Distinguish weak references in heap snapshots, group GC roots.

Several changes to better organize snapshot data:

1. Provide information about weak references.
2. Group (GC roots) children.
3. Prettify debug snapshot printing.

BUG=v8:1832
TEST=cctest/test-heap-profiler/*Weak*

Review URL: http://codereview.chromium.org/8716009

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@10158 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

include/v8-profiler.h

@@ -219,8 +219,9 @@ class V8EXPORT HeapGraphEdge {
                            // (e.g. parts of a ConsString).
     kHidden = 4,           // A link that is needed for proper sizes
                            // calculation, but may be hidden from user.
-    kShortcut = 5          // A link that must not be followed during
+    kShortcut = 5,         // A link that must not be followed during
                            // sizes calculation.
+    kWeak = 6              // A weak reference (ignored by the GC).
   };
 
   /** Returns edge type (see HeapGraphEdge::Type). */

src/bootstrapper.cc

@@ -299,7 +299,7 @@ class Genesis BASE_EMBEDDED {
 
 void Bootstrapper::Iterate(ObjectVisitor* v) {
   extensions_cache_.Iterate(v);
-  v->Synchronize("Extensions");
+  v->Synchronize(VisitorSynchronization::kExtensions);
 }
 
 

src/heap.cc

@@ -5151,29 +5151,29 @@ void Heap::IterateRoots(ObjectVisitor* v, VisitMode mode) {
 
 void Heap::IterateWeakRoots(ObjectVisitor* v, VisitMode mode) {
   v->VisitPointer(reinterpret_cast<Object**>(&roots_[kSymbolTableRootIndex]));
-  v->Synchronize("symbol_table");
+  v->Synchronize(VisitorSynchronization::kSymbolTable);
   if (mode != VISIT_ALL_IN_SCAVENGE &&
       mode != VISIT_ALL_IN_SWEEP_NEWSPACE) {
     // Scavenge collections have special processing for this.
     external_string_table_.Iterate(v);
   }
-  v->Synchronize("external_string_table");
+  v->Synchronize(VisitorSynchronization::kExternalStringsTable);
 }
 
 
 void Heap::IterateStrongRoots(ObjectVisitor* v, VisitMode mode) {
   v->VisitPointers(&roots_[0], &roots_[kStrongRootListLength]);
-  v->Synchronize("strong_root_list");
+  v->Synchronize(VisitorSynchronization::kStrongRootList);
 
   v->VisitPointer(BitCast<Object**>(&hidden_symbol_));
-  v->Synchronize("symbol");
+  v->Synchronize(VisitorSynchronization::kSymbol);
 
   isolate_->bootstrapper()->Iterate(v);
-  v->Synchronize("bootstrapper");
+  v->Synchronize(VisitorSynchronization::kBootstrapper);
   isolate_->Iterate(v);
-  v->Synchronize("top");
+  v->Synchronize(VisitorSynchronization::kTop);
   Relocatable::Iterate(v);
-  v->Synchronize("relocatable");
+  v->Synchronize(VisitorSynchronization::kRelocatable);
 
 #ifdef ENABLE_DEBUGGER_SUPPORT
   isolate_->debug()->Iterate(v);
@@ -5181,13 +5181,13 @@ void Heap::IterateStrongRoots(ObjectVisitor* v, VisitMode mode) {
     isolate_->deoptimizer_data()->Iterate(v);
   }
 #endif
-  v->Synchronize("debug");
+  v->Synchronize(VisitorSynchronization::kDebug);
   isolate_->compilation_cache()->Iterate(v);
-  v->Synchronize("compilationcache");
+  v->Synchronize(VisitorSynchronization::kCompilationCache);
 
   // Iterate over local handles in handle scopes.
   isolate_->handle_scope_implementer()->Iterate(v);
-  v->Synchronize("handlescope");
+  v->Synchronize(VisitorSynchronization::kHandleScope);
 
   // Iterate over the builtin code objects and code stubs in the
   // heap. Note that it is not necessary to iterate over code objects
@@ -5195,7 +5195,7 @@ void Heap::IterateStrongRoots(ObjectVisitor* v, VisitMode mode) {
   if (mode != VISIT_ALL_IN_SCAVENGE) {
     isolate_->builtins()->IterateBuiltins(v);
   }
-  v->Synchronize("builtins");
+  v->Synchronize(VisitorSynchronization::kBuiltins);
 
   // Iterate over global handles.
   switch (mode) {
@@ -5210,11 +5210,11 @@ void Heap::IterateStrongRoots(ObjectVisitor* v, VisitMode mode) {
       isolate_->global_handles()->IterateAllRoots(v);
       break;
   }
-  v->Synchronize("globalhandles");
+  v->Synchronize(VisitorSynchronization::kGlobalHandles);
 
   // Iterate over pointers being held by inactive threads.
   isolate_->thread_manager()->Iterate(v);
-  v->Synchronize("threadmanager");
+  v->Synchronize(VisitorSynchronization::kThreadManager);
 
   // Iterate over the pointers the Serialization/Deserialization code is
   // holding.

src/objects.cc

@@ -7639,6 +7639,22 @@ void SharedFunctionInfo::CompleteInobjectSlackTracking() {
 }
 
 
+#define DECLARE_TAG(ignore1, name, ignore2) name,
+const char* const VisitorSynchronization::kTags[
+    VisitorSynchronization::kNumberOfSyncTags] = {
+  VISITOR_SYNCHRONIZATION_TAGS_LIST(DECLARE_TAG)
+};
+#undef DECLARE_TAG
+
+
+#define DECLARE_TAG(ignore1, ignore2, name) name,
+const char* const VisitorSynchronization::kTagNames[
+    VisitorSynchronization::kNumberOfSyncTags] = {
+  VISITOR_SYNCHRONIZATION_TAGS_LIST(DECLARE_TAG)
+};
+#undef DECLARE_TAG
+
+
 void ObjectVisitor::VisitCodeTarget(RelocInfo* rinfo) {
   ASSERT(RelocInfo::IsCodeTarget(rinfo->rmode()));
   Object* target = Code::GetCodeFromTargetAddress(rinfo->target_address());

src/objects.h

@@ -7862,6 +7862,34 @@ class BreakPointInfo: public Struct {
 #undef DECL_BOOLEAN_ACCESSORS
 #undef DECL_ACCESSORS
 
+#define VISITOR_SYNCHRONIZATION_TAGS_LIST(V)                            \
+  V(kSymbolTable, "symbol_table", "(Symbols)")                          \
+  V(kExternalStringsTable, "external_strings_table", "(External strings)") \
+  V(kStrongRootList, "strong_root_list", "(Strong roots)")              \
+  V(kSymbol, "symbol", "(Symbol)")                                      \
+  V(kBootstrapper, "bootstrapper", "(Bootstrapper)")                    \
+  V(kTop, "top", "(Isolate)")                                           \
+  V(kRelocatable, "relocatable", "(Relocatable)")                       \
+  V(kDebug, "debug", "(Debugger)")                                      \
+  V(kCompilationCache, "compilationcache", "(Compilation cache)")       \
+  V(kHandleScope, "handlescope", "(Handle scope)")                      \
+  V(kBuiltins, "builtins", "(Builtins)")                                \
+  V(kGlobalHandles, "globalhandles", "(Global handles)")                \
+  V(kThreadManager, "threadmanager", "(Thread manager)")                \
+  V(kExtensions, "Extensions", "(Extensions)")
+
+class VisitorSynchronization : public AllStatic {
+ public:
+#define DECLARE_ENUM(enum_item, ignore1, ignore2) enum_item,
+  enum SyncTag {
+    VISITOR_SYNCHRONIZATION_TAGS_LIST(DECLARE_ENUM)
+    kNumberOfSyncTags
+  };
+#undef DECLARE_ENUM
+
+  static const char* const kTags[kNumberOfSyncTags];
+  static const char* const kTagNames[kNumberOfSyncTags];
+};
 
 // Abstract base class for visiting, and optionally modifying, the
 // pointers contained in Objects. Used in GC and serialization/deserialization.
@@ -7917,13 +7945,10 @@ class ObjectVisitor BASE_EMBEDDED {
   // Visits a handle that has an embedder-assigned class ID.
   virtual void VisitEmbedderReference(Object** p, uint16_t class_id) {}
 
-#ifdef DEBUG
   // Intended for serialization/deserialization checking: insert, or
   // check for the presence of, a tag at this position in the stream.
-  virtual void Synchronize(const char* tag) {}
-#else
-  inline void Synchronize(const char* tag) {}
-#endif
+  // Also used for marking up GC roots in heap snapshots.
+  virtual void Synchronize(VisitorSynchronization::SyncTag tag) {}
 };
 
 

src/profile-generator-inl.h

@@ -95,6 +95,25 @@ CodeEntry* ProfileGenerator::EntryForVMState(StateTag tag) {
 }
 
 
+uint64_t HeapObjectsMap::GetNthGcSubrootId(int delta) {
+  return kGcRootsObjectId + delta * kObjectIdStep;
+}
+
+
+HeapObject* V8HeapExplorer::GetNthGcSubrootObject(int delta) {
+  return reinterpret_cast<HeapObject*>(
+      reinterpret_cast<char*>(kFirstGcSubrootObject) +
+      delta * HeapObjectsMap::kObjectIdStep);
+}
+
+
+int V8HeapExplorer::GetGcSubrootOrder(HeapObject* subroot) {
+  return (reinterpret_cast<char*>(subroot) -
+          reinterpret_cast<char*>(kFirstGcSubrootObject)) /
+      HeapObjectsMap::kObjectIdStep;
+}
+
+
 uint64_t HeapEntry::id() {
   union {
     Id stored_id;

src/profile-generator.h

@@ -455,7 +455,8 @@ class HeapGraphEdge BASE_EMBEDDED {
     kProperty = v8::HeapGraphEdge::kProperty,
     kInternal = v8::HeapGraphEdge::kInternal,
     kHidden = v8::HeapGraphEdge::kHidden,
-    kShortcut = v8::HeapGraphEdge::kShortcut
+    kShortcut = v8::HeapGraphEdge::kShortcut,
+    kWeak = v8::HeapGraphEdge::kWeak
   };
 
   HeapGraphEdge() { }
@@ -465,7 +466,7 @@ class HeapGraphEdge BASE_EMBEDDED {
 
   Type type() { return static_cast<Type>(type_); }
   int index() {
-    ASSERT(type_ == kElement || type_ == kHidden);
+    ASSERT(type_ == kElement || type_ == kHidden || type_ == kWeak);
     return index_;
   }
   const char* name() {
@@ -588,7 +589,8 @@ class HeapEntry BASE_EMBEDDED {
   int EntrySize() { return EntriesSize(1, children_count_, retainers_count_); }
   int RetainedSize(bool exact);
 
-  void Print(int max_depth, int indent);
+  void Print(
+      const char* prefix, const char* edge_name, int max_depth, int indent);
 
   Handle<HeapObject> GetHeapObject();
 
@@ -661,6 +663,7 @@ class HeapSnapshot {
   HeapEntry* root() { return root_entry_; }
   HeapEntry* gc_roots() { return gc_roots_entry_; }
   HeapEntry* natives_root() { return natives_root_entry_; }
+  HeapEntry* gc_subroot(int index) { return gc_subroot_entries_[index]; }
   List<HeapEntry*>* entries() { return &entries_; }
   int raw_entries_size() { return raw_entries_size_; }
 
@@ -674,6 +677,9 @@ class HeapSnapshot {
                       int retainers_count);
   HeapEntry* AddRootEntry(int children_count);
   HeapEntry* AddGcRootsEntry(int children_count, int retainers_count);
+  HeapEntry* AddGcSubrootEntry(int tag,
+                               int children_count,
+                               int retainers_count);
   HeapEntry* AddNativesRootEntry(int children_count, int retainers_count);
   void ClearPaint();
   HeapEntry* GetEntryById(uint64_t id);
@@ -695,6 +701,7 @@ class HeapSnapshot {
   HeapEntry* root_entry_;
   HeapEntry* gc_roots_entry_;
   HeapEntry* natives_root_entry_;
+  HeapEntry* gc_subroot_entries_[VisitorSynchronization::kNumberOfSyncTags];
   char* raw_entries_;
   List<HeapEntry*> entries_;
   bool entries_sorted_;
@@ -716,10 +723,13 @@ class HeapObjectsMap {
   void MoveObject(Address from, Address to);
 
   static uint64_t GenerateId(v8::RetainedObjectInfo* info);
+  static inline uint64_t GetNthGcSubrootId(int delta);
 
+  static const int kObjectIdStep = 2;
   static const uint64_t kInternalRootObjectId;
   static const uint64_t kGcRootsObjectId;
   static const uint64_t kNativesRootObjectId;
+  static const uint64_t kGcRootsFirstSubrootId;
   static const uint64_t kFirstAvailableObjectId;
 
  private:
@@ -969,6 +979,11 @@ class V8HeapExplorer : public HeapEntriesAllocator {
                           HeapEntry* parent,
                           int index,
                           Object* child);
+  void SetWeakReference(HeapObject* parent_obj,
+                        HeapEntry* parent_entry,
+                        int index,
+                        Object* child_obj,
+                        int field_offset);
   void SetPropertyReference(HeapObject* parent_obj,
                             HeapEntry* parent,
                             String* reference_name,
@@ -981,11 +996,16 @@ class V8HeapExplorer : public HeapEntriesAllocator {
                                     Object* child);
   void SetRootShortcutReference(Object* child);
   void SetRootGcRootsReference();
-  void SetGcRootsReference(Object* child);
+  void SetGcRootsReference(VisitorSynchronization::SyncTag tag);
+  void SetGcSubrootReference(
+      VisitorSynchronization::SyncTag tag, bool is_weak, Object* child);
   void TagObject(Object* obj, const char* tag);
 
   HeapEntry* GetEntry(Object* obj);
 
+  static inline HeapObject* GetNthGcSubrootObject(int delta);
+  static inline int GetGcSubrootOrder(HeapObject* subroot);
+
   Heap* heap_;
   HeapSnapshot* snapshot_;
   HeapSnapshotsCollection* collection_;
@@ -994,8 +1014,11 @@ class V8HeapExplorer : public HeapEntriesAllocator {
   HeapObjectsSet objects_tags_;
 
   static HeapObject* const kGcRootsObject;
+  static HeapObject* const kFirstGcSubrootObject;
+  static HeapObject* const kLastGcSubrootObject;
 
   friend class IndexedReferencesExtractor;
+  friend class GcSubrootsEnumerator;
   friend class RootsReferencesExtractor;
 
   DISALLOW_COPY_AND_ASSIGN(V8HeapExplorer);

test/cctest/test-heap-profiler.cc

@@ -1065,3 +1065,82 @@ TEST(FastCaseGetter) {
       GetProperty(obj1, v8::HeapGraphEdge::kProperty, "set-propWithSetter");
   CHECK_NE(NULL, setterFunction);
 }
+
+
+bool HasWeakEdge(const v8::HeapGraphNode* node) {
+  for (int i = 0; i < node->GetChildrenCount(); ++i) {
+    const v8::HeapGraphEdge* handle_edge = node->GetChild(i);
+    if (handle_edge->GetType() == v8::HeapGraphEdge::kWeak) return true;
+  }
+  return false;
+}
+
+
+bool HasWeakGlobalHandle() {
+  const v8::HeapSnapshot* snapshot =
+      v8::HeapProfiler::TakeSnapshot(v8_str("weaks"));
+  const v8::HeapGraphNode* gc_roots = GetNode(
+      snapshot->GetRoot(), v8::HeapGraphNode::kObject, "(GC roots)");
+  CHECK_NE(NULL, gc_roots);
+  const v8::HeapGraphNode* global_handles = GetNode(
+      gc_roots, v8::HeapGraphNode::kObject, "(Global handles)");
+  CHECK_NE(NULL, global_handles);
+  return HasWeakEdge(global_handles);
+}
+
+
+static void PersistentHandleCallback(v8::Persistent<v8::Value> handle, void*) {
+  handle.Dispose();
+}
+
+
+TEST(WeakGlobalHandle) {
+  v8::HandleScope scope;
+  LocalContext env;
+
+  CHECK(!HasWeakGlobalHandle());
+
+  v8::Persistent<v8::Object> handle =
+      v8::Persistent<v8::Object>::New(v8::Object::New());
+  handle.MakeWeak(NULL, PersistentHandleCallback);
+
+  CHECK(HasWeakGlobalHandle());
+}
+
+
+TEST(WeakGlobalContextRefs) {
+  v8::HandleScope scope;
+  LocalContext env;
+
+  const v8::HeapSnapshot* snapshot =
+      v8::HeapProfiler::TakeSnapshot(v8_str("weaks"));
+  const v8::HeapGraphNode* gc_roots = GetNode(
+      snapshot->GetRoot(), v8::HeapGraphNode::kObject, "(GC roots)");
+  CHECK_NE(NULL, gc_roots);
+  const v8::HeapGraphNode* global_handles = GetNode(
+      gc_roots, v8::HeapGraphNode::kObject, "(Global handles)");
+  CHECK_NE(NULL, global_handles);
+  const v8::HeapGraphNode* global_context = GetNode(
+      global_handles, v8::HeapGraphNode::kHidden, "system / GlobalContext");
+  CHECK_NE(NULL, global_context);
+  CHECK(HasWeakEdge(global_context));
+}
+
+
+TEST(SfiAndJsFunctionWeakRefs) {
+  v8::HandleScope scope;
+  LocalContext env;
+
+  CompileRun(
+      "fun = (function (x) { return function () { return x + 1; } })(1);");
+  const v8::HeapSnapshot* snapshot =
+      v8::HeapProfiler::TakeSnapshot(v8_str("fun"));
+  const v8::HeapGraphNode* global = GetGlobalObject(snapshot);
+  CHECK_NE(NULL, global);
+  const v8::HeapGraphNode* fun =
+      GetProperty(global, v8::HeapGraphEdge::kShortcut, "fun");
+  CHECK(HasWeakEdge(fun));
+  const v8::HeapGraphNode* shared =
+      GetProperty(fun, v8::HeapGraphEdge::kInternal, "shared");
+  CHECK(HasWeakEdge(shared));
+}