Add v8::HeapGraphNode::GetHeapValue method.

This allows getting a heap object by a heap snapshot node for further
inspection. Very useful for objects from bindings that mostly have
getter-provided fields.

R=vegorov@google.com
BUG=webkit/61179
TEST=test-heap-profiler/GetHeapValue,GetHeapValueForDeletedObject

Review URL: http://codereview.chromium.org/8046006

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@9430 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

include/v8-profiler.h

@@ -307,6 +307,12 @@ class V8EXPORT HeapGraphNode {
    * path from the snapshot root to the current node.
    */
   const HeapGraphNode* GetDominatorNode() const;
+
+  /**
+   * Finds and returns a value from the heap corresponding to this node,
+   * if the value is still reachable.
+   */
+  Handle<Value> GetHeapValue() const;
 };
 
 

src/api.cc

@@ -5811,6 +5811,16 @@ const HeapGraphNode* HeapGraphNode::GetDominatorNode() const {
 }
 
 
+v8::Handle<v8::Value> HeapGraphNode::GetHeapValue() const {
+  i::Isolate* isolate = i::Isolate::Current();
+  IsDeadCheck(isolate, "v8::HeapGraphNode::GetHeapValue");
+  i::Handle<i::HeapObject> object = ToInternal(this)->GetHeapObject();
+  return v8::Handle<Value>(!object.is_null() ?
+                           ToApi<Value>(object) : ToApi<Value>(
+                               isolate->factory()->undefined_value()));
+}
+
+
 static i::HeapSnapshot* ToInternal(const HeapSnapshot* snapshot) {
   return const_cast<i::HeapSnapshot*>(
       reinterpret_cast<const i::HeapSnapshot*>(snapshot));

src/profile-generator.cc

@@ -1015,6 +1015,11 @@ int HeapEntry::RetainedSize(bool exact) {
 }
 
 
+Handle<HeapObject> HeapEntry::GetHeapObject() {
+  return snapshot_->collection()->FindHeapObjectById(id());
+}
+
+
 template<class Visitor>
 void HeapEntry::ApplyAndPaintAllReachable(Visitor* visitor) {
   List<HeapEntry*> list(10);
@@ -1522,6 +1527,26 @@ void HeapSnapshotsCollection::RemoveSnapshot(HeapSnapshot* snapshot) {
 }
 
 
+Handle<HeapObject> HeapSnapshotsCollection::FindHeapObjectById(uint64_t id) {
+  // First perform a full GC in order to avoid dead objects.
+  HEAP->CollectAllGarbage(Heap::kMakeHeapIterableMask);
+  AssertNoAllocation no_allocation;
+  HeapObject* object = NULL;
+  HeapIterator iterator(HeapIterator::kFilterUnreachable);
+  // Make sure that object with the given id is still reachable.
+  for (HeapObject* obj = iterator.next();
+       obj != NULL;
+       obj = iterator.next()) {
+    if (ids_.FindObject(obj->address()) == id) {
+      ASSERT(object == NULL);
+      object = obj;
+      // Can't break -- kFilterUnreachable requires full heap traversal.
+    }
+  }
+  return object != NULL ? Handle<HeapObject>(object) : Handle<HeapObject>();
+}
+
+
 HeapEntry *const HeapEntriesMap::kHeapEntryPlaceholder =
     reinterpret_cast<HeapEntry*>(1);
 

src/profile-generator.h

@@ -588,6 +588,8 @@ class HeapEntry BASE_EMBEDDED {
 
   void Print(int max_depth, int indent);
 
+  Handle<HeapObject> GetHeapObject();
+
   static int EntriesSize(int entries_count,
                          int children_count,
                          int retainers_count);
@@ -766,6 +768,7 @@ class HeapSnapshotsCollection {
   TokenEnumerator* token_enumerator() { return token_enumerator_; }
 
   uint64_t GetObjectId(Address addr) { return ids_.FindObject(addr); }
+  Handle<HeapObject> FindHeapObjectById(uint64_t id);
   void ObjectMoveEvent(Address from, Address to) { ids_.MoveObject(from, to); }
 
  private: