 #include "base/macros.h"
 #include "base/mutex.h"
 #include "garbage_collector.h"
+#include "object_callbacks.h"
 #include "offsets.h"
-#include "root_visitor.h"
 #include "UniquePtr.h"
 
 namespace art {
@@ -142,7 +142,8 @@
   static void VisitObjectReferencesAndClass(mirror::Object* obj, const Visitor& visitor)
       EXCLUSIVE_LOCKS_REQUIRED(Locks::heap_bitmap_lock_, Locks::mutator_lock_);
 
-  static mirror::Object* MarkRootCallback(mirror::Object* root, void* arg)
+  static mirror::Object* MarkRootCallback(mirror::Object* root, void* arg, uint32_t /*tid*/,
+                                          RootType /*root_type*/)
       EXCLUSIVE_LOCKS_REQUIRED(Locks::heap_bitmap_lock_, Locks::mutator_lock_);
 
   static mirror::Object* RecursiveMarkObjectCallback(mirror::Object* root, void* arg)
diff --git a/runtime/gc/heap.cc b/runtime/gc/heap.cc
index 62567d7..9c828b2 100644
--- a/runtime/gc/heap.cc
+++ b/runtime/gc/heap.cc
@@ -369,7 +369,7 @@
   }
 }
 
-void Heap::VisitObjects(ObjectVisitorCallback callback, void* arg) {
+void Heap::VisitObjects(ObjectCallback callback, void* arg) {
   Thread* self = Thread::Current();
   // GCs can move objects, so don't allow this.
   const char* old_cause = self->StartAssertNoThreadSuspension("Visiting objects");
@@ -604,8 +604,8 @@
 }
 
 struct SoftReferenceArgs {
-  RootVisitor* is_marked_callback_;
-  RootVisitor* recursive_mark_callback_;
+  IsMarkedCallback* is_marked_callback_;
+  MarkObjectCallback* recursive_mark_callback_;
   void* arg_;
 };
 
@@ -617,8 +617,8 @@
 
 // Process reference class instances and schedule finalizations.
 void Heap::ProcessReferences(TimingLogger& timings, bool clear_soft,
-                             RootVisitor* is_marked_callback,
-                             RootVisitor* recursive_mark_object_callback, void* arg) {
+                             IsMarkedCallback* is_marked_callback,
+                             MarkObjectCallback* recursive_mark_object_callback, void* arg) {
   // Unless we are in the zygote or required to clear soft references with white references,
   // preserve some white referents.
   if (!clear_soft && !Runtime::Current()->IsZygote()) {
@@ -671,13 +671,13 @@
 // Process the "referent" field in a java.lang.ref.Reference.  If the referent has not yet been
 // marked, put it on the appropriate list in the heap for later processing.
 void Heap::DelayReferenceReferent(mirror::Class* klass, mirror::Object* obj,
-                                  RootVisitor mark_visitor, void* arg) {
+                                  IsMarkedCallback is_marked_callback, void* arg) {
   DCHECK(klass != nullptr);
   DCHECK(klass->IsReferenceClass());
   DCHECK(obj != nullptr);
   mirror::Object* referent = GetReferenceReferent(obj);
   if (referent != nullptr) {
-    mirror::Object* forward_address = mark_visitor(referent, arg);
+    mirror::Object* forward_address = is_marked_callback(referent, arg);
     // Null means that the object is not currently marked.
     if (forward_address == nullptr) {
       Thread* self = Thread::Current();
@@ -1169,7 +1169,7 @@
 
 void Heap::GetReferringObjects(mirror::Object* o, int32_t max_count,
                                std::vector<mirror::Object*>& referring_objects) {
-  // Can't do any GC in this function since this may move classes.
+  // Can't do any GC in this function since this may move the object o.
   Thread* self = Thread::Current();
   auto* old_cause = self->StartAssertNoThreadSuspension("GetReferringObjects");
   ReferringObjectsFinder finder(o, max_count, referring_objects);
@@ -1696,7 +1696,8 @@
   gc_complete_cond_->Broadcast(self);
 }
 
-static mirror::Object* RootMatchesObjectVisitor(mirror::Object* root, void* arg) {
+static mirror::Object* RootMatchesObjectVisitor(mirror::Object* root, void* arg,
+                                                uint32_t /*thread_id*/, RootType /*root_type*/) {
   mirror::Object* obj = reinterpret_cast<mirror::Object*>(arg);
   if (root == obj) {
     LOG(INFO) << "Object " << obj << " is a root";
@@ -1823,7 +1824,8 @@
     return heap_->IsLiveObjectLocked(obj, true, false, true);
   }
 
-  static mirror::Object* VerifyRoots(mirror::Object* root, void* arg) {
+  static mirror::Object* VerifyRoots(mirror::Object* root, void* arg, uint32_t /*thread_id*/,
+                                     RootType /*root_type*/) {
     VerifyReferenceVisitor* visitor = reinterpret_cast<VerifyReferenceVisitor*>(arg);
     (*visitor)(nullptr, root, MemberOffset(0), true);
     return root;
@@ -2041,7 +2043,7 @@
   }
 }
 
-static mirror::Object* IdentityCallback(mirror::Object* obj, void*) {
+static mirror::Object* IdentityRootCallback(mirror::Object* obj, void*, uint32_t, RootType) {
   return obj;
 }
 
@@ -2080,7 +2082,7 @@
     ReaderMutexLock reader_lock(self, *Locks::heap_bitmap_lock_);
     for (const auto& table_pair : mod_union_tables_) {
       accounting::ModUnionTable* mod_union_table = table_pair.second;
-      mod_union_table->UpdateAndMarkReferences(IdentityCallback, nullptr);
+      mod_union_table->UpdateAndMarkReferences(IdentityRootCallback, nullptr);
       mod_union_table->Verify();
     }
     thread_list->ResumeAll();
diff --git a/runtime/gc/heap.h b/runtime/gc/heap.h
index 476ceee..368a687 100644
--- a/runtime/gc/heap.h
+++ b/runtime/gc/heap.h
@@ -32,9 +32,9 @@
 #include "gtest/gtest.h"
 #include "jni.h"
 #include "locks.h"
+#include "object_callbacks.h"
 #include "offsets.h"
 #include "reference_queue.h"
-#include "root_visitor.h"
 #include "safe_map.h"
 #include "thread_pool.h"
 
@@ -183,7 +183,7 @@
   }
 
   // Visit all of the live objects in the heap.
-  void VisitObjects(ObjectVisitorCallback callback, void* arg)
+  void VisitObjects(ObjectCallback callback, void* arg)
       SHARED_LOCKS_REQUIRED(Locks::heap_bitmap_lock_, Locks::mutator_lock_);
 
   void SwapSemiSpaces() EXCLUSIVE_LOCKS_REQUIRED(Locks::mutator_lock_);
@@ -328,8 +328,9 @@
     return finalizer_reference_zombie_offset_;
   }
   static mirror::Object* PreserveSoftReferenceCallback(mirror::Object* obj, void* arg);
-  void ProcessReferences(TimingLogger& timings, bool clear_soft, RootVisitor* is_marked_callback,
-                         RootVisitor* recursive_mark_object_callback, void* arg)
+  void ProcessReferences(TimingLogger& timings, bool clear_soft,
+                         IsMarkedCallback* is_marked_callback,
+                         MarkObjectCallback* recursive_mark_object_callback, void* arg)
       SHARED_LOCKS_REQUIRED(Locks::mutator_lock_)
       EXCLUSIVE_LOCKS_REQUIRED(Locks::heap_bitmap_lock_);
 
@@ -605,8 +606,9 @@
   // Returns true if the reference object has not yet been enqueued.
   bool IsEnqueuable(mirror::Object* ref) const SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
   bool IsEnqueued(mirror::Object* ref) const SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
-  void DelayReferenceReferent(mirror::Class* klass, mirror::Object* obj, RootVisitor mark_visitor,
-                              void* arg) SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
+  void DelayReferenceReferent(mirror::Class* klass, mirror::Object* obj,
+                              IsMarkedCallback is_marked_callback, void* arg)
+      SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
 
   // Run the finalizers.
   void RunFinalization(JNIEnv* env);
diff --git a/runtime/gc/reference_queue.cc b/runtime/gc/reference_queue.cc
index 2d73a71..fae4cac 100644
--- a/runtime/gc/reference_queue.cc
+++ b/runtime/gc/reference_queue.cc
@@ -94,13 +94,14 @@
   }
 }
 
-void ReferenceQueue::ClearWhiteReferences(ReferenceQueue& cleared_references, RootVisitor visitor,
+void ReferenceQueue::ClearWhiteReferences(ReferenceQueue& cleared_references,
+                                          IsMarkedCallback* preserve_callback,
                                           void* arg) {
   while (!IsEmpty()) {
     mirror::Object* ref = DequeuePendingReference();
     mirror::Object* referent = heap_->GetReferenceReferent(ref);
     if (referent != nullptr) {
-      mirror::Object* forward_address = visitor(referent, arg);
+      mirror::Object* forward_address = preserve_callback(referent, arg);
       if (forward_address == nullptr) {
         // Referent is white, clear it.
         heap_->ClearReferenceReferent(ref);
@@ -108,7 +109,7 @@
           cleared_references.EnqueuePendingReference(ref);
         }
       } else if (referent != forward_address) {
-        // Object moved, need to updated the referrent.
+        // Object moved, need to updated the referent.
         heap_->SetReferenceReferent(ref, forward_address);
       }
     }
@@ -116,8 +117,9 @@
 }
 
 void ReferenceQueue::EnqueueFinalizerReferences(ReferenceQueue& cleared_references,
-                                                RootVisitor is_marked_callback,
-                                                RootVisitor recursive_mark_callback, void* arg) {
+                                                IsMarkedCallback is_marked_callback,
+                                                MarkObjectCallback recursive_mark_callback,
+                                                void* arg) {
   while (!IsEmpty()) {
     mirror::Object* ref = DequeuePendingReference();
     mirror::Object* referent = heap_->GetReferenceReferent(ref);
@@ -139,7 +141,7 @@
   }
 }
 
-void ReferenceQueue::PreserveSomeSoftReferences(RootVisitor preserve_callback, void* arg) {
+void ReferenceQueue::PreserveSomeSoftReferences(IsMarkedCallback preserve_callback, void* arg) {
   ReferenceQueue cleared(heap_);
   while (!IsEmpty()) {
     mirror::Object* ref = DequeuePendingReference();
@@ -149,7 +151,7 @@
       if (forward_address == nullptr) {
         // Either the reference isn't marked or we don't wish to preserve it.
         cleared.EnqueuePendingReference(ref);
-      } else {
+      } else if (forward_address != referent) {
         heap_->SetReferenceReferent(ref, forward_address);
       }
     }
diff --git a/runtime/gc/reference_queue.h b/runtime/gc/reference_queue.h
index 3f3069e..e12a95f 100644
--- a/runtime/gc/reference_queue.h
+++ b/runtime/gc/reference_queue.h
@@ -27,8 +27,8 @@
 #include "gtest/gtest.h"
 #include "jni.h"
 #include "locks.h"
+#include "object_callbacks.h"
 #include "offsets.h"
-#include "root_visitor.h"
 #include "thread_pool.h"
 
 namespace art {
@@ -56,17 +56,18 @@
   // Enqueues finalizer references with white referents.  White referents are blackened, moved to the
   // zombie field, and the referent field is cleared.
   void EnqueueFinalizerReferences(ReferenceQueue& cleared_references,
-                                  RootVisitor is_marked_callback,
-                                  RootVisitor recursive_mark_callback, void* arg)
+                                  IsMarkedCallback is_marked_callback,
+                                  MarkObjectCallback recursive_mark_callback, void* arg)
       SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
   // Walks the reference list marking any references subject to the reference clearing policy.
   // References with a black referent are removed from the list.  References with white referents
   // biased toward saving are blackened and also removed from the list.
-  void PreserveSomeSoftReferences(RootVisitor preserve_callback, void* arg)
+  void PreserveSomeSoftReferences(IsMarkedCallback* preserve_callback, void* arg)
       SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
   // Unlink the reference list clearing references objects with white referents.  Cleared references
   // registered to a reference queue are scheduled for appending by the heap worker thread.
-  void ClearWhiteReferences(ReferenceQueue& cleared_references, RootVisitor visitor, void* arg)
+  void ClearWhiteReferences(ReferenceQueue& cleared_references, IsMarkedCallback is_marked_callback,
+                            void* arg)
       SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
   void Dump(std::ostream& os) const
         SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
diff --git a/runtime/gc/space/bump_pointer_space.cc b/runtime/gc/space/bump_pointer_space.cc
index a314d74..2e07bd3 100644
--- a/runtime/gc/space/bump_pointer_space.cc
+++ b/runtime/gc/space/bump_pointer_space.cc
@@ -137,7 +137,7 @@
   return storage;
 }
 
-void BumpPointerSpace::Walk(ObjectVisitorCallback callback, void* arg) {
+void BumpPointerSpace::Walk(ObjectCallback* callback, void* arg) {
   byte* pos = Begin();
 
   {
diff --git a/runtime/gc/space/bump_pointer_space.h b/runtime/gc/space/bump_pointer_space.h
index d73fe3b..ddd17be 100644
--- a/runtime/gc/space/bump_pointer_space.h
+++ b/runtime/gc/space/bump_pointer_space.h
@@ -17,7 +17,7 @@
 #ifndef ART_RUNTIME_GC_SPACE_BUMP_POINTER_SPACE_H_
 #define ART_RUNTIME_GC_SPACE_BUMP_POINTER_SPACE_H_
 
-#include "root_visitor.h"
+#include "object_callbacks.h"
 #include "space.h"
 
 namespace art {
@@ -121,7 +121,7 @@
   }
 
   // Go through all of the blocks and visit the continuous objects.
-  void Walk(ObjectVisitorCallback callback, void* arg)
+  void Walk(ObjectCallback* callback, void* arg)
       SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
 
   // Object alignment within the space.
diff --git a/runtime/hprof/hprof.cc b/runtime/hprof/hprof.cc
index 24d403d..ae03dd9 100644
--- a/runtime/hprof/hprof.cc
+++ b/runtime/hprof/hprof.cc
@@ -431,12 +431,8 @@
     Runtime::Current()->VisitRoots(RootVisitor, this, false, false);
     Thread* self = Thread::Current();
     {
-      WriterMutexLock mu(self, *Locks::heap_bitmap_lock_);
-      Runtime::Current()->GetHeap()->FlushAllocStack();
-    }
-    {
       ReaderMutexLock mu(self, *Locks::heap_bitmap_lock_);
-      Runtime::Current()->GetHeap()->GetLiveBitmap()->Walk(HeapBitmapCallback, this);
+      Runtime::Current()->GetHeap()->VisitObjects(VisitObjectCallback, this);
     }
     current_record_.StartNewRecord(body_fp_, HPROF_TAG_HEAP_DUMP_END, HPROF_TIME);
     current_record_.Flush();
@@ -500,22 +496,23 @@
   }
 
  private:
-  static mirror::Object* RootVisitor(mirror::Object* obj, void* arg)
+  static mirror::Object* RootVisitor(mirror::Object* obj, void* arg, uint32_t thread_id,
+                                     RootType root_type)
       SHARED_LOCKS_REQUIRED(Locks::mutator_lock_) {
     DCHECK(arg != NULL);
-    reinterpret_cast<Hprof*>(arg)->VisitRoot(obj);
+    reinterpret_cast<Hprof*>(arg)->VisitRoot(obj, thread_id, root_type);
     return obj;
   }
 
-  static void HeapBitmapCallback(mirror::Object* obj, void* arg)
+  static void VisitObjectCallback(mirror::Object* obj, void* arg)
       SHARED_LOCKS_REQUIRED(Locks::mutator_lock_) {
-    CHECK(obj != NULL);
-    CHECK(arg != NULL);
-    Hprof* hprof = reinterpret_cast<Hprof*>(arg);
-    hprof->DumpHeapObject(obj);
+    DCHECK(obj != NULL);
+    DCHECK(arg != NULL);
+    reinterpret_cast<Hprof*>(arg)->DumpHeapObject(obj);
   }
 
-  void VisitRoot(const mirror::Object* obj) SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
+  void VisitRoot(const mirror::Object* obj, uint32_t thread_id, RootType type)
+      SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
 
   int DumpHeapObject(mirror::Object* obj) SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
 
@@ -1050,10 +1047,7 @@
   return 0;
 }
 
-void Hprof::VisitRoot(const mirror::Object* obj) {
-  uint32_t threadId = 0;  // TODO
-  /*RootType*/ size_t type = 0;  // TODO
-
+void Hprof::VisitRoot(const mirror::Object* obj, uint32_t thread_id, RootType type) {
   static const HprofHeapTag xlate[] = {
     HPROF_ROOT_UNKNOWN,
     HPROF_ROOT_JNI_GLOBAL,
@@ -1071,13 +1065,12 @@
     HPROF_ROOT_VM_INTERNAL,
     HPROF_ROOT_JNI_MONITOR,
   };
-
   CHECK_LT(type, sizeof(xlate) / sizeof(HprofHeapTag));
   if (obj == NULL) {
     return;
   }
   gc_scan_state_ = xlate[type];
-  gc_thread_serial_number_ = threadId;
+  gc_thread_serial_number_ = thread_id;
   MarkRootObject(obj, 0);
   gc_scan_state_ = 0;
   gc_thread_serial_number_ = 0;
diff --git a/runtime/indirect_reference_table.cc b/runtime/indirect_reference_table.cc
index 8194a0d..4a02d74 100644
--- a/runtime/indirect_reference_table.cc
+++ b/runtime/indirect_reference_table.cc
@@ -309,9 +309,10 @@
   return true;
 }
 
-void IndirectReferenceTable::VisitRoots(RootVisitor* visitor, void* arg) {
+void IndirectReferenceTable::VisitRoots(RootCallback* callback, void* arg, uint32_t tid,
+                                        RootType root_type) {
   for (auto ref : *this) {
-    *ref = visitor(const_cast<mirror::Object*>(*ref), arg);
+    *ref = callback(const_cast<mirror::Object*>(*ref), arg, tid, root_type);
     DCHECK(*ref != nullptr);
   }
 }
diff --git a/runtime/indirect_reference_table.h b/runtime/indirect_reference_table.h
index 21e942e..9d2fa35 100644
--- a/runtime/indirect_reference_table.h
+++ b/runtime/indirect_reference_table.h
@@ -23,8 +23,8 @@
 #include <string>
 
 #include "base/logging.h"
+#include "object_callbacks.h"
 #include "offsets.h"
-#include "root_visitor.h"
 
 namespace art {
 namespace mirror {
@@ -307,7 +307,7 @@
     return IrtIterator(table_, Capacity(), Capacity());
   }
 
-  void VisitRoots(RootVisitor* visitor, void* arg);
+  void VisitRoots(RootCallback* callback, void* arg, uint32_t tid, RootType root_type);
 
   uint32_t GetSegmentState() const {
     return segment_state_.all;
diff --git a/runtime/intern_table.cc b/runtime/intern_table.cc
index a829e97..5693747 100644
--- a/runtime/intern_table.cc
+++ b/runtime/intern_table.cc
@@ -43,15 +43,16 @@
      << weak_interns_.size() << " weak\n";
 }
 
-void InternTable::VisitRoots(RootVisitor* visitor, void* arg,
+void InternTable::VisitRoots(RootCallback* callback, void* arg,
                              bool only_dirty, bool clean_dirty) {
   MutexLock mu(Thread::Current(), intern_table_lock_);
   if (!only_dirty || is_dirty_) {
     for (auto& strong_intern : strong_interns_) {
-      strong_intern.second = down_cast<mirror::String*>(visitor(strong_intern.second, arg));
+      strong_intern.second =
+          down_cast<mirror::String*>(callback(strong_intern.second, arg, 0,
+                                              kRootInternedString));
       DCHECK(strong_intern.second != nullptr);
     }
-
     if (clean_dirty) {
       is_dirty_ = false;
     }
@@ -196,15 +197,15 @@
 }
 
 mirror::String* InternTable::InternStrong(mirror::String* s) {
-  if (s == NULL) {
-    return NULL;
+  if (s == nullptr) {
+    return nullptr;
   }
   return Insert(s, true);
 }
 
 mirror::String* InternTable::InternWeak(mirror::String* s) {
-  if (s == NULL) {
-    return NULL;
+  if (s == nullptr) {
+    return nullptr;
   }
   return Insert(s, false);
 }
@@ -215,11 +216,11 @@
   return found == s;
 }
 
-void InternTable::SweepInternTableWeaks(RootVisitor visitor, void* arg) {
+void InternTable::SweepInternTableWeaks(IsMarkedCallback* callback, void* arg) {
   MutexLock mu(Thread::Current(), intern_table_lock_);
   for (auto it = weak_interns_.begin(), end = weak_interns_.end(); it != end;) {
     mirror::Object* object = it->second;
-    mirror::Object* new_object = visitor(object, arg);
+    mirror::Object* new_object = callback(object, arg);
     if (new_object == nullptr) {
       // TODO: use it = weak_interns_.erase(it) when we get a c++11 stl.
       weak_interns_.erase(it++);
diff --git a/runtime/intern_table.h b/runtime/intern_table.h
index eec63c8..9f09fb9 100644
--- a/runtime/intern_table.h
+++ b/runtime/intern_table.h
@@ -18,7 +18,7 @@
 #define ART_RUNTIME_INTERN_TABLE_H_
 
 #include "base/mutex.h"
-#include "root_visitor.h"
+#include "object_callbacks.h"
 
 #include <map>
 
@@ -55,13 +55,13 @@
   // Interns a potentially new string in the 'weak' table. (See above.)
   mirror::String* InternWeak(mirror::String* s) SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
 
-  void SweepInternTableWeaks(RootVisitor visitor, void* arg);
+  void SweepInternTableWeaks(IsMarkedCallback* callback, void* arg);
 
   bool ContainsWeak(mirror::String* s) SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
 
   size_t Size() const;
 
-  void VisitRoots(RootVisitor* visitor, void* arg, bool only_dirty, bool clean_dirty);
+  void VisitRoots(RootCallback* callback, void* arg, bool only_dirty, bool clean_dirty);
 
   void DumpForSigQuit(std::ostream& os) const;
 
diff --git a/runtime/intern_table_test.cc b/runtime/intern_table_test.cc
index aa2502d..c328245 100644
--- a/runtime/intern_table_test.cc
+++ b/runtime/intern_table_test.cc
@@ -81,7 +81,7 @@
   mutable std::vector<const mirror::String*> expected_;
 };
 
-mirror::Object* IsMarkedSweepingVisitor(mirror::Object* object, void* arg) {
+mirror::Object* IsMarkedSweepingCallback(mirror::Object* object, void* arg) {
   if (reinterpret_cast<TestPredicate*>(arg)->IsMarked(object)) {
     return object;
   }
@@ -108,7 +108,7 @@
   p.Expect(s1.get());
   {
     ReaderMutexLock mu(soa.Self(), *Locks::heap_bitmap_lock_);
-    t.SweepInternTableWeaks(IsMarkedSweepingVisitor, &p);
+    t.SweepInternTableWeaks(IsMarkedSweepingCallback, &p);
   }
 
   EXPECT_EQ(2U, t.Size());
diff --git a/runtime/jdwp/object_registry.cc b/runtime/jdwp/object_registry.cc
index 40ba3e3..49dceb2 100644
--- a/runtime/jdwp/object_registry.cc
+++ b/runtime/jdwp/object_registry.cc
@@ -206,7 +206,7 @@
   }
 }
 
-void ObjectRegistry::UpdateObjectPointers(RootVisitor visitor, void* arg) {
+void ObjectRegistry::UpdateObjectPointers(IsMarkedCallback* callback, void* arg) {
   MutexLock mu(Thread::Current(), lock_);
   if (object_to_entry_.empty()) {
     return;
@@ -215,7 +215,7 @@
   for (auto& pair : object_to_entry_) {
     mirror::Object* new_obj;
     if (pair.first != nullptr) {
-      new_obj = visitor(pair.first, arg);
+      new_obj = callback(pair.first, arg);
       if (new_obj != nullptr) {
         new_object_to_entry.insert(std::make_pair(new_obj, pair.second));
       }
diff --git a/runtime/jdwp/object_registry.h b/runtime/jdwp/object_registry.h
index 0190575..3c6cb15 100644
--- a/runtime/jdwp/object_registry.h
+++ b/runtime/jdwp/object_registry.h
@@ -26,7 +26,7 @@
 #include "mirror/class.h"
 #include "mirror/class-inl.h"
 #include "mirror/object-inl.h"
-#include "root_visitor.h"
+#include "object_callbacks.h"
 #include "safe_map.h"
 
 namespace art {
@@ -85,7 +85,7 @@
   jobject GetJObject(JDWP::ObjectId id) SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
 
   // Visit, objects are treated as system weaks.
-  void UpdateObjectPointers(RootVisitor visitor, void* arg)
+  void UpdateObjectPointers(IsMarkedCallback* callback, void* arg)
       SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
 
   // We have allow / disallow functionality since we use system weak sweeping logic to update moved
diff --git a/runtime/jni_internal.cc b/runtime/jni_internal.cc
index deea5f6..030b213 100644
--- a/runtime/jni_internal.cc
+++ b/runtime/jni_internal.cc
@@ -523,9 +523,9 @@
     return dlsym(handle_, symbol_name.c_str());
   }
 
-  void VisitRoots(RootVisitor* visitor, void* arg) {
+  void VisitRoots(RootCallback* visitor, void* arg) {
     if (class_loader_ != nullptr) {
-      class_loader_ = visitor(class_loader_, arg);
+      class_loader_ = visitor(class_loader_, arg, 0, kRootVMInternal);
     }
   }
 
@@ -619,9 +619,9 @@
     return NULL;
   }
 
-  void VisitRoots(RootVisitor* visitor, void* arg) {
+  void VisitRoots(RootCallback* callback, void* arg) {
     for (auto& lib_pair : libraries_) {
-      lib_pair.second->VisitRoots(visitor, arg);
+      lib_pair.second->VisitRoots(callback, arg);
     }
   }
 
@@ -3373,11 +3373,11 @@
   return native_method;
 }
 
-void JavaVMExt::SweepJniWeakGlobals(RootVisitor visitor, void* arg) {
+void JavaVMExt::SweepJniWeakGlobals(IsMarkedCallback* callback, void* arg) {
   MutexLock mu(Thread::Current(), weak_globals_lock_);
   for (mirror::Object** entry : weak_globals_) {
     mirror::Object* obj = *entry;
-    mirror::Object* new_obj = visitor(obj, arg);
+    mirror::Object* new_obj = callback(obj, arg);
     if (new_obj == nullptr) {
       new_obj = kClearedJniWeakGlobal;
     }
@@ -3385,20 +3385,20 @@
   }
 }
 
-void JavaVMExt::VisitRoots(RootVisitor* visitor, void* arg) {
+void JavaVMExt::VisitRoots(RootCallback* callback, void* arg) {
   Thread* self = Thread::Current();
   {
     ReaderMutexLock mu(self, globals_lock);
-    globals.VisitRoots(visitor, arg);
+    globals.VisitRoots(callback, arg, 0, kRootJNIGlobal);
   }
   {
     MutexLock mu(self, pins_lock);
-    pin_table.VisitRoots(visitor, arg);
+    pin_table.VisitRoots(callback, arg, 0, kRootVMInternal);
   }
   {
     MutexLock mu(self, libraries_lock);
     // Libraries contains shared libraries which hold a pointer to a class loader.
-    libraries->VisitRoots(visitor, arg);
+    libraries->VisitRoots(callback, arg);
   }
   // The weak_globals table is visited by the GC itself (because it mutates the table).
 }
diff --git a/runtime/jni_internal.h b/runtime/jni_internal.h
index cd3c5cb..26905c7 100644
--- a/runtime/jni_internal.h
+++ b/runtime/jni_internal.h
@@ -22,8 +22,8 @@
 #include "base/macros.h"
 #include "base/mutex.h"
 #include "indirect_reference_table.h"
+#include "object_callbacks.h"
 #include "reference_table.h"
-#include "root_visitor.h"
 #include "runtime.h"
 #include "sirt_ref.h"
 
@@ -91,7 +91,7 @@
 
   void SetCheckJniEnabled(bool enabled);
 
-  void VisitRoots(RootVisitor*, void*);
+  void VisitRoots(RootCallback* callback, void* arg);
 
   void DisallowNewWeakGlobals() EXCLUSIVE_LOCKS_REQUIRED(Locks::mutator_lock_);
   void AllowNewWeakGlobals() SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
@@ -99,7 +99,7 @@
     SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
   void DeleteWeakGlobalRef(Thread* self, jweak obj)
     SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
-  void SweepJniWeakGlobals(RootVisitor visitor, void* arg);
+  void SweepJniWeakGlobals(IsMarkedCallback* callback, void* arg);
   mirror::Object* DecodeWeakGlobal(Thread* self, IndirectRef ref);
 
   Runtime* runtime;
diff --git a/runtime/mirror/array-inl.h b/runtime/mirror/array-inl.h
index b2725e5..35ea2b3 100644
--- a/runtime/mirror/array-inl.h
+++ b/runtime/mirror/array-inl.h
@@ -111,9 +111,9 @@
 }
 
 template<class T>
-inline void PrimitiveArray<T>::VisitRoots(RootVisitor* visitor, void* arg) {
+inline void PrimitiveArray<T>::VisitRoots(RootCallback* callback, void* arg) {
   if (array_class_ != nullptr) {
-    array_class_ = down_cast<Class*>(visitor(array_class_, arg));
+    array_class_ = down_cast<Class*>(callback(array_class_, arg, 0, kRootStickyClass));
   }
 }
 
diff --git a/runtime/mirror/array.h b/runtime/mirror/array.h
index 04f03c3..2e123ef 100644
--- a/runtime/mirror/array.h
+++ b/runtime/mirror/array.h
@@ -18,6 +18,7 @@
 #define ART_RUNTIME_MIRROR_ARRAY_H_
 
 #include "object.h"
+#include "object_callbacks.h"
 #include "gc/heap.h"
 #include "thread.h"
 
@@ -182,7 +183,7 @@
     array_class_ = NULL;
   }
 
-  static void VisitRoots(RootVisitor* visitor, void* arg)
+  static void VisitRoots(RootCallback* callback, void* arg)
       SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
 
  private:
diff --git a/runtime/mirror/art_field.cc b/runtime/mirror/art_field.cc
index c3a4efb..29aade9 100644
--- a/runtime/mirror/art_field.cc
+++ b/runtime/mirror/art_field.cc
@@ -52,10 +52,10 @@
   SetField32(OFFSET_OF_OBJECT_MEMBER(ArtField, offset_), num_bytes.Uint32Value(), false);
 }
 
-void ArtField::VisitRoots(RootVisitor* visitor, void* arg) {
+void ArtField::VisitRoots(RootCallback* callback, void* arg) {
   if (java_lang_reflect_ArtField_ != nullptr) {
     java_lang_reflect_ArtField_ = down_cast<mirror::Class*>(
-        visitor(java_lang_reflect_ArtField_, arg));
+        callback(java_lang_reflect_ArtField_, arg, 0, kRootStickyClass));
   }
 }
 
diff --git a/runtime/mirror/art_field.h b/runtime/mirror/art_field.h
index b33fe4b..716b736 100644
--- a/runtime/mirror/art_field.h
+++ b/runtime/mirror/art_field.h
@@ -20,6 +20,7 @@
 #include "class.h"
 #include "modifiers.h"
 #include "object.h"
+#include "object_callbacks.h"
 
 namespace art {
 
@@ -106,7 +107,7 @@
 
   static void SetClass(Class* java_lang_reflect_ArtField);
   static void ResetClass();
-  static void VisitRoots(RootVisitor* visitor, void* arg)
+  static void VisitRoots(RootCallback* callback, void* arg)
       SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
 
   bool IsVolatile() SHARED_LOCKS_REQUIRED(Locks::mutator_lock_) {
diff --git a/runtime/mirror/art_method.cc b/runtime/mirror/art_method.cc
index 575ea03..3359d59 100644
--- a/runtime/mirror/art_method.cc
+++ b/runtime/mirror/art_method.cc
@@ -40,10 +40,10 @@
 // TODO: get global references for these
 Class* ArtMethod::java_lang_reflect_ArtMethod_ = NULL;
 
-void ArtMethod::VisitRoots(RootVisitor* visitor, void* arg) {
+void ArtMethod::VisitRoots(RootCallback* callback, void* arg) {
   if (java_lang_reflect_ArtMethod_ != nullptr) {
     java_lang_reflect_ArtMethod_ = down_cast<mirror::Class*>(
-        visitor(java_lang_reflect_ArtMethod_, arg));
+        callback(java_lang_reflect_ArtMethod_, arg, 0, kRootStickyClass));
   }
 }
 
diff --git a/runtime/mirror/art_method.h b/runtime/mirror/art_method.h
index bfa7cbe..dfaf063 100644
--- a/runtime/mirror/art_method.h
+++ b/runtime/mirror/art_method.h
@@ -23,7 +23,7 @@
 #include "locks.h"
 #include "modifiers.h"
 #include "object.h"
-#include "root_visitor.h"
+#include "object_callbacks.h"
 
 namespace art {
 
@@ -404,7 +404,7 @@
 
   static void ResetClass();
 
-  static void VisitRoots(RootVisitor* visitor, void* arg)
+  static void VisitRoots(RootCallback* callback, void* arg)
       SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
 
  protected:
diff --git a/runtime/mirror/class.cc b/runtime/mirror/class.cc
index 8051c9b..99a35e3 100644
--- a/runtime/mirror/class.cc
+++ b/runtime/mirror/class.cc
@@ -50,9 +50,10 @@
   java_lang_Class_ = NULL;
 }
 
-void Class::VisitRoots(RootVisitor* visitor, void* arg) {
+void Class::VisitRoots(RootCallback* callback, void* arg) {
   if (java_lang_Class_ != nullptr) {
-    java_lang_Class_ = down_cast<Class*>(visitor(java_lang_Class_, arg));
+    java_lang_Class_ = down_cast<Class*>(
+        callback(java_lang_Class_, arg, 0, kRootStickyClass));
   }
 }
 
diff --git a/runtime/mirror/class.h b/runtime/mirror/class.h
index cbec476..82c8264 100644
--- a/runtime/mirror/class.h
+++ b/runtime/mirror/class.h
@@ -795,7 +795,7 @@
   // Can't call this SetClass or else gets called instead of Object::SetClass in places.
   static void SetClassClass(Class* java_lang_Class);
   static void ResetClass();
-  static void VisitRoots(RootVisitor* visitor, void* arg)
+  static void VisitRoots(RootCallback* callback, void* arg)
       SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
 
   // When class is verified, set the kAccPreverified flag on each method.
diff --git a/runtime/mirror/stack_trace_element.cc b/runtime/mirror/stack_trace_element.cc
index a7ebe07..2e33198 100644
--- a/runtime/mirror/stack_trace_element.cc
+++ b/runtime/mirror/stack_trace_element.cc
@@ -58,9 +58,10 @@
   return trace;
 }
 
-void StackTraceElement::VisitRoots(RootVisitor* visitor, void* arg) {
+void StackTraceElement::VisitRoots(RootCallback* callback, void* arg) {
   if (java_lang_StackTraceElement_ != nullptr) {
-    java_lang_StackTraceElement_ = down_cast<Class*>(visitor(java_lang_StackTraceElement_, arg));
+    java_lang_StackTraceElement_ = down_cast<Class*>(
+        callback(java_lang_StackTraceElement_, arg, 0, kRootStickyClass));
   }
 }
 
diff --git a/runtime/mirror/stack_trace_element.h b/runtime/mirror/stack_trace_element.h
index 73d2673..51817f6 100644
--- a/runtime/mirror/stack_trace_element.h
+++ b/runtime/mirror/stack_trace_element.h
@@ -57,7 +57,7 @@
 
   static void SetClass(Class* java_lang_StackTraceElement);
   static void ResetClass();
-  static void VisitRoots(RootVisitor* visitor, void* arg)
+  static void VisitRoots(RootCallback* callback, void* arg)
       SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
 
  private:
diff --git a/runtime/mirror/string.cc b/runtime/mirror/string.cc
index 10ae066..6f4ead9 100644
--- a/runtime/mirror/string.cc
+++ b/runtime/mirror/string.cc
@@ -280,9 +280,9 @@
   return countDiff;
 }
 
-void String::VisitRoots(RootVisitor* visitor, void* arg) {
+void String::VisitRoots(RootCallback* callback, void* arg) {
   if (java_lang_String_ != nullptr) {
-    java_lang_String_ = down_cast<Class*>(visitor(java_lang_String_, arg));
+    java_lang_String_ = down_cast<Class*>(callback(java_lang_String_, arg, 0, kRootStickyClass));
   }
 }
 
diff --git a/runtime/mirror/string.h b/runtime/mirror/string.h
index 406c5a3..57ec314 100644
--- a/runtime/mirror/string.h
+++ b/runtime/mirror/string.h
@@ -19,7 +19,7 @@
 
 #include "class.h"
 #include "gtest/gtest.h"
-#include "root_visitor.h"
+#include "object_callbacks.h"
 
 namespace art {
 
@@ -107,7 +107,7 @@
 
   static void SetClass(Class* java_lang_String);
   static void ResetClass();
-  static void VisitRoots(RootVisitor* visitor, void* arg)
+  static void VisitRoots(RootCallback* callback, void* arg)
       SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
 
  private:
diff --git a/runtime/mirror/throwable.cc b/runtime/mirror/throwable.cc
index 2318b74..a57bd43 100644
--- a/runtime/mirror/throwable.cc
+++ b/runtime/mirror/throwable.cc
@@ -93,9 +93,10 @@
   java_lang_Throwable_ = NULL;
 }
 
-void Throwable::VisitRoots(RootVisitor* visitor, void* arg) {
+void Throwable::VisitRoots(RootCallback* callback, void* arg) {
   if (java_lang_Throwable_ != nullptr) {
-    java_lang_Throwable_ = down_cast<Class*>(visitor(java_lang_Throwable_, arg));
+    java_lang_Throwable_ = down_cast<Class*>(callback(java_lang_Throwable_, arg, 0,
+                                                      kRootStickyClass));
   }
 }
 
diff --git a/runtime/mirror/throwable.h b/runtime/mirror/throwable.h
index bc9848a..de71957 100644
--- a/runtime/mirror/throwable.h
+++ b/runtime/mirror/throwable.h
@@ -18,7 +18,7 @@
 #define ART_RUNTIME_MIRROR_THROWABLE_H_
 
 #include "object.h"
-#include "root_visitor.h"
+#include "object_callbacks.h"
 #include "string.h"
 
 namespace art {
@@ -51,7 +51,7 @@
 
   static void SetClass(Class* java_lang_Throwable);
   static void ResetClass();
-  static void VisitRoots(RootVisitor* visitor, void* arg)
+  static void VisitRoots(RootCallback* callback, void* arg)
       SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
 
  private:
diff --git a/runtime/monitor.cc b/runtime/monitor.cc
index 72220e0..85f3a09 100644
--- a/runtime/monitor.cc
+++ b/runtime/monitor.cc
@@ -1067,13 +1067,13 @@
   list_.push_front(m);
 }
 
-void MonitorList::SweepMonitorList(RootVisitor visitor, void* arg) {
+void MonitorList::SweepMonitorList(IsMarkedCallback* callback, void* arg) {
   MutexLock mu(Thread::Current(), monitor_list_lock_);
   for (auto it = list_.begin(); it != list_.end(); ) {
     Monitor* m = *it;
     mirror::Object* obj = m->GetObject();
     // The object of a monitor can be null if we have deflated it.
-    mirror::Object* new_obj = obj != nullptr ? visitor(obj, arg) : nullptr;
+    mirror::Object* new_obj = obj != nullptr ? callback(obj, arg) : nullptr;
     if (new_obj == nullptr) {
       VLOG(monitor) << "freeing monitor " << m << " belonging to unmarked object "
                     << m->GetObject();
diff --git a/runtime/monitor.h b/runtime/monitor.h
index 85a8c48..ca95e0b 100644
--- a/runtime/monitor.h
+++ b/runtime/monitor.h
@@ -26,7 +26,7 @@
 
 #include "atomic.h"
 #include "base/mutex.h"
-#include "root_visitor.h"
+#include "object_callbacks.h"
 #include "sirt_ref.h"
 #include "thread_state.h"
 
@@ -220,7 +220,8 @@
 
   void Add(Monitor* m);
 
-  void SweepMonitorList(RootVisitor visitor, void* arg) SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
+  void SweepMonitorList(IsMarkedCallback* callback, void* arg)
+      SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
   void DisallowNewMonitors();
   void AllowNewMonitors();
 
diff --git a/runtime/native/dalvik_system_VMDebug.cc b/runtime/native/dalvik_system_VMDebug.cc
index d9baaaf..6482917 100644
--- a/runtime/native/dalvik_system_VMDebug.cc
+++ b/runtime/native/dalvik_system_VMDebug.cc
@@ -234,9 +234,8 @@
                                            jboolean countAssignable) {
   ScopedObjectAccess soa(env);
   gc::Heap* heap = Runtime::Current()->GetHeap();
-  // We only want reachable instances, so do a GC. This also ensures that the alloc stack
-  // is empty, so the live bitmap is the only place we need to look. Need to do GC before decoding
-  // any jobjects.
+  // We only want reachable instances, so do a GC. Heap::VisitObjects visits all of the heap
+  // objects in the all spaces and the allocation stack.
   heap->CollectGarbage(false);
   mirror::Class* c = soa.Decode<mirror::Class*>(javaClass);
   if (c == nullptr) {
diff --git a/runtime/native/dalvik_system_VMRuntime.cc b/runtime/native/dalvik_system_VMRuntime.cc
index e1b5f97..5267069 100644
--- a/runtime/native/dalvik_system_VMRuntime.cc
+++ b/runtime/native/dalvik_system_VMRuntime.cc
@@ -181,11 +181,12 @@
 
 typedef std::map<std::string, mirror::String*> StringTable;
 
-static mirror::Object* PreloadDexCachesStringsVisitor(mirror::Object* root, void* arg)
+static mirror::Object* PreloadDexCachesStringsCallback(mirror::Object* root, void* arg,
+                                                       uint32_t /*thread_id*/,
+                                                       RootType /*root_type*/)
     SHARED_LOCKS_REQUIRED(Locks::mutator_lock_) {
   StringTable& table = *reinterpret_cast<StringTable*>(arg);
   mirror::String* string = const_cast<mirror::Object*>(root)->AsString();
-  // LOG(INFO) << "VMRuntime.preloadDexCaches interned=" << string->ToModifiedUtf8();
   table[string->ToModifiedUtf8()] = string;
   return root;
 }
@@ -404,7 +405,7 @@
   // We use a std::map to avoid heap allocating StringObjects to lookup in gDvm.literalStrings
   StringTable strings;
   if (kPreloadDexCachesStrings) {
-    runtime->GetInternTable()->VisitRoots(PreloadDexCachesStringsVisitor, &strings, false, false);
+    runtime->GetInternTable()->VisitRoots(PreloadDexCachesStringsCallback, &strings, false, false);
   }
 
   const std::vector<const DexFile*>& boot_class_path = linker->GetBootClassPath();
diff --git a/runtime/object_callbacks.h b/runtime/object_callbacks.h
new file mode 100644
index 0000000..8e3c529
--- /dev/null
+++ b/runtime/object_callbacks.h
@@ -0,0 +1,66 @@
+/*
+ * Copyright (C) 2013 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef ART_RUNTIME_OBJECT_CALLBACKS_H_
+#define ART_RUNTIME_OBJECT_CALLBACKS_H_
+
+// For uint32_t.
+#include <stdint.h>
+// For size_t.
+#include <stdlib.h>
+
+namespace art {
+namespace mirror {
+class Object;
+}  // namespace mirror
+class StackVisitor;
+
+enum RootType {
+  kRootUnknown = 0,
+  kRootJNIGlobal,
+  kRootJNILocal,
+  kRootJavaFrame,
+  kRootNativeStack,
+  kRootStickyClass,
+  kRootThreadBlock,
+  kRootMonitorUsed,
+  kRootThreadObject,
+  kRootInternedString,
+  kRootDebugger,
+  kRootVMInternal,
+  kRootJNIMonitor,
+};
+
+// Returns the new address of the object, returns root if it has not moved. tid and root_type are
+// only used by hprof.
+typedef mirror::Object* (RootCallback)(mirror::Object* root, void* arg, uint32_t thread_id,
+    RootType root_type) __attribute__((warn_unused_result));
+// A callback for visiting an object in the heap.
+typedef void (ObjectCallback)(mirror::Object* obj, void* arg);
+// A callback used for marking an object, returns the new address of the object if the object moved.
+typedef mirror::Object* (MarkObjectCallback)(mirror::Object* obj, void* arg)
+    __attribute__((warn_unused_result));
+// A callback for verifying roots.
+typedef void (VerifyRootCallback)(const mirror::Object* root, void* arg, size_t vreg,
+    const StackVisitor* visitor);
+// A callback for testing if an object is marked, returns nullptr if not marked, otherwise the new
+// address the object (if the object didn't move, returns the object input parameter).
+typedef mirror::Object* (IsMarkedCallback)(mirror::Object* object, void* arg)
+    __attribute__((warn_unused_result));
+
+}  // namespace art
+
+#endif  // ART_RUNTIME_OBJECT_CALLBACKS_H_
diff --git a/runtime/reference_table.cc b/runtime/reference_table.cc
index b5ef735..a9b17e0 100644
--- a/runtime/reference_table.cc
+++ b/runtime/reference_table.cc
@@ -231,9 +231,10 @@
   DumpSummaryLine(os, sorted_entries.back(), GetElementCount(sorted_entries.back()), identical, equiv);
 }
 
-void ReferenceTable::VisitRoots(RootVisitor* visitor, void* arg) {
+void ReferenceTable::VisitRoots(RootCallback* visitor, void* arg, uint32_t tid,
+                                RootType root_type) {
   for (auto& ref : entries_) {
-    ref = visitor(ref, arg);
+    ref = visitor(ref, arg, tid, root_type);
   }
 }
 
diff --git a/runtime/reference_table.h b/runtime/reference_table.h
index 37b3172..c9f5bc5 100644
--- a/runtime/reference_table.h
+++ b/runtime/reference_table.h
@@ -22,8 +22,8 @@
 #include <string>
 #include <vector>
 
+#include "object_callbacks.h"
 #include "locks.h"
-#include "root_visitor.h"
 
 namespace art {
 namespace mirror {
@@ -47,7 +47,7 @@
 
   void Dump(std::ostream& os) const SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
 
-  void VisitRoots(RootVisitor* visitor, void* arg);
+  void VisitRoots(RootCallback* visitor, void* arg, uint32_t tid, RootType root_type);
 
  private:
   typedef std::vector<mirror::Object*> Table;
diff --git a/runtime/root_visitor.h b/runtime/root_visitor.h
deleted file mode 100644
index 78c30ff..0000000
--- a/runtime/root_visitor.h
+++ /dev/null
@@ -1,39 +0,0 @@
-/*
- * Copyright (C) 2013 The Android Open Source Project
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *      http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-
-#ifndef ART_RUNTIME_ROOT_VISITOR_H_
-#define ART_RUNTIME_ROOT_VISITOR_H_
-
-// For size_t.
-#include <stdlib.h>
-
-namespace art {
-namespace mirror {
-class Object;
-}  // namespace mirror
-class StackVisitor;
-
-// Returns the new address of the object, returns root if it has not moved.
-typedef mirror::Object* (RootVisitor)(mirror::Object* root, void* arg)
-    __attribute__((warn_unused_result));
-typedef void (VerifyRootVisitor)(const mirror::Object* root, void* arg, size_t vreg,
-                                 const StackVisitor* visitor);
-typedef bool (IsMarkedTester)(const mirror::Object* object, void* arg);
-typedef void (ObjectVisitorCallback)(mirror::Object* obj, void* arg);
-
-}  // namespace art
-
-#endif  // ART_RUNTIME_ROOT_VISITOR_H_
diff --git a/runtime/runtime.cc b/runtime/runtime.cc
index 09d05d1..9193be5 100644
--- a/runtime/runtime.cc
+++ b/runtime/runtime.cc
@@ -375,7 +375,7 @@
   return value;
 }
 
-void Runtime::SweepSystemWeaks(RootVisitor* visitor, void* arg) {
+void Runtime::SweepSystemWeaks(IsMarkedCallback* visitor, void* arg) {
   GetInternTable()->SweepInternTableWeaks(visitor, arg);
   GetMonitorList()->SweepMonitorList(visitor, arg);
   GetJavaVM()->SweepJniWeakGlobals(visitor, arg);
@@ -1301,66 +1301,69 @@
   return pre_allocated_OutOfMemoryError_;
 }
 
-void Runtime::VisitConcurrentRoots(RootVisitor* visitor, void* arg, bool only_dirty,
+void Runtime::VisitConcurrentRoots(RootCallback* callback, void* arg, bool only_dirty,
                                    bool clean_dirty) {
-  intern_table_->VisitRoots(visitor, arg, only_dirty, clean_dirty);
-  class_linker_->VisitRoots(visitor, arg, only_dirty, clean_dirty);
+  intern_table_->VisitRoots(callback, arg, only_dirty, clean_dirty);
+  class_linker_->VisitRoots(callback, arg, only_dirty, clean_dirty);
 }
 
-void Runtime::VisitNonThreadRoots(RootVisitor* visitor, void* arg) {
+void Runtime::VisitNonThreadRoots(RootCallback* callback, void* arg) {
   // Visit the classes held as static in mirror classes.
-  mirror::ArtField::VisitRoots(visitor, arg);
-  mirror::ArtMethod::VisitRoots(visitor, arg);
-  mirror::Class::VisitRoots(visitor, arg);
-  mirror::StackTraceElement::VisitRoots(visitor, arg);
-  mirror::String::VisitRoots(visitor, arg);
-  mirror::Throwable::VisitRoots(visitor, arg);
+  mirror::ArtField::VisitRoots(callback, arg);
+  mirror::ArtMethod::VisitRoots(callback, arg);
+  mirror::Class::VisitRoots(callback, arg);
+  mirror::StackTraceElement::VisitRoots(callback, arg);
+  mirror::String::VisitRoots(callback, arg);
+  mirror::Throwable::VisitRoots(callback, arg);
   // Visit all the primitive array types classes.
-  mirror::PrimitiveArray<uint8_t>::VisitRoots(visitor, arg);   // BooleanArray
-  mirror::PrimitiveArray<int8_t>::VisitRoots(visitor, arg);    // ByteArray
-  mirror::PrimitiveArray<uint16_t>::VisitRoots(visitor, arg);  // CharArray
-  mirror::PrimitiveArray<double>::VisitRoots(visitor, arg);    // DoubleArray
-  mirror::PrimitiveArray<float>::VisitRoots(visitor, arg);     // FloatArray
-  mirror::PrimitiveArray<int32_t>::VisitRoots(visitor, arg);   // IntArray
-  mirror::PrimitiveArray<int64_t>::VisitRoots(visitor, arg);   // LongArray
-  mirror::PrimitiveArray<int16_t>::VisitRoots(visitor, arg);   // ShortArray
-  java_vm_->VisitRoots(visitor, arg);
+  mirror::PrimitiveArray<uint8_t>::VisitRoots(callback, arg);   // BooleanArray
+  mirror::PrimitiveArray<int8_t>::VisitRoots(callback, arg);    // ByteArray
+  mirror::PrimitiveArray<uint16_t>::VisitRoots(callback, arg);  // CharArray
+  mirror::PrimitiveArray<double>::VisitRoots(callback, arg);    // DoubleArray
+  mirror::PrimitiveArray<float>::VisitRoots(callback, arg);     // FloatArray
+  mirror::PrimitiveArray<int32_t>::VisitRoots(callback, arg);   // IntArray
+  mirror::PrimitiveArray<int64_t>::VisitRoots(callback, arg);   // LongArray
+  mirror::PrimitiveArray<int16_t>::VisitRoots(callback, arg);   // ShortArray
+  java_vm_->VisitRoots(callback, arg);
   if (pre_allocated_OutOfMemoryError_ != nullptr) {
     pre_allocated_OutOfMemoryError_ = down_cast<mirror::Throwable*>(
-        visitor(pre_allocated_OutOfMemoryError_, arg));
+        callback(pre_allocated_OutOfMemoryError_, arg, 0, kRootVMInternal));
     DCHECK(pre_allocated_OutOfMemoryError_ != nullptr);
   }
-  resolution_method_ = down_cast<mirror::ArtMethod*>(visitor(resolution_method_, arg));
+  resolution_method_ = down_cast<mirror::ArtMethod*>(callback(resolution_method_, arg, 0,
+                                                              kRootVMInternal));
   DCHECK(resolution_method_ != nullptr);
   if (HasImtConflictMethod()) {
-    imt_conflict_method_ = down_cast<mirror::ArtMethod*>(visitor(imt_conflict_method_, arg));
+    imt_conflict_method_ = down_cast<mirror::ArtMethod*>(callback(imt_conflict_method_, arg, 0,
+                                                                  kRootVMInternal));
   }
   if (HasDefaultImt()) {
-    default_imt_ = down_cast<mirror::ObjectArray<mirror::ArtMethod>*>(visitor(default_imt_, arg));
+    default_imt_ = down_cast<mirror::ObjectArray<mirror::ArtMethod>*>(callback(default_imt_, arg,
+                                                                               0, kRootVMInternal));
   }
 
   for (int i = 0; i < Runtime::kLastCalleeSaveType; i++) {
     if (callee_save_methods_[i] != nullptr) {
       callee_save_methods_[i] = down_cast<mirror::ArtMethod*>(
-          visitor(callee_save_methods_[i], arg));
+          callback(callee_save_methods_[i], arg, 0, kRootVMInternal));
     }
   }
   {
     MutexLock mu(Thread::Current(), method_verifiers_lock_);
     for (verifier::MethodVerifier* verifier : method_verifiers_) {
-      verifier->VisitRoots(visitor, arg);
+      verifier->VisitRoots(callback, arg);
     }
   }
 }
 
-void Runtime::VisitNonConcurrentRoots(RootVisitor* visitor, void* arg) {
-  thread_list_->VisitRoots(visitor, arg);
-  VisitNonThreadRoots(visitor, arg);
+void Runtime::VisitNonConcurrentRoots(RootCallback* callback, void* arg) {
+  thread_list_->VisitRoots(callback, arg);
+  VisitNonThreadRoots(callback, arg);
 }
 
-void Runtime::VisitRoots(RootVisitor* visitor, void* arg, bool only_dirty, bool clean_dirty) {
-  VisitConcurrentRoots(visitor, arg, only_dirty, clean_dirty);
-  VisitNonConcurrentRoots(visitor, arg);
+void Runtime::VisitRoots(RootCallback* callback, void* arg, bool only_dirty, bool clean_dirty) {
+  VisitConcurrentRoots(callback, arg, only_dirty, clean_dirty);
+  VisitNonConcurrentRoots(callback, arg);
 }
 
 mirror::ObjectArray<mirror::ArtMethod>* Runtime::CreateDefaultImt(ClassLinker* cl) {
diff --git a/runtime/runtime.h b/runtime/runtime.h
index 896a18b..07f3d7d 100644
--- a/runtime/runtime.h
+++ b/runtime/runtime.h
@@ -34,7 +34,7 @@
 #include "instrumentation.h"
 #include "jobject_comparator.h"
 #include "locks.h"
-#include "root_visitor.h"
+#include "object_callbacks.h"
 #include "runtime_stats.h"
 #include "safe_map.h"
 
@@ -341,24 +341,24 @@
 
   // Visit all the roots. If only_dirty is true then non-dirty roots won't be visited. If
   // clean_dirty is true then dirty roots will be marked as non-dirty after visiting.
-  void VisitRoots(RootVisitor* visitor, void* arg, bool only_dirty, bool clean_dirty)
+  void VisitRoots(RootCallback* visitor, void* arg, bool only_dirty, bool clean_dirty)
       SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
 
   // Visit all of the roots we can do safely do concurrently.
-  void VisitConcurrentRoots(RootVisitor* visitor, void* arg, bool only_dirty, bool clean_dirty)
+  void VisitConcurrentRoots(RootCallback* visitor, void* arg, bool only_dirty, bool clean_dirty)
       SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
 
   // Visit all of the non thread roots, we can do this with mutators unpaused.
-  void VisitNonThreadRoots(RootVisitor* visitor, void* arg)
+  void VisitNonThreadRoots(RootCallback* visitor, void* arg)
       SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
 
   // Visit all other roots which must be done with mutators suspended.
-  void VisitNonConcurrentRoots(RootVisitor* visitor, void* arg)
+  void VisitNonConcurrentRoots(RootCallback* visitor, void* arg)
       SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
 
   // Sweep system weaks, the system weak is deleted if the visitor return nullptr. Otherwise, the
   // system weak is updated to be the visitor's returned value.
-  void SweepSystemWeaks(RootVisitor* visitor, void* arg)
+  void SweepSystemWeaks(IsMarkedCallback* visitor, void* arg)
       SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
 
   // Returns a special method that calls into a trampoline for runtime method resolution
diff --git a/runtime/thread.cc b/runtime/thread.cc
index c649765..b5320ca 100644
--- a/runtime/thread.cc
+++ b/runtime/thread.cc
@@ -992,7 +992,8 @@
   }
 }
 
-static mirror::Object* MonitorExitVisitor(mirror::Object* object, void* arg)
+static mirror::Object* MonitorExitVisitor(mirror::Object* object, void* arg, uint32_t /*thread_id*/,
+                                          RootType /*root_type*/)
     NO_THREAD_SAFETY_ANALYSIS {
   Thread* self = reinterpret_cast<Thread*>(arg);
   mirror::Object* entered_monitor = object;
@@ -1034,7 +1035,7 @@
 
   // On thread detach, all monitors entered with JNI MonitorEnter are automatically exited.
   if (jni_env_ != nullptr) {
-    jni_env_->monitors.VisitRoots(MonitorExitVisitor, self);
+    jni_env_->monitors.VisitRoots(MonitorExitVisitor, self, 0, kRootVMInternal);
   }
 }
 
@@ -1144,16 +1145,17 @@
   return managed_stack_.ShadowFramesContain(sirt_entry);
 }
 
-void Thread::SirtVisitRoots(RootVisitor* visitor, void* arg) {
+void Thread::SirtVisitRoots(RootCallback* visitor, void* arg) {
+  uint32_t tid = GetTid();
   for (StackIndirectReferenceTable* cur = top_sirt_; cur; cur = cur->GetLink()) {
     size_t num_refs = cur->NumberOfReferences();
     for (size_t j = 0; j < num_refs; ++j) {
       mirror::Object* object = cur->GetReference(j);
       if (object != nullptr) {
-        const mirror::Object* new_obj = visitor(object, arg);
+        mirror::Object* new_obj = visitor(object, arg, tid, kRootNativeStack);
         DCHECK(new_obj != nullptr);
         if (new_obj != object) {
-          cur->SetReference(j, const_cast<mirror::Object*>(new_obj));
+          cur->SetReference(j, new_obj);
         }
       }
     }
@@ -1954,31 +1956,17 @@
 
 class RootCallbackVisitor {
  public:
-  RootCallbackVisitor(RootVisitor* visitor, void* arg) : visitor_(visitor), arg_(arg) {}
+  RootCallbackVisitor(RootCallback* callback, void* arg, uint32_t tid)
+     : callback_(callback), arg_(arg), tid_(tid) {}
 
   mirror::Object* operator()(mirror::Object* obj, size_t, const StackVisitor*) const {
-    return visitor_(obj, arg_);
+    return callback_(obj, arg_, tid_, kRootJavaFrame);
   }
 
  private:
-  RootVisitor* visitor_;
-  void* arg_;
-};
-
-class VerifyCallbackVisitor {
- public:
-  VerifyCallbackVisitor(VerifyRootVisitor* visitor, void* arg)
-      : visitor_(visitor),
-        arg_(arg) {
-  }
-
-  void operator()(const mirror::Object* obj, size_t vreg, const StackVisitor* visitor) const {
-    visitor_(obj, arg_, vreg, visitor);
-  }
-
- private:
-  VerifyRootVisitor* const visitor_;
+  RootCallback* const callback_;
   void* const arg_;
+  const uint32_t tid_;
 };
 
 void Thread::SetClassLoaderOverride(mirror::ClassLoader* class_loader_override) {
@@ -1988,39 +1976,42 @@
   class_loader_override_ = class_loader_override;
 }
 
-void Thread::VisitRoots(RootVisitor* visitor, void* arg) {
+void Thread::VisitRoots(RootCallback* visitor, void* arg) {
+  uint32_t thread_id = GetThreadId();
   if (opeer_ != nullptr) {
-    opeer_ = visitor(opeer_, arg);
+    opeer_ = visitor(opeer_, arg, thread_id, kRootThreadObject);
   }
   if (exception_ != nullptr) {
-    exception_ = down_cast<mirror::Throwable*>(visitor(exception_, arg));
+    exception_ = down_cast<mirror::Throwable*>(visitor(exception_, arg, thread_id,
+                                                       kRootNativeStack));
   }
   throw_location_.VisitRoots(visitor, arg);
   if (class_loader_override_ != nullptr) {
-    class_loader_override_ = down_cast<mirror::ClassLoader*>(visitor(class_loader_override_, arg));
+    class_loader_override_ =
+        down_cast<mirror::ClassLoader*>(visitor(class_loader_override_, arg, thread_id,
+                                                kRootNativeStack));
   }
-  jni_env_->locals.VisitRoots(visitor, arg);
-  jni_env_->monitors.VisitRoots(visitor, arg);
-
+  jni_env_->locals.VisitRoots(visitor, arg, thread_id, kRootJNILocal);
+  jni_env_->monitors.VisitRoots(visitor, arg, thread_id, kRootJNIMonitor);
   SirtVisitRoots(visitor, arg);
-
   // Visit roots on this thread's stack
   Context* context = GetLongJumpContext();
-  RootCallbackVisitor visitorToCallback(visitor, arg);
+  RootCallbackVisitor visitorToCallback(visitor, arg, thread_id);
   ReferenceMapVisitor<RootCallbackVisitor> mapper(this, context, visitorToCallback);
   mapper.WalkStack();
   ReleaseLongJumpContext(context);
-
   for (instrumentation::InstrumentationStackFrame& frame : *GetInstrumentationStack()) {
     if (frame.this_object_ != nullptr) {
-      frame.this_object_ = visitor(frame.this_object_, arg);
+      frame.this_object_ = visitor(frame.this_object_, arg, thread_id, kRootJavaFrame);
     }
     DCHECK(frame.method_ != nullptr);
-    frame.method_ = down_cast<mirror::ArtMethod*>(visitor(frame.method_, arg));
+    frame.method_ = down_cast<mirror::ArtMethod*>(visitor(frame.method_, arg, thread_id,
+                                                          kRootJavaFrame));
   }
 }
 
-static mirror::Object* VerifyRoot(mirror::Object* root, void* arg) {
+static mirror::Object* VerifyRoot(mirror::Object* root, void* arg, uint32_t /*thread_id*/,
+                                  RootType /*root_type*/) {
   DCHECK(root != nullptr);
   DCHECK(arg != nullptr);
   reinterpret_cast<gc::Heap*>(arg)->VerifyObject(root);
@@ -2029,7 +2020,7 @@
 
 void Thread::VerifyStackImpl() {
   UniquePtr<Context> context(Context::Create());
-  RootCallbackVisitor visitorToCallback(VerifyRoot, Runtime::Current()->GetHeap());
+  RootCallbackVisitor visitorToCallback(VerifyRoot, Runtime::Current()->GetHeap(), GetTid());
   ReferenceMapVisitor<RootCallbackVisitor> mapper(this, context.get(), visitorToCallback);
   mapper.WalkStack();
 }
diff --git a/runtime/thread.h b/runtime/thread.h
index b7f8bb0..daffc92 100644
--- a/runtime/thread.h
+++ b/runtime/thread.h
@@ -31,8 +31,8 @@
 #include "globals.h"
 #include "jvalue.h"
 #include "locks.h"
+#include "object_callbacks.h"
 #include "offsets.h"
-#include "root_visitor.h"
 #include "runtime_stats.h"
 #include "stack.h"
 #include "stack_indirect_reference_table.h"
@@ -389,7 +389,7 @@
   static jobjectArray InternalStackTraceToStackTraceElementArray(JNIEnv* env, jobject internal,
       jobjectArray output_array = NULL, int* stack_depth = NULL);
 
-  void VisitRoots(RootVisitor* visitor, void* arg) SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
+  void VisitRoots(RootCallback* visitor, void* arg) SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
 
   void VerifyStack() SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
 
@@ -503,7 +503,8 @@
   // Is the given obj in this thread's stack indirect reference table?
   bool SirtContains(jobject obj) const;
 
-  void SirtVisitRoots(RootVisitor* visitor, void* arg) SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
+  void SirtVisitRoots(RootCallback* visitor, void* arg)
+      SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
 
   void PushSirt(StackIndirectReferenceTable* sirt) {
     sirt->SetLink(top_sirt_);
diff --git a/runtime/thread_list.cc b/runtime/thread_list.cc
index 8bf099b..25f692d 100644
--- a/runtime/thread_list.cc
+++ b/runtime/thread_list.cc
@@ -756,28 +756,30 @@
   }
 }
 
-void ThreadList::VisitRoots(RootVisitor* visitor, void* arg) const {
+void ThreadList::VisitRoots(RootCallback* callback, void* arg) const {
   MutexLock mu(Thread::Current(), *Locks::thread_list_lock_);
   for (const auto& thread : list_) {
-    thread->VisitRoots(visitor, arg);
+    thread->VisitRoots(callback, arg);
   }
 }
 
-struct VerifyRootWrapperArg {
-  VerifyRootVisitor* visitor;
-  void* arg;
+class VerifyRootWrapperArg {
+ public:
+  VerifyRootWrapperArg(VerifyRootCallback* callback, void* arg) : callback_(callback), arg_(arg) {
+  }
+  VerifyRootCallback* const callback_;
+  void* const arg_;
 };
 
-static mirror::Object* VerifyRootWrapperCallback(mirror::Object* root, void* arg) {
+static mirror::Object* VerifyRootWrapperCallback(mirror::Object* root, void* arg,
+                                                 uint32_t /*thread_id*/, RootType /*root_type*/) {
   VerifyRootWrapperArg* wrapperArg = reinterpret_cast<VerifyRootWrapperArg*>(arg);
-  wrapperArg->visitor(root, wrapperArg->arg, 0, NULL);
+  wrapperArg->callback_(root, wrapperArg->arg_, 0, NULL);
   return root;
 }
 
-void ThreadList::VerifyRoots(VerifyRootVisitor* visitor, void* arg) const {
-  VerifyRootWrapperArg wrapper;
-  wrapper.visitor = visitor;
-  wrapper.arg = arg;
+void ThreadList::VerifyRoots(VerifyRootCallback* callback, void* arg) const {
+  VerifyRootWrapperArg wrapper(callback, arg);
   MutexLock mu(Thread::Current(), *Locks::thread_list_lock_);
   for (const auto& thread : list_) {
     thread->VisitRoots(VerifyRootWrapperCallback, &wrapper);
diff --git a/runtime/thread_list.h b/runtime/thread_list.h
index 45994ae..e98aed9 100644
--- a/runtime/thread_list.h
+++ b/runtime/thread_list.h
@@ -19,7 +19,7 @@
 
 #include "base/mutex.h"
 #include "jni.h"
-#include "root_visitor.h"
+#include "object_callbacks.h"
 
 #include <bitset>
 #include <list>
@@ -113,10 +113,10 @@
       LOCKS_EXCLUDED(Locks::mutator_lock_, Locks::thread_list_lock_);
   void Unregister(Thread* self) LOCKS_EXCLUDED(Locks::mutator_lock_, Locks::thread_list_lock_);
 
-  void VisitRoots(RootVisitor* visitor, void* arg) const
+  void VisitRoots(RootCallback* callback, void* arg) const
       SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
 
-  void VerifyRoots(VerifyRootVisitor* visitor, void* arg) const
+  void VerifyRoots(VerifyRootCallback* callback, void* arg) const
       SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
 
   // Return a copy of the thread list.
diff --git a/runtime/throw_location.cc b/runtime/throw_location.cc
index 1cc3e74..2a1faff 100644
--- a/runtime/throw_location.cc
+++ b/runtime/throw_location.cc
@@ -33,13 +33,13 @@
   }
 }
 
-void ThrowLocation::VisitRoots(RootVisitor* visitor, void* arg) {
+void ThrowLocation::VisitRoots(RootCallback* visitor, void* arg) {
   if (this_object_ != nullptr) {
-    this_object_ = visitor(this_object_, arg);
+    this_object_ = visitor(this_object_, arg, 0, kRootVMInternal);
     DCHECK(this_object_ != nullptr);
   }
   if (method_ != nullptr) {
-    method_ = down_cast<mirror::ArtMethod*>(visitor(method_, arg));
+    method_ = down_cast<mirror::ArtMethod*>(visitor(method_, arg, 0, kRootVMInternal));
     DCHECK(method_ != nullptr);
   }
 }
diff --git a/runtime/throw_location.h b/runtime/throw_location.h
index 5da446e..f30aa4e 100644
--- a/runtime/throw_location.h
+++ b/runtime/throw_location.h
@@ -17,8 +17,8 @@
 #ifndef ART_RUNTIME_THROW_LOCATION_H_
 #define ART_RUNTIME_THROW_LOCATION_H_
 
+#include "object_callbacks.h"
 #include "base/macros.h"
-#include "root_visitor.h"
 
 #include <stdint.h>
 #include <string>
@@ -62,7 +62,7 @@
 
   std::string Dump() const SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
 
-  void VisitRoots(RootVisitor* visitor, void* arg);
+  void VisitRoots(RootCallback* visitor, void* arg);
 
  private:
   // The 'this' reference of the throwing method.
diff --git a/runtime/verifier/method_verifier.cc b/runtime/verifier/method_verifier.cc
index 30be36c..ab943a6 100644
--- a/runtime/verifier/method_verifier.cc
+++ b/runtime/verifier/method_verifier.cc
@@ -3983,8 +3983,8 @@
   verifier::RegTypeCache::ShutDown();
 }
 
-void MethodVerifier::VisitRoots(RootVisitor* visitor, void* arg) {
-  reg_types_.VisitRoots(visitor, arg);
+void MethodVerifier::VisitRoots(RootCallback* callback, void* arg) {
+  reg_types_.VisitRoots(callback, arg);
 }
 
 }  // namespace verifier
diff --git a/runtime/verifier/method_verifier.h b/runtime/verifier/method_verifier.h
index 7c75c9c..031cfec 100644
--- a/runtime/verifier/method_verifier.h
+++ b/runtime/verifier/method_verifier.h
@@ -220,7 +220,7 @@
   // Describe VRegs at the given dex pc.
   std::vector<int32_t> DescribeVRegs(uint32_t dex_pc);
 
-  void VisitRoots(RootVisitor* visitor, void* arg) SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
+  void VisitRoots(RootCallback* callback, void* arg) SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
 
   // Accessors used by the compiler via CompilerCallback
   const DexFile::CodeItem* CodeItem() const;
diff --git a/runtime/verifier/reg_type.cc b/runtime/verifier/reg_type.cc
index f394bce..e56e670 100644
--- a/runtime/verifier/reg_type.cc
+++ b/runtime/verifier/reg_type.cc
@@ -969,9 +969,9 @@
   }
 }
 
-void RegType::VisitRoots(RootVisitor* visitor, void* arg) {
+void RegType::VisitRoots(RootCallback* callback, void* arg) {
   if (klass_ != nullptr) {
-    klass_ = down_cast<mirror::Class*>(visitor(klass_, arg));
+    klass_ = down_cast<mirror::Class*>(callback(klass_, arg, 0, kRootUnknown));
   }
 }
 
diff --git a/runtime/verifier/reg_type.h b/runtime/verifier/reg_type.h
index 3818375..a23b8c4 100644
--- a/runtime/verifier/reg_type.h
+++ b/runtime/verifier/reg_type.h
@@ -19,8 +19,8 @@
 
 #include "base/macros.h"
 #include "globals.h"
+#include "object_callbacks.h"
 #include "primitive.h"
-#include "root_visitor.h"
 
 #include "jni.h"
 
@@ -270,7 +270,7 @@
 
   virtual ~RegType() {}
 
-  void VisitRoots(RootVisitor* visitor, void* arg) SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
+  void VisitRoots(RootCallback* callback, void* arg) SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
 
  protected:
   RegType(mirror::Class* klass, const std::string& descriptor, uint16_t cache_id)
diff --git a/runtime/verifier/reg_type_cache.cc b/runtime/verifier/reg_type_cache.cc
index c8a03d6..5e894ed 100644
--- a/runtime/verifier/reg_type_cache.cc
+++ b/runtime/verifier/reg_type_cache.cc
@@ -573,9 +573,9 @@
   }
 }
 
-void RegTypeCache::VisitRoots(RootVisitor* visitor, void* arg) {
+void RegTypeCache::VisitRoots(RootCallback* callback, void* arg) {
   for (RegType* entry : entries_) {
-    entry->VisitRoots(visitor, arg);
+    entry->VisitRoots(callback, arg);
   }
 }
 
diff --git a/runtime/verifier/reg_type_cache.h b/runtime/verifier/reg_type_cache.h
index 41bc8c9..4cc7e61 100644
--- a/runtime/verifier/reg_type_cache.h
+++ b/runtime/verifier/reg_type_cache.h
@@ -20,8 +20,8 @@
 #include "base/casts.h"
 #include "base/macros.h"
 #include "base/stl_util.h"
+#include "object_callbacks.h"
 #include "reg_type.h"
-#include "root_visitor.h"
 #include "runtime.h"
 
 #include <stdint.h>
@@ -146,7 +146,7 @@
   void Dump(std::ostream& os) SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
   const RegType& RegTypeFromPrimitiveType(Primitive::Type) const;
 
-  void VisitRoots(RootVisitor* visitor, void* arg) SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
+  void VisitRoots(RootCallback* callback, void* arg) SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
 
  private:
   void FillPrimitiveAndSmallConstantTypes() SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);