Heap snapshot: Update user roots definition.

Do not define an object as a user root if its context is not
present in Global handles.

R=mstarzinger@chromium.org, yurys@chromium.org

Review URL: https://codereview.chromium.org/17881005

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@15381 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/heap-snapshot-generator.cc

@@ -961,7 +961,7 @@ void V8HeapExplorer::ExtractReferences(HeapObject* obj) {
 
   bool extract_indexed_refs = true;
   if (obj->IsJSGlobalProxy()) {
-    ExtractJSGlobalProxyReferences(JSGlobalProxy::cast(obj));
+    ExtractJSGlobalProxyReferences(entry, JSGlobalProxy::cast(obj));
   } else if (obj->IsJSObject()) {
     ExtractJSObjectReferences(entry, JSObject::cast(obj));
   } else if (obj->IsString()) {
@@ -996,19 +996,11 @@ void V8HeapExplorer::ExtractReferences(HeapObject* obj) {
 }
 
 
-void V8HeapExplorer::ExtractJSGlobalProxyReferences(JSGlobalProxy* proxy) {
-  // We need to reference JS global objects from snapshot's root.
-  // We use JSGlobalProxy because this is what embedder (e.g. browser)
-  // uses for the global object.
-  Object* object = proxy->map()->prototype();
-  bool is_debug_object = false;
-#ifdef ENABLE_DEBUGGER_SUPPORT
-  is_debug_object = object->IsGlobalObject() &&
-      Isolate::Current()->debug()->IsDebugGlobal(GlobalObject::cast(object));
-#endif
-  if (!is_debug_object) {
-    SetUserGlobalReference(object);
-  }
+void V8HeapExplorer::ExtractJSGlobalProxyReferences(
+    int entry, JSGlobalProxy* proxy) {
+  SetInternalReference(proxy, entry,
+                       "native_context", proxy->native_context(),
+                       JSGlobalProxy::kNativeContextOffset);
 }
 
 
@@ -1778,6 +1770,22 @@ void V8HeapExplorer::SetGcSubrootReference(
           snapshot_->gc_subroot(tag)->index(),
           child_entry);
     }
+
+    // Add a shortcut to JS global object reference at snapshot root.
+    if (child_obj->IsNativeContext()) {
+      Context* context = Context::cast(child_obj);
+      GlobalObject* global = context->global_object();
+      if (global->IsJSGlobalObject()) {
+        bool is_debug_object = false;
+#ifdef ENABLE_DEBUGGER_SUPPORT
+        is_debug_object = heap_->isolate()->debug()->IsDebugGlobal(global);
+#endif
+        if (!is_debug_object && !user_roots_.Contains(global)) {
+          user_roots_.Insert(global);
+          SetUserGlobalReference(global);
+        }
+      }
+    }
   }
 }
 

src/heap-snapshot-generator.h

@@ -454,7 +454,7 @@ class V8HeapExplorer : public HeapEntriesAllocator {
   const char* GetSystemEntryName(HeapObject* object);
 
   void ExtractReferences(HeapObject* obj);
-  void ExtractJSGlobalProxyReferences(JSGlobalProxy* proxy);
+  void ExtractJSGlobalProxyReferences(int entry, JSGlobalProxy* proxy);
   void ExtractJSObjectReferences(int entry, JSObject* js_obj);
   void ExtractStringReferences(int entry, String* obj);
   void ExtractContextReferences(int entry, Context* context);
@@ -532,6 +532,7 @@ class V8HeapExplorer : public HeapEntriesAllocator {
   SnapshotFillerInterface* filler_;
   HeapObjectsSet objects_tags_;
   HeapObjectsSet strong_gc_subroot_names_;
+  HeapObjectsSet user_roots_;
   v8::HeapProfiler::ObjectNameResolver* global_object_name_resolver_;
 
   static HeapObject* const kGcRootsObject;

test/cctest/test-heap-profiler.cc

@@ -92,8 +92,9 @@ class NamedEntriesDetector {
 static const v8::HeapGraphNode* GetGlobalObject(
     const v8::HeapSnapshot* snapshot) {
   CHECK_EQ(2, snapshot->GetRoot()->GetChildrenCount());
+  // The 0th-child is (GC Roots), 1st is the user root.
   const v8::HeapGraphNode* global_obj =
-      snapshot->GetRoot()->GetChild(0)->GetToNode();
+      snapshot->GetRoot()->GetChild(1)->GetToNode();
   CHECK_EQ(0, strncmp("Object", const_cast<i::HeapEntry*>(
       reinterpret_cast<const i::HeapEntry*>(global_obj))->name(), 6));
   return global_obj;
@@ -658,7 +659,8 @@ TEST(HeapSnapshotJSONSerialization) {
       "  first_edge_indexes[i] = first_edge_index;\n"
       "  first_edge_index += edge_fields_count *\n"
       "      parsed.nodes[i * node_fields_count + edge_count_offset];\n"
-      "}\n");
+      "}\n"
+      "first_edge_indexes[node_count] = first_edge_index;\n");
   CHECK(!meta_analysis_result.IsEmpty());
 
   // A helper function for processing encoded nodes.
@@ -682,7 +684,7 @@ TEST(HeapSnapshotJSONSerialization) {
       "GetChildPosByProperty(\n"
       "  GetChildPosByProperty(\n"
       "    GetChildPosByProperty("
-      "      parsed.edges[edge_to_node_offset],"
+      "      parsed.edges[edge_fields_count + edge_to_node_offset],"
       "      \"b\", property_type),\n"
       "    \"x\", property_type),"
       "  \"s\", property_type)");