Safer interface for heap iteration.

runtime/vm/heap.h

Index: runtime/vm/heap.h
diff --git a/runtime/vm/heap.h b/runtime/vm/heap.h
index 6d8752ca98d3ddd8b27f1762578daf030f13b968..43858837d33cfb7ea2bf7aeddaa5614f3a84cc77 100644
--- a/runtime/vm/heap.h
+++ b/runtime/vm/heap.h
@@ -105,14 +105,9 @@ class Heap {
   bool CodeContains(uword addr) const;
   bool StubCodeContains(uword addr) const;
 
-  // Visit all pointers. Caller must ensure concurrent sweeper is not running,
-  // and the visitor must not allocate (see issue 21620).
-  void VisitObjectPointers(ObjectPointerVisitor* visitor) const;
-
-  // Visit all objects, including FreeListElement "objects". Caller must ensure
-  // concurrent sweeper is not running, and the visitor must not allocate (see
-  // issue 21620).
-  void VisitObjects(ObjectVisitor* visitor) const;
+  void IterateObjects(ObjectVisitor* visitor) const;
+  void IterateOldObjects(ObjectVisitor* visitor) const;
+  void IterateObjectPointers(ObjectVisitor* visitor) const;
 
   // Find an object by visiting all pointers in the specified heap space,
   // the 'visitor' is used to determine if an object is found or not.
@@ -121,8 +116,7 @@ class Heap {
   // point.
   // The 'visitor' function should return false if the object is not found,
   // traversal through the heap space continues.
-  // Returns null object if nothing is found. Must be called within a
-  // NoSafepointScope.
+  // Returns null object if nothing is found.
   RawInstructions* FindObjectInCodeSpace(FindObjectVisitor* visitor) const;
   RawObject* FindOldObject(FindObjectVisitor* visitor) const;
   RawObject* FindNewObject(FindObjectVisitor* visitor) const;
@@ -284,6 +278,18 @@ class Heap {
   uword AllocateOld(intptr_t size, HeapPage::PageType type);
   uword AllocatePretenured(intptr_t size);
 
+  // Visit all pointers. Caller must ensure concurrent sweeper is not running,
+  // and the visitor must not allocate.
+  void VisitObjectPointers(ObjectPointerVisitor* visitor) const;
+
+  // Visit all objects, including FreeListElement "objects". Caller must ensure
+  // concurrent sweeper is not running, and the visitor must not allocate.
+  void VisitObjects(ObjectVisitor* visitor) const;
+
+  // Like Verify, but does not wait for concurrent sweeper, so caller must
+  // ensure thread-safety.
+  bool VerifyGC(MarkExpectation mark_expectation = kForbidMarked) const;
+
   // GC stats collection.
   void RecordBeforeGC(Space space, GCReason reason);
   void RecordAfterGC();
@@ -318,6 +324,7 @@ class Heap {
 
   friend class ServiceEvent;
   friend class GCTestHelper;
+  friend class PageSpace;  // VerifyGC
   DISALLOW_COPY_AND_ASSIGN(Heap);
 };
 
@@ -342,6 +349,18 @@ class NoSafepointScope : public ValueObject {
 #endif  // defined(DEBUG)
 
 
+class HeapIterationScope : public StackResource {
+ public:
+  HeapIterationScope();
+  ~HeapIterationScope();
+ private:
+  NoSafepointScope no_safepoint_scope_;
+  PageSpace* old_space_;
+
+  DISALLOW_COPY_AND_ASSIGN(HeapIterationScope);
+};
+
+
 class NoHeapGrowthControlScope : public StackResource {
  public:
   NoHeapGrowthControlScope();