Introduce object visitor to estimate the size of a native context.

src/context-measure.cc

+// Copyright 2015 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/v8.h"
+
+#include "src/context-measure.h"
+
+namespace v8 {
+namespace internal {
+
+ContextMeasure::ContextMeasure(Context* context)
+    : context_(context),
+      root_index_map_(context->GetIsolate()),
+      recursion_depth_(0),
+      count_(0),
+      size_(0) {
+  DCHECK(context_->IsNativeContext());
+  Object* next_link = context_->get(Context::NEXT_CONTEXT_LINK);
+  MeasureObject(context_);
+  MeasureDeferredObjects();
+  context_->set(Context::NEXT_CONTEXT_LINK, next_link);
+}
+
+
+bool ContextMeasure::IsShared(HeapObject* object) {
+  if (object->IsScript()) return true;
+  if (object->IsSharedFunctionInfo()) return true;
+  if (object->IsScopeInfo()) return true;
+  if (object->IsCode() && !Code::cast(object)->is_optimized_code()) return true;
+  if (object->IsExecutableAccessorInfo()) return true;
+  if (object->IsWeakCell()) return true;
+  return false;
+}
+
+
+void ContextMeasure::MeasureObject(HeapObject* object) {
+  if (back_reference_map_.Lookup(object).is_valid()) return;
+  if (root_index_map_.Lookup(object) != RootIndexMap::kInvalidRootIndex) return;
+  if (IsShared(object)) return;
+  back_reference_map_.Add(object, BackReference::DummyReference());
+  recursion_depth_++;
+  if (recursion_depth_ > kMaxRecursion) {
+    deferred_objects_.Add(object);
+  } else {
+    MeasureAndRecurse(object);
+  }
+  recursion_depth_--;
+}
+
+
+void ContextMeasure::MeasureDeferredObjects() {
+  while (deferred_objects_.length() > 0) {
+    MeasureAndRecurse(deferred_objects_.RemoveLast());
+  }
+}
+
+
+void ContextMeasure::MeasureAndRecurse(HeapObject* object) {
+  int size = object->Size();
+  count_++;
+  size_ += size;
+  Map* map = object->map();
+  MeasureObject(map);
+  object->IterateBody(map->instance_type(), size, this);
+}
+
+
+void ContextMeasure::VisitPointers(Object** start, Object** end) {
+  for (Object** current = start; current < end; current++) {
+    if ((*current)->IsSmi()) continue;
+    MeasureObject(HeapObject::cast(*current));
+  }
+}
+}
+}  // namespace v8::internal