Don't intrusively mark in the heap snapshot generator

src/profiler/heap-snapshot-generator.cc

 // Copyright 2013 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/profiler/heap-snapshot-generator.h"
 
 #include "src/code-stubs.h"
 #include "src/conversions.h"
 #include "src/debug/debug.h"
 #include "src/objects-body-descriptors.h"
@@ skipping 970 matching lines @@
        obj != NULL;
        obj = iterator->next()) {
     objects_count++;
   }
   return objects_count;
 }
 
 
 class IndexedReferencesExtractor : public ObjectVisitor {
  public:
-  IndexedReferencesExtractor(V8HeapExplorer* generator,
-                             HeapObject* parent_obj,
+  IndexedReferencesExtractor(V8HeapExplorer* generator, HeapObject* parent_obj,
                              int parent)
       : generator_(generator),
         parent_obj_(parent_obj),
+        real_end_(HeapObject::RawField(parent_obj_, parent_obj_->Size())),
         parent_(parent),
-        next_index_(0) {
-  }
+        next_index_(0) {}
   void VisitCodeEntry(Address entry_address) override {
      Code* code = Code::cast(Code::GetObjectFromEntryAddress(entry_address));
      generator_->SetInternalReference(parent_obj_, parent_, "code", code);
      generator_->TagCodeObject(code);
   }
   void VisitPointers(Object** start, Object** end) override {
     for (Object** p = start; p < end; p++) {
+      intptr_t index =
+          static_cast<intptr_t>(p - HeapObject::RawField(parent_obj_, 0));
       ++next_index_;
-      if (CheckVisitedAndUnmark(p)) continue;
+      if (p >= HeapObject::RawField(parent_obj_, 0) && p < real_end_ &&

[Igor Sheludko, 2015/11/27 10:16:39]

I think it would be cleaner to have both object_start_ and object_end_ fields.

And please add a comment why do we need the range checking.

+          generator_->marks_[index]) {
+        generator_->marks_[index] = false;
+        continue;
+      }
       generator_->SetHiddenReference(parent_obj_, parent_, next_index_, *p);
     }
   }
-  static void MarkVisitedField(HeapObject* obj, int offset) {
-    if (offset < 0) return;
-    Address field = obj->address() + offset;
-    DCHECK(Memory::Object_at(field)->IsHeapObject());
-    intptr_t p = reinterpret_cast<intptr_t>(Memory::Object_at(field));
-    DCHECK(!IsMarked(p));
-    intptr_t p_tagged = p | kTag;
-    Memory::Object_at(field) = reinterpret_cast<Object*>(p_tagged);
-  }
 
  private:
-  bool CheckVisitedAndUnmark(Object** field) {
-    intptr_t p = reinterpret_cast<intptr_t>(*field);
-    if (IsMarked(p)) {
-      intptr_t p_untagged = (p & ~kTaggingMask) | kHeapObjectTag;
-      *field = reinterpret_cast<Object*>(p_untagged);
-      DCHECK((*field)->IsHeapObject());
-      return true;
-    }
-    return false;
-  }
-
-  static const intptr_t kTaggingMask = 3;
-  static const intptr_t kTag = 3;
-
-  static bool IsMarked(intptr_t p) { return (p & kTaggingMask) == kTag; }
-
   V8HeapExplorer* generator_;
   HeapObject* parent_obj_;
+  Object** real_end_;
   int parent_;
   int next_index_;
 };
 
 
 bool V8HeapExplorer::ExtractReferencesPass1(int entry, HeapObject* obj) {
   if (obj->IsFixedArray()) return false;  // FixedArrays are processed on pass 2
 
   if (obj->IsJSGlobalProxy()) {
     ExtractJSGlobalProxyReferences(entry, JSGlobalProxy::cast(obj));
@@ skipping 814 matching lines @@
 bool V8HeapExplorer::IterateAndExtractSinglePass() {
   // Now iterate the whole heap.
   bool interrupted = false;
   HeapIterator iterator(heap_, HeapIterator::kFilterUnreachable);
   // Heap iteration with filtering must be finished in any case.
   for (HeapObject* obj = iterator.next();
        obj != NULL;
        obj = iterator.next(), progress_->ProgressStep()) {
     if (interrupted) continue;
 
+    int max_pointer = obj->Size() / kPointerSize;
+    if (max_pointer > marks_.size()) {
+      // Clear the current bits.
+      std::vector<bool>().swap(marks_);
+      // Reallocate to right size.
+      marks_.resize(max_pointer, false);
+    }
+
     HeapEntry* heap_entry = GetEntry(obj);
     int entry = heap_entry->index();
     if ((this->*extractor)(entry, obj)) {
       SetInternalReference(obj, entry,
                            "map", obj->map(), HeapObject::kMapOffset);
       // Extract unvisited fields as hidden references and restore tags
       // of visited fields.
       IndexedReferencesExtractor refs_extractor(this, obj, entry);
       obj->Iterate(&refs_extractor);
     }
@@ skipping 24 matching lines @@
                                          String* reference_name,
                                          Object* child_obj,
                                          int field_offset) {
   DCHECK(parent_entry == GetEntry(parent_obj)->index());
   HeapEntry* child_entry = GetEntry(child_obj);
   if (child_entry != NULL) {
     filler_->SetNamedReference(HeapGraphEdge::kContextVariable,
                                parent_entry,
                                names_->GetName(reference_name),
                                child_entry);
-    IndexedReferencesExtractor::MarkVisitedField(parent_obj, field_offset);
+    MarkVisitedField(parent_obj, field_offset);
   }
 }
 
 
+void V8HeapExplorer::MarkVisitedField(HeapObject* obj, int offset) {
+  if (offset < 0) return;
+  int index = offset / kPointerSize;
+  DCHECK(!marks_[index]);
+  marks_[index] = true;
+}
+
+
 void V8HeapExplorer::SetNativeBindReference(HeapObject* parent_obj,
                                             int parent_entry,
                                             const char* reference_name,
                                             Object* child_obj) {
   DCHECK(parent_entry == GetEntry(parent_obj)->index());
   HeapEntry* child_entry = GetEntry(child_obj);
   if (child_entry != NULL) {
     filler_->SetNamedReference(HeapGraphEdge::kShortcut,
                                parent_entry,
                                reference_name,
@@ skipping 24 matching lines @@
                                           int field_offset) {
   DCHECK(parent_entry == GetEntry(parent_obj)->index());
   HeapEntry* child_entry = GetEntry(child_obj);
   if (child_entry == NULL) return;
   if (IsEssentialObject(child_obj)) {
     filler_->SetNamedReference(HeapGraphEdge::kInternal,
                                parent_entry,
                                reference_name,
                                child_entry);
   }
-  IndexedReferencesExtractor::MarkVisitedField(parent_obj, field_offset);
+  MarkVisitedField(parent_obj, field_offset);
 }
 
 
 void V8HeapExplorer::SetInternalReference(HeapObject* parent_obj,
                                           int parent_entry,
                                           int index,
                                           Object* child_obj,
                                           int field_offset) {
   DCHECK(parent_entry == GetEntry(parent_obj)->index());
   HeapEntry* child_entry = GetEntry(child_obj);
   if (child_entry == NULL) return;
   if (IsEssentialObject(child_obj)) {
     filler_->SetNamedReference(HeapGraphEdge::kInternal,
                                parent_entry,
                                names_->GetName(index),
                                child_entry);
   }
-  IndexedReferencesExtractor::MarkVisitedField(parent_obj, field_offset);
+  MarkVisitedField(parent_obj, field_offset);
 }
 
 
 void V8HeapExplorer::SetHiddenReference(HeapObject* parent_obj,
                                         int parent_entry,
                                         int index,
                                         Object* child_obj) {
   DCHECK(parent_entry == GetEntry(parent_obj)->index());
   HeapEntry* child_entry = GetEntry(child_obj);
   if (child_entry != NULL && IsEssentialObject(child_obj)) {
@@ skipping 12 matching lines @@
                                       int field_offset) {
   DCHECK(parent_entry == GetEntry(parent_obj)->index());
   HeapEntry* child_entry = GetEntry(child_obj);
   if (child_entry == NULL) return;
   if (IsEssentialObject(child_obj)) {
     filler_->SetNamedReference(HeapGraphEdge::kWeak,
                                parent_entry,
                                reference_name,
                                child_entry);
   }
-  IndexedReferencesExtractor::MarkVisitedField(parent_obj, field_offset);
+  MarkVisitedField(parent_obj, field_offset);
 }
 
 
 void V8HeapExplorer::SetWeakReference(HeapObject* parent_obj,
                                       int parent_entry,
                                       int index,
                                       Object* child_obj,
                                       int field_offset) {
   DCHECK(parent_entry == GetEntry(parent_obj)->index());
   HeapEntry* child_entry = GetEntry(child_obj);
   if (child_entry == NULL) return;
   if (IsEssentialObject(child_obj)) {
     filler_->SetNamedReference(HeapGraphEdge::kWeak,
                                parent_entry,
                                names_->GetFormatted("%d", index),
                                child_entry);
   }
-  IndexedReferencesExtractor::MarkVisitedField(parent_obj, field_offset);
+  MarkVisitedField(parent_obj, field_offset);
 }
 
 
 void V8HeapExplorer::SetDataOrAccessorPropertyReference(
     PropertyKind kind, JSObject* parent_obj, int parent_entry,
     Name* reference_name, Object* child_obj, const char* name_format_string,
     int field_offset) {
   if (kind == kAccessor) {
     ExtractAccessorPairProperty(parent_obj, parent_entry, reference_name,
                                 child_obj, field_offset);
@@ skipping 20 matching lines @@
         ? names_->GetFormatted(
               name_format_string,
               String::cast(reference_name)->ToCString(
                   DISALLOW_NULLS, ROBUST_STRING_TRAVERSAL).get()) :
         names_->GetName(reference_name);
 
     filler_->SetNamedReference(type,
                                parent_entry,
                                name,
                                child_entry);
-    IndexedReferencesExtractor::MarkVisitedField(parent_obj, field_offset);
+    MarkVisitedField(parent_obj, field_offset);
   }
 }
 
 
 void V8HeapExplorer::SetRootGcRootsReference() {
   filler_->SetIndexedAutoIndexReference(
       HeapGraphEdge::kElement,
       snapshot_->root()->index(),
       snapshot_->gc_roots());
 }
@@ skipping 1083 matching lines @@
   for (int i = 1; i < sorted_strings.length(); ++i) {
     writer_->AddCharacter(',');
     SerializeString(sorted_strings[i]);
     if (writer_->aborted()) return;
   }
 }
 
 
 }  // namespace internal
 }  // namespace v8