Use a walking visitor to traverse JSObject structure.

src/objects.cc

 // Copyright 2013 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 5565 matching lines @@
 }
 
 
 Handle<JSObject> JSObject::Copy(Handle<JSObject> object) {
   Isolate* isolate = object->GetIsolate();
   CALL_HEAP_FUNCTION(isolate,
                      isolate->heap()->CopyJSObject(*object), JSObject);
 }
 
 
-Handle<JSObject> JSObject::DeepCopy(Handle<JSObject> object) {
+class JSObjectWalkVisitor {
+ public:
+  explicit JSObjectWalkVisitor() {}
+  virtual ~JSObjectWalkVisitor() {}
+
+  Handle<JSObject> Visit(Handle<JSObject> object) {
+    return StructureWalk(object, this);
+  }
+
+  // Returns true if the visitor is a copying visitor.
+  virtual bool is_copying() = 0;
+
+ protected:
+  Handle<JSObject> StructureWalk(Handle<JSObject> object,
+                                 JSObjectWalkVisitor* visitor);
+
+  // The returned handle should point to a new object if the visitor is a
+  // copying visitor, otherwise it should be the same as the input object.
+  virtual Handle<JSObject> VisitObject(Handle<JSObject> object) = 0;
+
+  // The returned handle should point to a new value if the visitor is a
+  // copying visitor, otherwise it should be the same as the input value.
+  virtual Handle<JSObject> VisitElementOrProperty(Handle<JSObject> object,
+                                                  Handle<JSObject> value) = 0;
+};
+
+
+class JSObjectCopyVisitor: public JSObjectWalkVisitor {
+ public:
+  explicit JSObjectCopyVisitor() {}
+
+  virtual bool is_copying() V8_OVERRIDE { return true; }
+
+ protected:
+  virtual Handle<JSObject> VisitObject(Handle<JSObject> object) V8_OVERRIDE {
+    return JSObject::Copy(object);
+  }
+
+  virtual Handle<JSObject> VisitElementOrProperty(
+      Handle<JSObject> object,
+      Handle<JSObject> value) V8_OVERRIDE {
+    return StructureWalk(value, this);

[Yang, 2013/09/30 09:37:25]

Why do you need to pass 'this' explicitly? The copy visitor class inherits (the
non-static) StructureWalk, wouldn't it pass itself implicitly as receiver
anyways?

[mvstanton, 2013/09/30 11:35:51]

thx for that, first StructureWalk was a static function, not a memeber of the
class, this is a leftover artifact. Fixed!

+  }
+};
+
+
+Handle<JSObject> JSObjectWalkVisitor::StructureWalk(
+    Handle<JSObject> object,
+    JSObjectWalkVisitor* visitor) {
+  bool is_copying = visitor->is_copying();
   Isolate* isolate = object->GetIsolate();
   StackLimitCheck check(isolate);
   if (check.HasOverflowed()) {
     isolate->StackOverflow();
     return Handle<JSObject>::null();
   }
 
   if (object->map()->is_deprecated()) {
-    MigrateInstance(object);
+    JSObject::MigrateInstance(object);
   }
 
-  Handle<JSObject> copy = Copy(object);
+  Handle<JSObject> copy = visitor->VisitObject(object);
+  ASSERT(visitor->is_copying() || copy.is_identical_to(object));
 
   HandleScope scope(isolate);
 
   // Deep copy local properties.
   if (copy->HasFastProperties()) {
     Handle<DescriptorArray> descriptors(copy->map()->instance_descriptors());
     int limit = copy->map()->NumberOfOwnDescriptors();
     for (int i = 0; i < limit; i++) {
       PropertyDetails details = descriptors->GetDetails(i);
       if (details.type() != FIELD) continue;
       int index = descriptors->GetFieldIndex(i);
       Handle<Object> value(object->RawFastPropertyAt(index), isolate);
       if (value->IsJSObject()) {
-        value = DeepCopy(Handle<JSObject>::cast(value));
+        value = visitor->VisitElementOrProperty(copy,
+                                                Handle<JSObject>::cast(value));
         RETURN_IF_EMPTY_HANDLE_VALUE(isolate, value, Handle<JSObject>());
       } else {
         Representation representation = details.representation();
         value = NewStorageFor(isolate, value, representation);
       }
-      copy->FastPropertyAtPut(index, *value);
+      if (is_copying) {
+        copy->FastPropertyAtPut(index, *value);
+      }
     }
   } else {
     Handle<FixedArray> names =
         isolate->factory()->NewFixedArray(copy->NumberOfLocalProperties());
     copy->GetLocalPropertyNames(*names, 0);
     for (int i = 0; i < names->length(); i++) {
       ASSERT(names->get(i)->IsString());
       Handle<String> key_string(String::cast(names->get(i)));
       PropertyAttributes attributes =
           copy->GetLocalPropertyAttribute(*key_string);
       // Only deep copy fields from the object literal expression.
       // In particular, don't try to copy the length attribute of
       // an array.
       if (attributes != NONE) continue;
       Handle<Object> value(
           copy->GetProperty(*key_string, &attributes)->ToObjectUnchecked(),
           isolate);
       if (value->IsJSObject()) {
-        Handle<Object> result = DeepCopy(Handle<JSObject>::cast(value));
+        Handle<JSObject> result = visitor->VisitElementOrProperty(
+            copy, Handle<JSObject>::cast(value));
         RETURN_IF_EMPTY_HANDLE_VALUE(isolate, result, Handle<JSObject>());
-        // Creating object copy for literals. No strict mode needed.
-        CHECK_NOT_EMPTY_HANDLE(isolate, SetProperty(
-            copy, key_string, result, NONE, kNonStrictMode));
+        if (is_copying) {
+          // Creating object copy for literals. No strict mode needed.
+          CHECK_NOT_EMPTY_HANDLE(isolate, JSObject::SetProperty(
+              copy, key_string, result, NONE, kNonStrictMode));
+        }
       }
     }
   }
 
   // Deep copy local elements.
   // Pixel elements cannot be created using an object literal.
   ASSERT(!copy->HasExternalArrayElements());
   switch (copy->GetElementsKind()) {
     case FAST_SMI_ELEMENTS:
     case FAST_ELEMENTS:
     case FAST_HOLEY_SMI_ELEMENTS:
     case FAST_HOLEY_ELEMENTS: {
       Handle<FixedArray> elements(FixedArray::cast(copy->elements()));
       if (elements->map() == isolate->heap()->fixed_cow_array_map()) {
         isolate->counters()->cow_arrays_created_runtime()->Increment();
 #ifdef DEBUG
         for (int i = 0; i < elements->length(); i++) {
           ASSERT(!elements->get(i)->IsJSObject());
         }
 #endif
       } else {
         for (int i = 0; i < elements->length(); i++) {
           Handle<Object> value(elements->get(i), isolate);
           ASSERT(value->IsSmi() ||
                  value->IsTheHole() ||
                  (IsFastObjectElementsKind(copy->GetElementsKind())));
           if (value->IsJSObject()) {
-            Handle<Object> result = DeepCopy(Handle<JSObject>::cast(value));
+            Handle<JSObject> result = visitor->VisitElementOrProperty(
+                copy, Handle<JSObject>::cast(value));
             RETURN_IF_EMPTY_HANDLE_VALUE(isolate, result, Handle<JSObject>());
-            elements->set(i, *result);
+            if (is_copying) {
+              elements->set(i, *result);
+            }
           }
         }
       }
       break;
     }
     case DICTIONARY_ELEMENTS: {
       Handle<SeededNumberDictionary> element_dictionary(
           copy->element_dictionary());
       int capacity = element_dictionary->Capacity();
       for (int i = 0; i < capacity; i++) {
         Object* k = element_dictionary->KeyAt(i);
         if (element_dictionary->IsKey(k)) {
           Handle<Object> value(element_dictionary->ValueAt(i), isolate);
           if (value->IsJSObject()) {
-            Handle<Object> result = DeepCopy(Handle<JSObject>::cast(value));
+            Handle<JSObject> result = visitor->VisitElementOrProperty(
+                copy, Handle<JSObject>::cast(value));
             RETURN_IF_EMPTY_HANDLE_VALUE(isolate, result, Handle<JSObject>());
-            element_dictionary->ValueAtPut(i, *result);
+            if (is_copying) {
+              element_dictionary->ValueAtPut(i, *result);
+            }
           }
         }
       }
       break;
     }
     case NON_STRICT_ARGUMENTS_ELEMENTS:
       UNIMPLEMENTED();
       break;
     case EXTERNAL_PIXEL_ELEMENTS:
     case EXTERNAL_BYTE_ELEMENTS:
     case EXTERNAL_UNSIGNED_BYTE_ELEMENTS:
     case EXTERNAL_SHORT_ELEMENTS:
     case EXTERNAL_UNSIGNED_SHORT_ELEMENTS:
     case EXTERNAL_INT_ELEMENTS:
     case EXTERNAL_UNSIGNED_INT_ELEMENTS:
     case EXTERNAL_FLOAT_ELEMENTS:
     case EXTERNAL_DOUBLE_ELEMENTS:
     case FAST_DOUBLE_ELEMENTS:
     case FAST_HOLEY_DOUBLE_ELEMENTS:
       // No contained objects, nothing to do.
       break;
   }
   return copy;
 }
 
 
+Handle<JSObject> JSObject::DeepCopy(Handle<JSObject> object) {
+  JSObjectCopyVisitor v;
+  Handle<JSObject> copy = v.Visit(object);
+  ASSERT(v.is_copying() && !copy.is_identical_to(object));
+  return copy;
+}
+
+
 // Tests for the fast common case for property enumeration:
 // - This object and all prototypes has an enum cache (which means that
 //   it is no proxy, has no interceptors and needs no access checks).
 // - This object has no elements.
 // - No prototype has enumerable properties/elements.
 bool JSReceiver::IsSimpleEnum() {
   Heap* heap = GetHeap();
   for (Object* o = this;
        o != heap->null_value();
        o = JSObject::cast(o)->GetPrototype()) {
@@ skipping 10394 matching lines @@
 #define ERROR_MESSAGES_TEXTS(C, T) T,
   static const char* error_messages_[] = {
       ERROR_MESSAGES_LIST(ERROR_MESSAGES_TEXTS)
   };
 #undef ERROR_MESSAGES_TEXTS
   return error_messages_[reason];
 }
 
 
 } }  // namespace v8::internal