Merge 6800:7180 from the bleeding edge branch to the experimental/gc branch.

src/liveobjectlist.cc

 // Copyright 2011 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 19 matching lines @@
 #include <ctype.h>
 #include <stdlib.h>
 
 #include "v8.h"
 
 #include "checks.h"
 #include "global-handles.h"
 #include "heap.h"
 #include "inspector.h"
 #include "list-inl.h"
-#include "liveobjectlist.h"
+#include "liveobjectlist-inl.h"
 #include "string-stream.h"
 #include "top.h"
 #include "v8utils.h"
 
 namespace v8 {
 namespace internal {
 
 
+typedef int (*RawComparer)(const void*, const void*);
+
+
+#ifdef CHECK_ALL_OBJECT_TYPES
+
+#define DEBUG_LIVE_OBJECT_TYPES(v) \
+  v(Smi, "unexpected: Smi") \
+  \
+  v(CodeCache, "unexpected: CodeCache") \
+  v(BreakPointInfo, "unexpected: BreakPointInfo") \
+  v(DebugInfo, "unexpected: DebugInfo") \
+  v(TypeSwitchInfo, "unexpected: TypeSwitchInfo") \
+  v(SignatureInfo, "unexpected: SignatureInfo") \
+  v(Script, "unexpected: Script") \
+  v(ObjectTemplateInfo, "unexpected: ObjectTemplateInfo") \
+  v(FunctionTemplateInfo, "unexpected: FunctionTemplateInfo") \
+  v(CallHandlerInfo, "unexpected: CallHandlerInfo") \
+  v(InterceptorInfo, "unexpected: InterceptorInfo") \
+  v(AccessCheckInfo, "unexpected: AccessCheckInfo") \
+  v(AccessorInfo, "unexpected: AccessorInfo") \
+  v(ExternalTwoByteString, "unexpected: ExternalTwoByteString") \
+  v(ExternalAsciiString, "unexpected: ExternalAsciiString") \
+  v(ExternalString, "unexpected: ExternalString") \
+  v(SeqTwoByteString, "unexpected: SeqTwoByteString") \
+  v(SeqAsciiString, "unexpected: SeqAsciiString") \
+  v(SeqString, "unexpected: SeqString") \
+  v(JSFunctionResultCache, "unexpected: JSFunctionResultCache") \
+  v(GlobalContext, "unexpected: GlobalContext") \
+  v(MapCache, "unexpected: MapCache") \
+  v(CodeCacheHashTable, "unexpected: CodeCacheHashTable") \
+  v(CompilationCacheTable, "unexpected: CompilationCacheTable") \
+  v(SymbolTable, "unexpected: SymbolTable") \
+  v(Dictionary, "unexpected: Dictionary") \
+  v(HashTable, "unexpected: HashTable") \
+  v(DescriptorArray, "unexpected: DescriptorArray") \
+  v(ExternalFloatArray, "unexpected: ExternalFloatArray") \
+  v(ExternalUnsignedIntArray, "unexpected: ExternalUnsignedIntArray") \
+  v(ExternalIntArray, "unexpected: ExternalIntArray") \
+  v(ExternalUnsignedShortArray, "unexpected: ExternalUnsignedShortArray") \
+  v(ExternalShortArray, "unexpected: ExternalShortArray") \
+  v(ExternalUnsignedByteArray, "unexpected: ExternalUnsignedByteArray") \
+  v(ExternalByteArray, "unexpected: ExternalByteArray") \
+  v(JSValue, "unexpected: JSValue")
+
+#else
+#define DEBUG_LIVE_OBJECT_TYPES(v)
+#endif
+
+
+#define FOR_EACH_LIVE_OBJECT_TYPE(v) \
+  DEBUG_LIVE_OBJECT_TYPES(v) \
+  \
+  v(JSArray, "JSArray") \
+  v(JSRegExp, "JSRegExp") \
+  v(JSFunction, "JSFunction") \
+  v(JSGlobalObject, "JSGlobal") \
+  v(JSBuiltinsObject, "JSBuiltins") \
+  v(GlobalObject, "Global") \
+  v(JSGlobalProxy, "JSGlobalProxy") \
+  v(JSObject, "JSObject") \
+  \
+  v(Context, "meta: Context") \
+  v(ByteArray, "meta: ByteArray") \
+  v(PixelArray, "meta: PixelArray") \
+  v(ExternalArray, "meta: ExternalArray") \
+  v(FixedArray, "meta: FixedArray") \
+  v(String, "String") \
+  v(HeapNumber, "HeapNumber") \
+  \
+  v(Code, "meta: Code") \
+  v(Map, "meta: Map") \
+  v(Oddball, "Oddball") \
+  v(Proxy, "meta: Proxy") \
+  v(SharedFunctionInfo, "meta: SharedFunctionInfo") \
+  v(Struct, "meta: Struct") \
+  \
+  v(HeapObject, "HeapObject")
+
+
+enum /* LiveObjectType */ {
+#define DECLARE_OBJECT_TYPE_ENUM(type, name) kType##type,
+  FOR_EACH_LIVE_OBJECT_TYPE(DECLARE_OBJECT_TYPE_ENUM)
+  kInvalidLiveObjType,
+  kNumberOfTypes
+#undef DECLARE_OBJECT_TYPE_ENUM
+};
+
+
+LiveObjectType GetObjectType(HeapObject* heap_obj) {
+  // TODO(mlam): investigate usint Map::instance_type() instead.
+#define CHECK_FOR_OBJECT_TYPE(type, name) \
+  if (heap_obj->Is##type()) return kType##type;
+  FOR_EACH_LIVE_OBJECT_TYPE(CHECK_FOR_OBJECT_TYPE)
+#undef CHECK_FOR_OBJECT_TYPE
+
+  UNREACHABLE();
+  return kInvalidLiveObjType;
+}
+
+
+inline const char* GetObjectTypeDesc(LiveObjectType type) {
+  static const char* const name[kNumberOfTypes] = {
+  #define DEFINE_OBJECT_TYPE_NAME(type, name) name,
+    FOR_EACH_LIVE_OBJECT_TYPE(DEFINE_OBJECT_TYPE_NAME)
+    "invalid"
+  #undef DEFINE_OBJECT_TYPE_NAME
+  };
+  ASSERT(type < kNumberOfTypes);
+  return name[type];
+}
+
+
+const char* GetObjectTypeDesc(HeapObject* heap_obj) {
+  LiveObjectType type = GetObjectType(heap_obj);
+  return GetObjectTypeDesc(type);
+}
+
+
+bool IsOfType(LiveObjectType type, HeapObject *obj) {
+  // Note: there are types that are more general (e.g. JSObject) that would
+  // have passed the Is##type_() test for more specialized types (e.g.
+  // JSFunction).  If we find a more specialized match but we're looking for
+  // the general type, then we should reject the ones that matches the
+  // specialized type.
+#define CHECK_OBJECT_TYPE(type_, name) \
+  if (obj->Is##type_()) return (type == kType##type_);
+
+  FOR_EACH_LIVE_OBJECT_TYPE(CHECK_OBJECT_TYPE)
+#undef CHECK_OBJECT_TYPE
+
+  return false;
+}
+
+
+const AllocationSpace kInvalidSpace = static_cast<AllocationSpace>(-1);
+
+static AllocationSpace FindSpaceFor(String* space_str) {
+  SmartPointer<char> s =
+      space_str->ToCString(DISALLOW_NULLS, ROBUST_STRING_TRAVERSAL);
+
+  const char* key_str = *s;
+  switch (key_str[0]) {
+    case 'c':
+      if (strcmp(key_str, "cell") == 0) return CELL_SPACE;
+      if (strcmp(key_str, "code") == 0) return CODE_SPACE;
+      break;
+    case 'l':
+      if (strcmp(key_str, "lo") == 0) return LO_SPACE;
+      break;
+    case 'm':
+      if (strcmp(key_str, "map") == 0) return MAP_SPACE;
+      break;
+    case 'n':
+      if (strcmp(key_str, "new") == 0) return NEW_SPACE;
+      break;
+    case 'o':
+      if (strcmp(key_str, "old-pointer") == 0) return OLD_POINTER_SPACE;
+      if (strcmp(key_str, "old-data") == 0) return OLD_DATA_SPACE;
+      break;
+  }
+  return kInvalidSpace;
+}
+
+
+static bool InSpace(AllocationSpace space, HeapObject *heap_obj) {
+  if (space != LO_SPACE) {
+    return Heap::InSpace(heap_obj, space);
+  }
+
+  // This is an optimization to speed up the check for an object in the LO
+  // space by exclusion because we know that all object pointers passed in
+  // here are guaranteed to be in the heap.  Hence, it is safe to infer
+  // using an exclusion test.
+  // Note: calling Heap::InSpace(heap_obj, LO_SPACE) is too slow for our
+  // filters.
+  int first_space = static_cast<int>(FIRST_SPACE);
+  int last_space = static_cast<int>(LO_SPACE);
+  for (int sp = first_space; sp < last_space; sp++) {
+    if (Heap::InSpace(heap_obj, static_cast<AllocationSpace>(sp))) {
+      return false;
+    }
+  }
+  SLOW_ASSERT(Heap::InSpace(heap_obj, LO_SPACE));
+  return true;
+}
+
+
+static LiveObjectType FindTypeFor(String* type_str) {
+  SmartPointer<char> s =
+      type_str->ToCString(DISALLOW_NULLS, ROBUST_STRING_TRAVERSAL);
+
+#define CHECK_OBJECT_TYPE(type_, name) { \
+    const char* type_desc = GetObjectTypeDesc(kType##type_); \
+    const char* key_str = *s; \
+    if (strstr(type_desc, key_str) != NULL) return kType##type_; \
+  }
+  FOR_EACH_LIVE_OBJECT_TYPE(CHECK_OBJECT_TYPE)
+#undef CHECK_OBJECT_TYPE
+
+  return kInvalidLiveObjType;
+}
+
+
+class LolFilter {
+ public:
+  explicit LolFilter(Handle<JSObject> filter_obj);
+
+  inline bool is_active() const { return is_active_; }
+  inline bool Matches(HeapObject* obj) {
+    return !is_active() || MatchesSlow(obj);
+  }
+
+ private:
+  void InitTypeFilter(Handle<JSObject> filter_obj);
+  void InitSpaceFilter(Handle<JSObject> filter_obj);
+  void InitPropertyFilter(Handle<JSObject> filter_obj);
+  bool MatchesSlow(HeapObject* obj);
+
+  bool is_active_;
+  LiveObjectType type_;
+  AllocationSpace space_;
+  Handle<String> prop_;
+};
+
+
+LolFilter::LolFilter(Handle<JSObject> filter_obj)
+    : is_active_(false),
+      type_(kInvalidLiveObjType),
+      space_(kInvalidSpace),
+      prop_() {
+  if (filter_obj.is_null()) return;
+
+  InitTypeFilter(filter_obj);
+  InitSpaceFilter(filter_obj);
+  InitPropertyFilter(filter_obj);
+}
+
+
+void LolFilter::InitTypeFilter(Handle<JSObject> filter_obj) {
+  Handle<String> type_sym = Factory::LookupAsciiSymbol("type");
+  MaybeObject* maybe_result = filter_obj->GetProperty(*type_sym);
+  Object* type_obj;
+  if (maybe_result->ToObject(&type_obj)) {
+    if (type_obj->IsString()) {
+      String* type_str = String::cast(type_obj);
+      type_ = FindTypeFor(type_str);
+      if (type_ != kInvalidLiveObjType) {
+        is_active_ = true;
+      }
+    }
+  }
+}
+
+
+void LolFilter::InitSpaceFilter(Handle<JSObject> filter_obj) {
+  Handle<String> space_sym = Factory::LookupAsciiSymbol("space");
+  MaybeObject* maybe_result = filter_obj->GetProperty(*space_sym);
+  Object* space_obj;
+  if (maybe_result->ToObject(&space_obj)) {
+    if (space_obj->IsString()) {
+      String* space_str = String::cast(space_obj);
+      space_ = FindSpaceFor(space_str);
+      if (space_ != kInvalidSpace) {
+        is_active_ = true;
+      }
+    }
+  }
+}
+
+
+void LolFilter::InitPropertyFilter(Handle<JSObject> filter_obj) {
+  Handle<String> prop_sym = Factory::LookupAsciiSymbol("prop");
+  MaybeObject* maybe_result = filter_obj->GetProperty(*prop_sym);
+  Object* prop_obj;
+  if (maybe_result->ToObject(&prop_obj)) {
+    if (prop_obj->IsString()) {
+      prop_ = Handle<String>(String::cast(prop_obj));
+      is_active_ = true;
+    }
+  }
+}
+
+
+bool LolFilter::MatchesSlow(HeapObject* obj) {
+  if ((type_ != kInvalidLiveObjType) && !IsOfType(type_, obj)) {
+    return false;  // Fail because obj is not of the type of interest.
+  }
+  if ((space_ != kInvalidSpace) && !InSpace(space_, obj)) {
+    return false;  // Fail because obj is not in the space of interest.
+  }
+  if (!prop_.is_null() && obj->IsJSObject()) {
+    LookupResult result;
+    obj->Lookup(*prop_, &result);
+    if (!result.IsProperty()) {
+      return false;  // Fail because obj does not have the property of interest.
+    }
+  }
+  return true;
+}
+
+
+class LolIterator {
+ public:
+  LolIterator(LiveObjectList* older, LiveObjectList* newer)
+      : older_(older),
+        newer_(newer),
+        curr_(0),
+        elements_(0),
+        count_(0),
+        index_(0) { }
+
+  inline void Init() {
+    SetCurrent(newer_);
+    // If the elements_ list is empty, then move on to the next list as long
+    // as we're not at the last list (indicated by done()).
+    while ((elements_ == NULL) && !Done()) {
+      SetCurrent(curr_->prev_);
+    }
+  }
+
+  inline bool Done() const {
+    return (curr_ == older_);
+  }
+
+  // Object level iteration.
+  inline void Next() {
+    index_++;
+    if (index_ >= count_) {
+      // Iterate backwards until we get to the oldest list.
+      while (!Done()) {
+        SetCurrent(curr_->prev_);
+        // If we have elements to process, we're good to go.
+        if (elements_ != NULL) break;
+
+        // Else, we should advance to the next older list.
+      }
+    }
+  }
+
+  inline int Id() const {
+    return elements_[index_].id_;
+  }
+  inline HeapObject* Obj() const {
+    return elements_[index_].obj_;
+  }
+
+  inline int LolObjCount() const {
+    if (curr_ != NULL) return curr_->obj_count_;
+    return 0;
+  }
+
+ protected:
+  inline void SetCurrent(LiveObjectList* new_curr) {
+    curr_ = new_curr;
+    if (curr_ != NULL) {
+      elements_ = curr_->elements_;
+      count_ = curr_->obj_count_;
+      index_ = 0;
+    }
+  }
+
+  LiveObjectList* older_;
+  LiveObjectList* newer_;
+  LiveObjectList* curr_;
+  LiveObjectList::Element* elements_;
+  int count_;
+  int index_;
+};
+
+
+class LolForwardIterator : public LolIterator {
+ public:
+  LolForwardIterator(LiveObjectList* first, LiveObjectList* last)
+      : LolIterator(first, last) {
+  }
+
+  inline void Init() {
+    SetCurrent(older_);
+    // If the elements_ list is empty, then move on to the next list as long
+    // as we're not at the last list (indicated by Done()).
+    while ((elements_ == NULL) && !Done()) {
+      SetCurrent(curr_->next_);
+    }
+  }
+
+  inline bool Done() const {
+    return (curr_ == newer_);
+  }
+
+  // Object level iteration.
+  inline void Next() {
+    index_++;
+    if (index_ >= count_) {
+      // Done with current list.  Move on to the next.
+      while (!Done()) {  // If not at the last list already, ...
+        SetCurrent(curr_->next_);
+        // If we have elements to process, we're good to go.
+        if (elements_ != NULL) break;
+
+        // Else, we should advance to the next list.
+      }
+    }
+  }
+};
+
+
+// Minimizes the white space in a string.  Tabs and newlines are replaced
+// with a space where appropriate.
+static int CompactString(char* str) {
+  char* src = str;
+  char* dst = str;
+  char prev_ch = 0;
+  while (*dst != '\0') {
+    char ch = *src++;
+    // We will treat non-ascii chars as '?'.
+    if ((ch & 0x80) != 0) {
+      ch = '?';
+    }
+    // Compact contiguous whitespace chars into a single ' '.
+    if (isspace(ch)) {
+      if (prev_ch != ' ') *dst++ = ' ';
+      prev_ch = ' ';
+      continue;
+    }
+    *dst++ = ch;
+    prev_ch = ch;
+  }
+  return (dst - str);
+}
+
+
+// Generates a custom description based on the specific type of
+// object we're looking at.  We only generate specialized
+// descriptions where we can.  In all other cases, we emit the
+// generic info.
+static void GenerateObjectDesc(HeapObject* obj,
+                               char* buffer,
+                               int buffer_size) {
+  Vector<char> buffer_v(buffer, buffer_size);
+  ASSERT(obj != NULL);
+  if (obj->IsJSArray()) {
+    JSArray* jsarray = JSArray::cast(obj);
+    double length = jsarray->length()->Number();
+    OS::SNPrintF(buffer_v,
+                 "%p <%s> len %g",
+                 reinterpret_cast<void*>(obj),
+                 GetObjectTypeDesc(obj),
+                 length);
+
+  } else if (obj->IsString()) {
+    String *str = String::cast(obj);
+    // Only grab up to 160 chars in case they are double byte.
+    // We'll only dump 80 of them after we compact them.
+    const int kMaxCharToDump = 80;
+    const int kMaxBufferSize = kMaxCharToDump * 2;
+    SmartPointer<char> str_sp = str->ToCString(DISALLOW_NULLS,
+                                               ROBUST_STRING_TRAVERSAL,
+                                               0,
+                                               kMaxBufferSize);
+    char* str_cstr = *str_sp;
+    int length = CompactString(str_cstr);
+    OS::SNPrintF(buffer_v,
+                 "%p <%s> '%.80s%s'",
+                 reinterpret_cast<void*>(obj),
+                 GetObjectTypeDesc(obj),
+                 str_cstr,
+                 (length > kMaxCharToDump) ? "..." : "");
+
+  } else if (obj->IsJSFunction() || obj->IsSharedFunctionInfo()) {
+    SharedFunctionInfo* sinfo;
+    if (obj->IsJSFunction()) {
+      JSFunction* func = JSFunction::cast(obj);
+      sinfo = func->shared();
+    } else {
+      sinfo = SharedFunctionInfo::cast(obj);
+    }
+
+    String* name = sinfo->DebugName();
+    SmartPointer<char> name_sp =
+        name->ToCString(DISALLOW_NULLS, ROBUST_STRING_TRAVERSAL);
+    char* name_cstr = *name_sp;
+
+    HeapStringAllocator string_allocator;
+    StringStream stream(&string_allocator);
+    sinfo->SourceCodePrint(&stream, 50);
+    SmartPointer<const char> source_sp = stream.ToCString();
+    const char* source_cstr = *source_sp;
+
+    OS::SNPrintF(buffer_v,
+                 "%p <%s> '%s' %s",
+                 reinterpret_cast<void*>(obj),
+                 GetObjectTypeDesc(obj),
+                 name_cstr,
+                 source_cstr);
+
+  } else if (obj->IsFixedArray()) {
+    FixedArray* fixed = FixedArray::cast(obj);
+
+    OS::SNPrintF(buffer_v,
+                 "%p <%s> len %d",
+                 reinterpret_cast<void*>(obj),
+                 GetObjectTypeDesc(obj),
+                 fixed->length());
+
+  } else {
+    OS::SNPrintF(buffer_v,
+                 "%p <%s>",
+                 reinterpret_cast<void*>(obj),
+                 GetObjectTypeDesc(obj));
+  }
+}
+
+
+// Utility function for filling in a line of detail in a verbose dump.
+static bool AddObjDetail(Handle<FixedArray> arr,
+                         int index,
+                         int obj_id,
+                         Handle<HeapObject> target,
+                         const char* desc_str,
+                         Handle<String> id_sym,
+                         Handle<String> desc_sym,
+                         Handle<String> size_sym,
+                         Handle<JSObject> detail,
+                         Handle<String> desc,
+                         Handle<Object> error) {
+  detail = Factory::NewJSObject(Top::object_function());
+  if (detail->IsFailure()) {
+    error = detail;
+    return false;
+  }
+
+  int size = 0;
+  char buffer[512];
+  if (desc_str == NULL) {
+    ASSERT(!target.is_null());
+    HeapObject* obj = *target;
+    GenerateObjectDesc(obj, buffer, sizeof(buffer));
+    desc_str = buffer;
+    size = obj->Size();
+  }
+  desc = Factory::NewStringFromAscii(CStrVector(desc_str));
+  if (desc->IsFailure()) {
+    error = desc;
+    return false;
+  }
+
+  { MaybeObject* maybe_result = detail->SetProperty(*id_sym,
+                                                    Smi::FromInt(obj_id),
+                                                    NONE,
+                                                    kNonStrictMode);
+    if (maybe_result->IsFailure()) return false;
+  }
+  { MaybeObject* maybe_result = detail->SetProperty(*desc_sym,
+                                                    *desc,
+                                                    NONE,
+                                                    kNonStrictMode);
+    if (maybe_result->IsFailure()) return false;
+  }
+  { MaybeObject* maybe_result = detail->SetProperty(*size_sym,
+                                                    Smi::FromInt(size),
+                                                    NONE,
+                                                    kNonStrictMode);
+    if (maybe_result->IsFailure()) return false;
+  }
+
+  arr->set(index, *detail);
+  return true;
+}
+
+
+class DumpWriter {
+ public:
+  virtual ~DumpWriter() {}
+
+  virtual void ComputeTotalCountAndSize(LolFilter* filter,
+                                        int* count,
+                                        int* size) = 0;
+  virtual bool Write(Handle<FixedArray> elements_arr,
+                     int start,
+                     int dump_limit,
+                     LolFilter* filter,
+                     Handle<Object> error) = 0;
+};
+
+
+class LolDumpWriter: public DumpWriter {
+ public:
+  LolDumpWriter(LiveObjectList* older, LiveObjectList* newer)
+      : older_(older), newer_(newer) {
+  }
+
+  void ComputeTotalCountAndSize(LolFilter* filter, int* count, int* size) {
+    *count = 0;
+    *size = 0;
+
+    LolIterator it(older_, newer_);
+    for (it.Init(); !it.Done(); it.Next()) {
+      HeapObject* heap_obj = it.Obj();
+      if (!filter->Matches(heap_obj)) {
+        continue;
+      }
+
+      *size += heap_obj->Size();
+      (*count)++;
+    }
+  }
+
+  bool Write(Handle<FixedArray> elements_arr,
+             int start,
+             int dump_limit,
+             LolFilter* filter,
+             Handle<Object> error) {
+    // The lols are listed in latest to earliest.  We want to dump from
+    // earliest to latest.  So, compute the last element to start with.
+    int index = 0;
+    int count = 0;
+
+    // Prefetch some needed symbols.
+    Handle<String> id_sym = Factory::LookupAsciiSymbol("id");
+    Handle<String> desc_sym = Factory::LookupAsciiSymbol("desc");
+    Handle<String> size_sym = Factory::LookupAsciiSymbol("size");
+
+    // Fill the array with the lol object details.
+    Handle<JSObject> detail;
+    Handle<String> desc;
+    Handle<HeapObject> target;
+
+    LiveObjectList* first_lol = (older_ != NULL) ?
+                                older_->next_ : LiveObjectList::first_;
+    LiveObjectList* last_lol = (newer_ != NULL) ? newer_->next_ : NULL;
+
+    LolForwardIterator it(first_lol, last_lol);
+    for (it.Init(); !it.Done() && (index < dump_limit); it.Next()) {
+      HeapObject* heap_obj = it.Obj();
+
+      // Skip objects that have been filtered out.
+      if (!filter->Matches(heap_obj)) {
+        continue;
+      }
+
+      // Only report objects that are in the section of interest.
+      if (count >= start) {
+        target = Handle<HeapObject>(heap_obj);
+        bool success = AddObjDetail(elements_arr,
+                                    index++,
+                                    it.Id(),
+                                    target,
+                                    NULL,
+                                    id_sym,
+                                    desc_sym,
+                                    size_sym,
+                                    detail,
+                                    desc,
+                                    error);
+        if (!success) return false;
+      }
+      count++;
+    }
+    return true;
+  }
+
+ private:
+  LiveObjectList* older_;
+  LiveObjectList* newer_;
+};
+
+
+class RetainersDumpWriter: public DumpWriter {
+ public:
+  RetainersDumpWriter(Handle<HeapObject> target,
+                      Handle<JSObject> instance_filter,
+                      Handle<JSFunction> args_function)
+      : target_(target),
+        instance_filter_(instance_filter),
+        args_function_(args_function) {
+  }
+
+  void ComputeTotalCountAndSize(LolFilter* filter, int* count, int* size) {
+    Handle<FixedArray> retainers_arr;
+    Handle<Object> error;
+
+    *size = -1;
+    LiveObjectList::GetRetainers(target_,
+                                 instance_filter_,
+                                 retainers_arr,
+                                 0,
+                                 Smi::kMaxValue,
+                                 count,
+                                 filter,
+                                 NULL,
+                                 *args_function_,
+                                 error);
+  }
+
+  bool Write(Handle<FixedArray> elements_arr,
+             int start,
+             int dump_limit,
+             LolFilter* filter,
+             Handle<Object> error) {
+    int dummy;
+    int count;
+
+    // Fill the retainer objects.
+    count = LiveObjectList::GetRetainers(target_,
+                                         instance_filter_,
+                                         elements_arr,
+                                         start,
+                                         dump_limit,
+                                         &dummy,
+                                         filter,
+                                         NULL,
+                                         *args_function_,
+                                         error);
+    if (count < 0) {
+        return false;
+    }
+    return true;
+  }
+
+ private:
+  Handle<HeapObject> target_;
+  Handle<JSObject> instance_filter_;
+  Handle<JSFunction> args_function_;
+};
+
+
+class LiveObjectSummary {
+ public:
+  explicit LiveObjectSummary(LolFilter* filter)
+      : total_count_(0),
+        total_size_(0),
+        found_root_(false),
+        found_weak_root_(false),
+        filter_(filter) {
+    memset(counts_, 0, sizeof(counts_[0]) * kNumberOfEntries);
+    memset(sizes_, 0, sizeof(sizes_[0]) * kNumberOfEntries);
+  }
+
+  void Add(HeapObject* heap_obj) {
+    int size = heap_obj->Size();
+    LiveObjectType type = GetObjectType(heap_obj);
+    ASSERT(type != kInvalidLiveObjType);
+    counts_[type]++;
+    sizes_[type] += size;
+    total_count_++;
+    total_size_ += size;
+  }
+
+  void set_found_root() { found_root_ = true; }
+  void set_found_weak_root() { found_weak_root_ = true; }
+
+  inline int Count(LiveObjectType type) {
+    return counts_[type];
+  }
+  inline int Size(LiveObjectType type) {
+    return sizes_[type];
+  }
+  inline int total_count() {
+    return total_count_;
+  }
+  inline int total_size() {
+    return total_size_;
+  }
+  inline bool found_root() {
+    return found_root_;
+  }
+  inline bool found_weak_root() {
+    return found_weak_root_;
+  }
+  int GetNumberOfEntries() {
+    int entries = 0;
+    for (int i = 0; i < kNumberOfEntries; i++) {
+      if (counts_[i]) entries++;
+    }
+    return entries;
+  }
+
+  inline LolFilter* filter() { return filter_; }
+
+  static const int kNumberOfEntries = kNumberOfTypes;
+
+ private:
+  int counts_[kNumberOfEntries];
+  int sizes_[kNumberOfEntries];
+  int total_count_;
+  int total_size_;
+  bool found_root_;
+  bool found_weak_root_;
+
+  LolFilter *filter_;
+};
+
+
+// Abstraction for a summary writer.
+class SummaryWriter {
+ public:
+  virtual ~SummaryWriter() {}
+  virtual void Write(LiveObjectSummary* summary) = 0;
+};
+
+
+// A summary writer for filling in a summary of lol lists and diffs.
+class LolSummaryWriter: public SummaryWriter {
+ public:
+  LolSummaryWriter(LiveObjectList *older_lol,
+                   LiveObjectList *newer_lol)
+      : older_(older_lol), newer_(newer_lol) {
+  }
+
+  void Write(LiveObjectSummary* summary) {
+    LolFilter* filter = summary->filter();
+
+    // Fill the summary with the lol object details.
+    LolIterator it(older_, newer_);
+    for (it.Init(); !it.Done(); it.Next()) {
+      HeapObject* heap_obj = it.Obj();
+      if (!filter->Matches(heap_obj)) {
+        continue;
+      }
+      summary->Add(heap_obj);
+    }
+  }
+
+ private:
+  LiveObjectList* older_;
+  LiveObjectList* newer_;
+};
+
+
+// A summary writer for filling in a retainers list.
+class RetainersSummaryWriter: public SummaryWriter {
+ public:
+  RetainersSummaryWriter(Handle<HeapObject> target,
+                         Handle<JSObject> instance_filter,
+                         Handle<JSFunction> args_function)
+      : target_(target),
+        instance_filter_(instance_filter),
+        args_function_(args_function) {
+  }
+
+  void Write(LiveObjectSummary* summary) {
+    Handle<FixedArray> retainers_arr;
+    Handle<Object> error;
+    int dummy_total_count;
+    LiveObjectList::GetRetainers(target_,
+                                 instance_filter_,
+                                 retainers_arr,
+                                 0,
+                                 Smi::kMaxValue,
+                                 &dummy_total_count,
+                                 summary->filter(),
+                                 summary,
+                                 *args_function_,
+                                 error);
+  }
+
+ private:
+  Handle<HeapObject> target_;
+  Handle<JSObject> instance_filter_;
+  Handle<JSFunction> args_function_;
+};
+
+
+uint32_t LiveObjectList::next_element_id_ = 1;
+int LiveObjectList::list_count_ = 0;
+int LiveObjectList::last_id_ = 0;
+LiveObjectList* LiveObjectList::first_ = NULL;
+LiveObjectList* LiveObjectList::last_ = NULL;
+
+
+LiveObjectList::LiveObjectList(LiveObjectList* prev, int capacity)
+    : prev_(prev),
+      next_(NULL),
+      capacity_(capacity),
+      obj_count_(0) {
+  elements_ = NewArray<Element>(capacity);
+  id_ = ++last_id_;
+
+  list_count_++;
+}
+
+
+LiveObjectList::~LiveObjectList() {
+  DeleteArray<Element>(elements_);
+  delete prev_;
+}
+
+
+int LiveObjectList::GetTotalObjCountAndSize(int* size_p) {
+  int size = 0;
+  int count = 0;
+  LiveObjectList *lol = this;
+  do {
+    // Only compute total size if requested i.e. when size_p is not null.
+    if (size_p != NULL) {
+      Element* elements = lol->elements_;
+      for (int i = 0; i < lol->obj_count_; i++) {
+        HeapObject* heap_obj = elements[i].obj_;
+        size += heap_obj->Size();
+      }
+    }
+    count += lol->obj_count_;
+    lol = lol->prev_;
+  } while (lol != NULL);
+
+  if (size_p != NULL) {
+    *size_p = size;
+  }
+  return count;
+}
+
+
+// Adds an object to the lol.
+// Returns true if successful, else returns false.
+bool LiveObjectList::Add(HeapObject* obj) {
+  // If the object is already accounted for in the prev list which we inherit
+  // from, then no need to add it to this list.
+  if ((prev() != NULL) && (prev()->Find(obj) != NULL)) {
+    return true;
+  }
+  ASSERT(obj_count_ <= capacity_);
+  if (obj_count_ == capacity_) {
+    // The heap must have grown and we have more objects than capacity to store
+    // them.
+    return false;  // Fail this addition.
+  }
+  Element& element = elements_[obj_count_++];
+  element.id_ = next_element_id_++;
+  element.obj_ = obj;
+  return true;
+}
+
+
+// Comparator used for sorting and searching the lol.
+int LiveObjectList::CompareElement(const Element* a, const Element* b) {
+  const HeapObject* obj1 = a->obj_;
+  const HeapObject* obj2 = b->obj_;
+  // For lol elements, it doesn't matter which comes first if 2 elements point
+  // to the same object (which gets culled later).  Hence, we only care about
+  // the the greater than / less than relationships.
+  return (obj1 > obj2) ? 1 : (obj1 == obj2) ? 0 : -1;
+}
+
+
+// Looks for the specified object in the lol, and returns its element if found.
+LiveObjectList::Element* LiveObjectList::Find(HeapObject* obj) {
+  LiveObjectList* lol = this;
+  Element key;
+  Element* result = NULL;
+
+  key.obj_ = obj;
+  // Iterate through the chain of lol's to look for the object.
+  while ((result == NULL) && (lol != NULL)) {
+    result = reinterpret_cast<Element*>(
+        bsearch(&key, lol->elements_, lol->obj_count_,
+                sizeof(Element),
+                reinterpret_cast<RawComparer>(CompareElement)));
+    lol = lol->prev_;
+  }
+  return result;
+}
+
+
+// "Nullifies" (convert the HeapObject* into an SMI) so that it will get cleaned
+// up in the GCEpilogue, while preserving the sort order of the lol.
+// NOTE: the lols need to be already sorted before NullifyMostRecent() is
+// called.
+void LiveObjectList::NullifyMostRecent(HeapObject* obj) {
+  LiveObjectList* lol = last();
+  Element key;
+  Element* result = NULL;
+
+  key.obj_ = obj;
+  // Iterate through the chain of lol's to look for the object.
+  while (lol != NULL) {
+    result = reinterpret_cast<Element*>(
+        bsearch(&key, lol->elements_, lol->obj_count_,
+                sizeof(Element),
+                reinterpret_cast<RawComparer>(CompareElement)));
+    if (result != NULL) {
+      // Since there may be more than one (we are nullifying dup's after all),
+      // find the first in the current lol, and nullify that.  The lol should
+      // be sorted already to make this easy (see the use of SortAll()).
+      int i = result - lol->elements_;
+
+      // NOTE: we sort the lol in increasing order.  So, if an object has been
+      // "nullified" (its lowest bit will be cleared to make it look like an
+      // SMI), it would/should show up before the equivalent dups that have not
+      // yet been "nullified".  Hence, we should be searching backwards for the
+      // first occurence of a matching object and nullify that instance.  This
+      // will ensure that we preserve the expected sorting order.
+      for (i--; i > 0; i--) {
+        Element* element = &lol->elements_[i];
+        HeapObject* curr_obj = element->obj_;
+        if (curr_obj != obj) {
+            break;  // No more matches.  Let's move on.
+        }
+        result = element;  // Let this earlier match be the result.
+      }
+
+      // Nullify the object.
+      NullifyNonLivePointer(&result->obj_);
+      return;
+    }
+    lol = lol->prev_;
+  }
+}
+
+
+// Sorts the lol.
+void LiveObjectList::Sort() {
+  if (obj_count_ > 0) {
+    Vector<Element> elements_v(elements_, obj_count_);
+    elements_v.Sort(CompareElement);
+  }
+}
+
+
+// Sorts all captured lols starting from the latest.
+void LiveObjectList::SortAll() {
+  LiveObjectList* lol = last();
+  while (lol != NULL) {
+    lol->Sort();
+    lol = lol->prev_;
+  }
+}
+
+
+// Counts the number of objects in the heap.
+static int CountHeapObjects() {
+  int count = 0;
+  // Iterate over all the heap spaces and count the number of objects.
+  HeapIterator iterator(HeapIterator::kFilterFreeListNodes);
+  HeapObject* heap_obj = NULL;
+  while ((heap_obj = iterator.next()) != NULL) {
+    count++;
+  }
+  return count;
+}
+
+
+// Captures a current snapshot of all objects in the heap.
+MaybeObject* LiveObjectList::Capture() {
+  HandleScope scope;
+
+  // Count the number of objects in the heap.
+  int total_count = CountHeapObjects();
+  int count = total_count;
+  int size = 0;
+
+  LiveObjectList* last_lol = last();
+  if (last_lol != NULL) {
+    count -= last_lol->TotalObjCount();
+  }
+
+  LiveObjectList* lol;
+
+  // Create a lol large enough to track all the objects.
+  lol = new LiveObjectList(last_lol, count);
+  if (lol == NULL) {
+    return NULL;  // No memory to proceed.
+  }
+
+  // The HeapIterator needs to be in its own scope because it disables
+  // allocation, and we need allocate below.
+  {
+    // Iterate over all the heap spaces and add the objects.
+    HeapIterator iterator(HeapIterator::kFilterFreeListNodes);
+    HeapObject* heap_obj = NULL;
+    bool failed = false;
+    while (!failed && (heap_obj = iterator.next()) != NULL) {
+      failed = !lol->Add(heap_obj);
+      size += heap_obj->Size();
+    }
+    ASSERT(!failed);
+
+    lol->Sort();
+
+    // Add the current lol to the list of lols.
+    if (last_ != NULL) {
+      last_->next_ = lol;
+    } else {
+      first_ = lol;
+    }
+    last_ = lol;
+
+#ifdef VERIFY_LOL
+    if (FLAG_verify_lol) {
+      Verify(true);
+    }
+#endif
+  }
+
+  Handle<String> id_sym = Factory::LookupAsciiSymbol("id");
+  Handle<String> count_sym = Factory::LookupAsciiSymbol("count");
+  Handle<String> size_sym = Factory::LookupAsciiSymbol("size");
+
+  Handle<JSObject> result = Factory::NewJSObject(Top::object_function());
+  if (result->IsFailure()) return Object::cast(*result);
+
+  { MaybeObject* maybe_result = result->SetProperty(*id_sym,
+                                                    Smi::FromInt(lol->id()),
+                                                    NONE,
+                                                    kNonStrictMode);
+    if (maybe_result->IsFailure()) return maybe_result;
+  }
+  { MaybeObject* maybe_result = result->SetProperty(*count_sym,
+                                                    Smi::FromInt(total_count),
+                                                    NONE,
+                                                    kNonStrictMode);
+    if (maybe_result->IsFailure()) return maybe_result;
+  }
+  { MaybeObject* maybe_result = result->SetProperty(*size_sym,
+                                                    Smi::FromInt(size),
+                                                    NONE,
+                                                    kNonStrictMode);
+    if (maybe_result->IsFailure()) return maybe_result;
+  }
+
+  return *result;
+}
+
+
+// Delete doesn't actually deletes an lol.  It just marks it as invisible since
+// its contents are considered to be part of subsequent lists as well.  The
+// only time we'll actually delete the lol is when we Reset() or if the lol is
+// invisible, and its element count reaches 0.
+bool LiveObjectList::Delete(int id) {
+  LiveObjectList *lol = last();
+  while (lol != NULL) {
+    if (lol->id() == id) {
+      break;
+    }
+    lol = lol->prev_;
+  }
+
+  // If no lol is found for this id, then we fail to delete.
+  if (lol == NULL) return false;
+
+  // Else, mark the lol as invisible i.e. id == 0.
+  lol->id_ = 0;
+  list_count_--;
+  ASSERT(list_count_ >= 0);
+  if (lol->obj_count_ == 0) {
+    // Point the next lol's prev to this lol's prev.
+    LiveObjectList* next = lol->next_;
+    LiveObjectList* prev = lol->prev_;
+    // Point next's prev to prev.
+    if (next != NULL) {
+      next->prev_ = lol->prev_;
+    } else {
+      last_ = lol->prev_;
+    }
+    // Point prev's next to next.
+    if (prev != NULL) {
+      prev->next_ = lol->next_;
+    } else {
+      first_ = lol->next_;
+    }
+
+    lol->prev_ = NULL;
+    lol->next_ = NULL;
+
+    // Delete this now empty and invisible lol.
+    delete lol;
+  }
+
+  // Just in case we've marked everything invisible, then clean up completely.
+  if (list_count_ == 0) {
+    Reset();
+  }
+
+  return true;
+}
+
+
+MaybeObject* LiveObjectList::Dump(int older_id,
+                                  int newer_id,
+                                  int start_idx,
+                                  int dump_limit,
+                                  Handle<JSObject> filter_obj) {
+  if ((older_id < 0) || (newer_id < 0) || (last() == NULL)) {
+    return Failure::Exception();  // Fail: 0 is not a valid lol id.
+  }
+  if (newer_id < older_id) {
+    // They are not in the expected order.  Swap them.
+    int temp = older_id;
+    older_id = newer_id;
+    newer_id = temp;
+  }
+
+  LiveObjectList *newer_lol = FindLolForId(newer_id, last());
+  LiveObjectList *older_lol = FindLolForId(older_id, newer_lol);
+
+  // If the id is defined, and we can't find a LOL for it, then we have an
+  // invalid id.
+  if ((newer_id != 0) && (newer_lol == NULL)) {
+    return Failure::Exception();  // Fail: the newer lol id is invalid.
+  }
+  if ((older_id != 0) && (older_lol == NULL)) {
+    return Failure::Exception();  // Fail: the older lol id is invalid.
+  }
+
+  LolFilter filter(filter_obj);
+  LolDumpWriter writer(older_lol, newer_lol);
+  return DumpPrivate(&writer, start_idx, dump_limit, &filter);
+}
+
+
+MaybeObject* LiveObjectList::DumpPrivate(DumpWriter* writer,
+                                         int start,
+                                         int dump_limit,
+                                         LolFilter* filter) {
+  HandleScope scope;
+
+  // Calculate the number of entries of the dump.
+  int count = -1;
+  int size = -1;
+  writer->ComputeTotalCountAndSize(filter, &count, &size);
+
+  // Adjust for where to start the dump.
+  if ((start < 0) || (start >= count)) {
+    return Failure::Exception();  // invalid start.
+  }
+
+  int remaining_count = count - start;
+  if (dump_limit > remaining_count) {
+    dump_limit = remaining_count;
+  }
+
+  // Allocate an array to hold the result.
+  Handle<FixedArray> elements_arr = Factory::NewFixedArray(dump_limit);
+  if (elements_arr->IsFailure()) return Object::cast(*elements_arr);
+
+  // Fill in the dump.
+  Handle<Object> error;
+  bool success = writer->Write(elements_arr,
+                               start,
+                               dump_limit,
+                               filter,
+                               error);
+  if (!success) return Object::cast(*error);
+
+  MaybeObject* maybe_result;
+
+  // Allocate the result body.
+  Handle<JSObject> body = Factory::NewJSObject(Top::object_function());
+  if (body->IsFailure()) return Object::cast(*body);
+
+  // Set the updated body.count.
+  Handle<String> count_sym = Factory::LookupAsciiSymbol("count");
+  maybe_result = body->SetProperty(*count_sym,
+                                   Smi::FromInt(count),
+                                   NONE,
+                                   kNonStrictMode);
+  if (maybe_result->IsFailure()) return maybe_result;
+
+  // Set the updated body.size if appropriate.
+  if (size >= 0) {
+    Handle<String> size_sym = Factory::LookupAsciiSymbol("size");
+    maybe_result = body->SetProperty(*size_sym,
+                                     Smi::FromInt(size),
+                                     NONE,
+                                     kNonStrictMode);
+    if (maybe_result->IsFailure()) return maybe_result;
+  }
+
+  // Set body.first_index.
+  Handle<String> first_sym = Factory::LookupAsciiSymbol("first_index");
+  maybe_result = body->SetProperty(*first_sym,
+                                   Smi::FromInt(start),
+                                   NONE,
+                                   kNonStrictMode);
+  if (maybe_result->IsFailure()) return maybe_result;
+
+  // Allocate the JSArray of the elements.
+  Handle<JSObject> elements = Factory::NewJSObject(Top::array_function());
+  if (elements->IsFailure()) return Object::cast(*elements);
+  Handle<JSArray>::cast(elements)->SetContent(*elements_arr);
+
+  // Set body.elements.
+  Handle<String> elements_sym = Factory::LookupAsciiSymbol("elements");
+  maybe_result = body->SetProperty(*elements_sym,
+                                   *elements,
+                                   NONE,
+                                   kNonStrictMode);
+  if (maybe_result->IsFailure()) return maybe_result;
+
+  return *body;
+}
+
+
+MaybeObject* LiveObjectList::Summarize(int older_id,
+                                       int newer_id,
+                                       Handle<JSObject> filter_obj) {
+  if ((older_id < 0) || (newer_id < 0) || (last() == NULL)) {
+    return Failure::Exception();  // Fail: 0 is not a valid lol id.
+  }
+  if (newer_id < older_id) {
+    // They are not in the expected order.  Swap them.
+    int temp = older_id;
+    older_id = newer_id;
+    newer_id = temp;
+  }
+
+  LiveObjectList *newer_lol = FindLolForId(newer_id, last());
+  LiveObjectList *older_lol = FindLolForId(older_id, newer_lol);
+
+  // If the id is defined, and we can't find a LOL for it, then we have an
+  // invalid id.
+  if ((newer_id != 0) && (newer_lol == NULL)) {
+    return Failure::Exception();  // Fail: the newer lol id is invalid.
+  }
+  if ((older_id != 0) && (older_lol == NULL)) {
+    return Failure::Exception();  // Fail: the older lol id is invalid.
+  }
+
+  LolFilter filter(filter_obj);
+  LolSummaryWriter writer(older_lol, newer_lol);
+  return SummarizePrivate(&writer, &filter, false);
+}
+
+
+// Creates a summary report for the debugger.
+// Note: the SummaryWriter takes care of iterating over objects and filling in
+// the summary.
+MaybeObject* LiveObjectList::SummarizePrivate(SummaryWriter* writer,
+                                              LolFilter* filter,
+                                              bool is_tracking_roots) {
+  HandleScope scope;
+  MaybeObject* maybe_result;
+
+  LiveObjectSummary summary(filter);
+  writer->Write(&summary);
+
+  // The result body will look like this:
+  // body: {
+  //   count: <total_count>,
+  //   size: <total_size>,
+  //   found_root: <boolean>,       // optional.
+  //   found_weak_root: <boolean>,  // optional.
+  //   summary: [
+  //     {
+  //       desc: "<object type name>",
+  //       count: <count>,
+  //       size: size
+  //     },
+  //     ...
+  //   ]
+  // }
+
+  // Prefetch some needed symbols.
+  Handle<String> desc_sym = Factory::LookupAsciiSymbol("desc");
+  Handle<String> count_sym = Factory::LookupAsciiSymbol("count");
+  Handle<String> size_sym = Factory::LookupAsciiSymbol("size");
+  Handle<String> summary_sym = Factory::LookupAsciiSymbol("summary");
+
+  // Allocate the summary array.
+  int entries_count = summary.GetNumberOfEntries();
+  Handle<FixedArray> summary_arr =
+      Factory::NewFixedArray(entries_count);
+  if (summary_arr->IsFailure()) return Object::cast(*summary_arr);
+
+  int idx = 0;
+  for (int i = 0; i < LiveObjectSummary::kNumberOfEntries; i++) {
+    // Allocate the summary record.
+    Handle<JSObject> detail = Factory::NewJSObject(Top::object_function());
+    if (detail->IsFailure()) return Object::cast(*detail);
+
+    // Fill in the summary record.
+    LiveObjectType type = static_cast<LiveObjectType>(i);
+    int count = summary.Count(type);
+    if (count) {
+      const char* desc_cstr = GetObjectTypeDesc(type);
+      Handle<String> desc = Factory::LookupAsciiSymbol(desc_cstr);
+      int size = summary.Size(type);
+
+      maybe_result = detail->SetProperty(*desc_sym,
+                                         *desc,
+                                         NONE,
+                                         kNonStrictMode);
+      if (maybe_result->IsFailure()) return maybe_result;
+      maybe_result = detail->SetProperty(*count_sym,
+                                         Smi::FromInt(count),
+                                         NONE,
+                                         kNonStrictMode);
+      if (maybe_result->IsFailure()) return maybe_result;
+      maybe_result = detail->SetProperty(*size_sym,
+                                         Smi::FromInt(size),
+                                         NONE,
+                                         kNonStrictMode);
+      if (maybe_result->IsFailure()) return maybe_result;
+
+      summary_arr->set(idx++, *detail);
+    }
+  }
+
+  // Wrap the summary fixed array in a JS array.
+  Handle<JSObject> summary_obj = Factory::NewJSObject(Top::array_function());
+  if (summary_obj->IsFailure()) return Object::cast(*summary_obj);
+  Handle<JSArray>::cast(summary_obj)->SetContent(*summary_arr);
+
+  // Create the body object.
+  Handle<JSObject> body = Factory::NewJSObject(Top::object_function());
+  if (body->IsFailure()) return Object::cast(*body);
+
+  // Fill out the body object.
+  int total_count = summary.total_count();
+  int total_size = summary.total_size();
+  maybe_result = body->SetProperty(*count_sym,
+                                   Smi::FromInt(total_count),
+                                   NONE,
+                                   kNonStrictMode);
+  if (maybe_result->IsFailure()) return maybe_result;
+
+  maybe_result = body->SetProperty(*size_sym,
+                                   Smi::FromInt(total_size),
+                                   NONE,
+                                   kNonStrictMode);
+  if (maybe_result->IsFailure()) return maybe_result;
+
+  if (is_tracking_roots) {
+    int found_root = summary.found_root();
+    int found_weak_root = summary.found_weak_root();
+    Handle<String> root_sym = Factory::LookupAsciiSymbol("found_root");
+    Handle<String> weak_root_sym =
+        Factory::LookupAsciiSymbol("found_weak_root");
+    maybe_result = body->SetProperty(*root_sym,
+                                     Smi::FromInt(found_root),
+                                     NONE,
+                                     kNonStrictMode);
+    if (maybe_result->IsFailure()) return maybe_result;
+    maybe_result = body->SetProperty(*weak_root_sym,
+                                     Smi::FromInt(found_weak_root),
+                                     NONE,
+                                     kNonStrictMode);
+    if (maybe_result->IsFailure()) return maybe_result;
+  }
+
+  maybe_result = body->SetProperty(*summary_sym,
+                                   *summary_obj,
+                                   NONE,
+                                   kNonStrictMode);
+  if (maybe_result->IsFailure()) return maybe_result;
+
+  return *body;
+}
+
+
+// Returns an array listing the captured lols.
+// Note: only dumps the section starting at start_idx and only up to
+// dump_limit entries.
+MaybeObject* LiveObjectList::Info(int start_idx, int dump_limit) {
+  HandleScope scope;
+  MaybeObject* maybe_result;
+
+  int total_count = LiveObjectList::list_count();
+  int dump_count = total_count;
+
+  // Adjust for where to start the dump.
+  if (total_count == 0) {
+      start_idx = 0;  // Ensure this to get an empty list.
+  } else if ((start_idx < 0) || (start_idx >= total_count)) {
+    return Failure::Exception();  // invalid start.
+  }
+  dump_count -= start_idx;
+
+  // Adjust for the dump limit.
+  if (dump_count > dump_limit) {
+    dump_count = dump_limit;
+  }
+
+  // Allocate an array to hold the result.
+  Handle<FixedArray> list = Factory::NewFixedArray(dump_count);
+  if (list->IsFailure()) return Object::cast(*list);
+
+  // Prefetch some needed symbols.
+  Handle<String> id_sym = Factory::LookupAsciiSymbol("id");
+  Handle<String> count_sym = Factory::LookupAsciiSymbol("count");
+  Handle<String> size_sym = Factory::LookupAsciiSymbol("size");
+
+  // Fill the array with the lol details.
+  int idx = 0;
+  LiveObjectList* lol = first_;
+  while ((lol != NULL) && (idx < start_idx)) {  // Skip tail entries.
+    if (lol->id() != 0) {
+      idx++;
+    }
+    lol = lol->next();
+  }
+  idx = 0;
+  while ((lol != NULL) && (dump_limit != 0)) {
+    if (lol->id() != 0) {
+      int count;
+      int size;
+      count = lol->GetTotalObjCountAndSize(&size);
+
+      Handle<JSObject> detail = Factory::NewJSObject(Top::object_function());
+      if (detail->IsFailure()) return Object::cast(*detail);
+
+      maybe_result = detail->SetProperty(*id_sym,
+                                         Smi::FromInt(lol->id()),
+                                         NONE,
+                                         kNonStrictMode);
+      if (maybe_result->IsFailure()) return maybe_result;
+      maybe_result = detail->SetProperty(*count_sym,
+                                         Smi::FromInt(count),
+                                         NONE,
+                                         kNonStrictMode);
+      if (maybe_result->IsFailure()) return maybe_result;
+      maybe_result = detail->SetProperty(*size_sym,
+                                         Smi::FromInt(size),
+                                         NONE,
+                                         kNonStrictMode);
+      if (maybe_result->IsFailure()) return maybe_result;
+      list->set(idx++, *detail);
+      dump_limit--;
+    }
+    lol = lol->next();
+  }
+
+  // Return the result as a JS array.
+  Handle<JSObject> lols = Factory::NewJSObject(Top::array_function());
+  Handle<JSArray>::cast(lols)->SetContent(*list);
+
+  Handle<JSObject> result = Factory::NewJSObject(Top::object_function());
+  if (result->IsFailure()) return Object::cast(*result);
+
+  maybe_result = result->SetProperty(*count_sym,
+                                     Smi::FromInt(total_count),
+                                     NONE,
+                                     kNonStrictMode);
+  if (maybe_result->IsFailure()) return maybe_result;
+
+  Handle<String> first_sym = Factory::LookupAsciiSymbol("first_index");
+  maybe_result = result->SetProperty(*first_sym,
+                                     Smi::FromInt(start_idx),
+                                     NONE,
+                                     kNonStrictMode);
+  if (maybe_result->IsFailure()) return maybe_result;
+
+  Handle<String> lists_sym = Factory::LookupAsciiSymbol("lists");
+  maybe_result = result->SetProperty(*lists_sym,
+                                     *lols,
+                                     NONE,
+                                     kNonStrictMode);
+  if (maybe_result->IsFailure()) return maybe_result;
+
+  return *result;
+}
+
+
+// Deletes all captured lols.
+void LiveObjectList::Reset() {
+  LiveObjectList *lol = last();
+  // Just delete the last.  Each lol will delete it's prev automatically.
+  delete lol;
+
+  next_element_id_ = 1;
+  list_count_ = 0;
+  last_id_ = 0;
+  first_ = NULL;
+  last_ = NULL;
+}
+
+
+// Gets the object for the specified obj id.
+Object* LiveObjectList::GetObj(int obj_id) {
+  Element* element = FindElementFor<int>(GetElementId, obj_id);
+  if (element != NULL) {
+    return Object::cast(element->obj_);
+  }
+  return Heap::undefined_value();
+}
+
+
+// Gets the obj id for the specified address if valid.
+int LiveObjectList::GetObjId(Object* obj) {
+  // Make a heap object pointer from the address.
+  HeapObject* hobj = HeapObject::cast(obj);
+  Element* element = FindElementFor<HeapObject*>(GetElementObj, hobj);
+  if (element != NULL) {
+    return element->id_;
+  }
+  return 0;  // Invalid address.
+}
+
+
+// Gets the obj id for the specified address if valid.
+Object* LiveObjectList::GetObjId(Handle<String> address) {
+  SmartPointer<char> addr_str =
+      address->ToCString(DISALLOW_NULLS, ROBUST_STRING_TRAVERSAL);
+
+  // Extract the address value from the string.
+  int value = static_cast<int>(StringToInt(*address, 16));
+  Object* obj = reinterpret_cast<Object*>(value);
+  return Smi::FromInt(GetObjId(obj));
+}
+
+
+// Helper class for copying HeapObjects.
+class LolVisitor: public ObjectVisitor {
+ public:
+
+  LolVisitor(HeapObject* target, Handle<HeapObject> handle_to_skip)
+      : target_(target), handle_to_skip_(handle_to_skip), found_(false) {}
+
+  void VisitPointer(Object** p) { CheckPointer(p); }
+
+  void VisitPointers(Object** start, Object** end) {
+    // Check all HeapObject pointers in [start, end).
+    for (Object** p = start; !found() && p < end; p++) CheckPointer(p);
+  }
+
+  inline bool found() const { return found_; }
+  inline bool reset() { return found_ = false; }
+
+ private:
+  inline void CheckPointer(Object** p) {
+    Object* object = *p;
+    if (HeapObject::cast(object) == target_) {
+      // We may want to skip this handle because the handle may be a local
+      // handle in a handle scope in one of our callers.  Once we return,
+      // that handle will be popped.  Hence, we don't want to count it as
+      // a root that would have kept the target object alive.
+      if (!handle_to_skip_.is_null() &&
+          handle_to_skip_.location() == reinterpret_cast<HeapObject**>(p)) {
+        return;  // Skip this handle.
+      }
+      found_ = true;
+    }
+  }
+
+  HeapObject* target_;
+  Handle<HeapObject> handle_to_skip_;
+  bool found_;
+};
+
+
+inline bool AddRootRetainerIfFound(const LolVisitor& visitor,
+                                   LolFilter* filter,
+                                   LiveObjectSummary *summary,
+                                   void (*SetRootFound)(LiveObjectSummary *s),
+                                   int start,
+                                   int dump_limit,
+                                   int* total_count,
+                                   Handle<FixedArray> retainers_arr,
+                                   int* count,
+                                   int* index,
+                                   const char* root_name,
+                                   Handle<String> id_sym,
+                                   Handle<String> desc_sym,
+                                   Handle<String> size_sym,
+                                   Handle<Object> error) {
+  HandleScope scope;
+
+  // Scratch handles.
+  Handle<JSObject> detail;
+  Handle<String> desc;
+  Handle<HeapObject> retainer;
+
+  if (visitor.found()) {
+    if (!filter->is_active()) {
+      (*total_count)++;
+      if (summary) {
+        SetRootFound(summary);
+      } else if ((*total_count > start) && ((*index) < dump_limit)) {
+        (*count)++;
+        if (!retainers_arr.is_null()) {
+          return AddObjDetail(retainers_arr,
+                              (*index)++,
+                              0,
+                              retainer,
+                              root_name,
+                              id_sym,
+                              desc_sym,
+                              size_sym,
+                              detail,
+                              desc,
+                              error);
+        }
+      }
+    }
+  }
+  return true;
+}
+
+
+inline void SetFoundRoot(LiveObjectSummary *summary) {
+  summary->set_found_root();
+}
+
+
+inline void SetFoundWeakRoot(LiveObjectSummary *summary) {
+  summary->set_found_weak_root();
+}
+
+
+int LiveObjectList::GetRetainers(Handle<HeapObject> target,
+                                 Handle<JSObject> instance_filter,
+                                 Handle<FixedArray> retainers_arr,
+                                 int start,
+                                 int dump_limit,
+                                 int* total_count,
+                                 LolFilter* filter,
+                                 LiveObjectSummary *summary,
+                                 JSFunction* arguments_function,
+                                 Handle<Object> error) {
+  HandleScope scope;
+
+  // Scratch handles.
+  Handle<JSObject> detail;
+  Handle<String> desc;
+  Handle<HeapObject> retainer;
+
+  // Prefetch some needed symbols.
+  Handle<String> id_sym = Factory::LookupAsciiSymbol("id");
+  Handle<String> desc_sym = Factory::LookupAsciiSymbol("desc");
+  Handle<String> size_sym = Factory::LookupAsciiSymbol("size");
+
+  NoHandleAllocation ha;
+  int count = 0;
+  int index = 0;
+  Handle<JSObject> last_obj;
+
+  *total_count = 0;
+
+  // Iterate roots.
+  LolVisitor lol_visitor(*target, target);
+  Heap::IterateStrongRoots(&lol_visitor, VISIT_ALL);
+  if (!AddRootRetainerIfFound(lol_visitor,
+                              filter,
+                              summary,
+                              SetFoundRoot,
+                              start,
+                              dump_limit,
+                              total_count,
+                              retainers_arr,
+                              &count,
+                              &index,
+                              "<root>",
+                              id_sym,
+                              desc_sym,
+                              size_sym,
+                              error)) {
+    return -1;
+  }
+
+  lol_visitor.reset();
+  Heap::IterateWeakRoots(&lol_visitor, VISIT_ALL);
+  if (!AddRootRetainerIfFound(lol_visitor,
+                              filter,
+                              summary,
+                              SetFoundWeakRoot,
+                              start,
+                              dump_limit,
+                              total_count,
+                              retainers_arr,
+                              &count,
+                              &index,
+                              "<weak root>",
+                              id_sym,
+                              desc_sym,
+                              size_sym,
+                              error)) {
+    return -1;
+  }
+
+  // Iterate the live object lists.
+  LolIterator it(NULL, last());
+  for (it.Init(); !it.Done() && (index < dump_limit); it.Next()) {
+    HeapObject* heap_obj = it.Obj();
+
+    // Only look at all JSObjects.
+    if (heap_obj->IsJSObject()) {
+      // Skip context extension objects and argument arrays as these are
+      // checked in the context of functions using them.
+      JSObject* obj = JSObject::cast(heap_obj);
+      if (obj->IsJSContextExtensionObject() ||
+          obj->map()->constructor() == arguments_function) {
+        continue;
+      }
+
+      // Check if the JS object has a reference to the object looked for.
+      if (obj->ReferencesObject(*target)) {
+        // Check instance filter if supplied. This is normally used to avoid
+        // references from mirror objects (see Runtime_IsInPrototypeChain).
+        if (!instance_filter->IsUndefined()) {
+          Object* V = obj;
+          while (true) {
+            Object* prototype = V->GetPrototype();
+            if (prototype->IsNull()) {
+              break;
+            }
+            if (*instance_filter == prototype) {
+              obj = NULL;  // Don't add this object.
+              break;
+            }
+            V = prototype;
+          }
+        }
+
+        if (obj != NULL) {
+          // Skip objects that have been filtered out.
+          if (filter->Matches(heap_obj)) {
+            continue;
+          }
+
+          // Valid reference found add to instance array if supplied an update
+          // count.
+          last_obj = Handle<JSObject>(obj);
+          (*total_count)++;
+
+          if (summary != NULL) {
+            summary->Add(heap_obj);
+          } else if ((*total_count > start) && (index < dump_limit)) {
+            count++;
+            if (!retainers_arr.is_null()) {
+              retainer = Handle<HeapObject>(heap_obj);
+              bool success = AddObjDetail(retainers_arr,
+                                          index++,
+                                          it.Id(),
+                                          retainer,
+                                          NULL,
+                                          id_sym,
+                                          desc_sym,
+                                          size_sym,
+                                          detail,
+                                          desc,
+                                          error);
+              if (!success) return -1;
+            }
+          }
+        }
+      }
+    }
+  }
+
+  // Check for circular reference only. This can happen when the object is only
+  // referenced from mirrors and has a circular reference in which case the
+  // object is not really alive and would have been garbage collected if not
+  // referenced from the mirror.
+
+  if (*total_count == 1 && !last_obj.is_null() && *last_obj == *target) {
+    count = 0;
+    *total_count = 0;
+  }
+
+  return count;
+}
+
+
+MaybeObject* LiveObjectList::GetObjRetainers(int obj_id,
+                                             Handle<JSObject> instance_filter,
+                                             bool verbose,
+                                             int start,
+                                             int dump_limit,
+                                             Handle<JSObject> filter_obj) {
+  HandleScope scope;
+
+  // Get the target object.
+  HeapObject* heap_obj = HeapObject::cast(GetObj(obj_id));
+  if (heap_obj == Heap::undefined_value()) {
+    return heap_obj;
+  }
+
+  Handle<HeapObject> target = Handle<HeapObject>(heap_obj);
+
+  // Get the constructor function for context extension and arguments array.
+  JSObject* arguments_boilerplate =
+      Top::context()->global_context()->arguments_boilerplate();
+  JSFunction* arguments_function =
+      JSFunction::cast(arguments_boilerplate->map()->constructor());
+
+  Handle<JSFunction> args_function = Handle<JSFunction>(arguments_function);
+  LolFilter filter(filter_obj);
+
+  if (!verbose) {
+    RetainersSummaryWriter writer(target, instance_filter, args_function);
+    return SummarizePrivate(&writer, &filter, true);
+
+  } else {
+    RetainersDumpWriter writer(target, instance_filter, args_function);
+    Object* body_obj;
+    MaybeObject* maybe_result =
+        DumpPrivate(&writer, start, dump_limit, &filter);
+    if (!maybe_result->ToObject(&body_obj)) {
+      return maybe_result;
+    }
+
+    // Set body.id.
+    Handle<JSObject> body = Handle<JSObject>(JSObject::cast(body_obj));
+    Handle<String> id_sym = Factory::LookupAsciiSymbol("id");
+    maybe_result = body->SetProperty(*id_sym,
+                                     Smi::FromInt(obj_id),
+                                     NONE,
+                                     kNonStrictMode);
+    if (maybe_result->IsFailure()) return maybe_result;
+
+    return *body;
+  }
+}
+
+
+Object* LiveObjectList::PrintObj(int obj_id) {
+  Object* obj = GetObj(obj_id);
+  if (!obj) {
+    return Heap::undefined_value();
+  }
+
+  EmbeddedVector<char, 128> temp_filename;
+  static int temp_count = 0;
+  const char* path_prefix = ".";
+
+  if (FLAG_lol_workdir) {
+    path_prefix = FLAG_lol_workdir;
+  }
+  OS::SNPrintF(temp_filename, "%s/lol-print-%d", path_prefix, ++temp_count);
+
+  FILE* f = OS::FOpen(temp_filename.start(), "w+");
+
+  PrintF(f, "@%d ", LiveObjectList::GetObjId(obj));
+#ifdef OBJECT_PRINT
+#ifdef INSPECTOR
+  Inspector::DumpObjectType(f, obj);
+#endif  // INSPECTOR
+  PrintF(f, "\n");
+  obj->Print(f);
+#else  // !OBJECT_PRINT
+  obj->ShortPrint(f);
+#endif  // !OBJECT_PRINT
+  PrintF(f, "\n");
+  Flush(f);
+  fclose(f);
+
+  // Create a string from the temp_file.
+  // Note: the mmapped resource will take care of closing the file.
+  MemoryMappedExternalResource* resource =
+      new MemoryMappedExternalResource(temp_filename.start(), true);
+  if (resource->exists() && !resource->is_empty()) {
+    ASSERT(resource->IsAscii());
+    Handle<String> dump_string =
+        Factory::NewExternalStringFromAscii(resource);
+    ExternalStringTable::AddString(*dump_string);
+    return *dump_string;
+  } else {
+    delete resource;
+  }
+  return Heap::undefined_value();
+}
+
+
+class LolPathTracer: public PathTracer {
+ public:
+  LolPathTracer(FILE* out,
+                Object* search_target,
+                WhatToFind what_to_find)
+      : PathTracer(search_target, what_to_find, VISIT_ONLY_STRONG), out_(out) {}
+
+ private:
+  void ProcessResults();
+
+  FILE* out_;
+};
+
+
+void LolPathTracer::ProcessResults() {
+  if (found_target_) {
+    PrintF(out_, "=====================================\n");
+    PrintF(out_, "====        Path to object       ====\n");
+    PrintF(out_, "=====================================\n\n");
+
+    ASSERT(!object_stack_.is_empty());
+    Object* prev = NULL;
+    for (int i = 0, index = 0; i < object_stack_.length(); i++) {
+      Object* obj = object_stack_[i];
+
+      // Skip this object if it is basically the internals of the
+      // previous object (which would have dumped its details already).
+      if (prev && prev->IsJSObject() &&
+          (obj != search_target_)) {
+        JSObject* jsobj = JSObject::cast(prev);
+        if (obj->IsFixedArray() &&
+            jsobj->properties() == FixedArray::cast(obj)) {
+          // Skip this one because it would have been printed as the
+          // properties of the last object already.
+          continue;
+        } else if (obj->IsHeapObject() &&
+                   jsobj->elements() == HeapObject::cast(obj)) {
+          // Skip this one because it would have been printed as the
+          // elements of the last object already.
+          continue;
+        }
+      }
+
+      // Print a connecting arrow.
+      if (i > 0) PrintF(out_, "\n     |\n     |\n     V\n\n");
+
+      // Print the object index.
+      PrintF(out_, "[%d] ", ++index);
+
+      // Print the LOL object ID:
+      int id = LiveObjectList::GetObjId(obj);
+      if (id > 0) PrintF(out_, "@%d ", id);
+
+#ifdef OBJECT_PRINT
+#ifdef INSPECTOR
+      Inspector::DumpObjectType(out_, obj);
+#endif  // INSPECTOR
+      PrintF(out_, "\n");
+      obj->Print(out_);
+#else  // !OBJECT_PRINT
+      obj->ShortPrint(out_);
+      PrintF(out_, "\n");
+#endif  // !OBJECT_PRINT
+      Flush(out_);
+    }
+    PrintF(out_, "\n");
+    PrintF(out_, "=====================================\n\n");
+    Flush(out_);
+  }
+}
+
+
+Object* LiveObjectList::GetPathPrivate(HeapObject* obj1, HeapObject* obj2) {
+  EmbeddedVector<char, 128> temp_filename;
+  static int temp_count = 0;
+  const char* path_prefix = ".";
+
+  if (FLAG_lol_workdir) {
+    path_prefix = FLAG_lol_workdir;
+  }
+  OS::SNPrintF(temp_filename, "%s/lol-getpath-%d", path_prefix, ++temp_count);
+
+  FILE* f = OS::FOpen(temp_filename.start(), "w+");
+
+  // Save the previous verbosity.
+  bool prev_verbosity = FLAG_use_verbose_printer;
+  FLAG_use_verbose_printer = false;
+
+  // Dump the paths.
+  {
+    // The tracer needs to be scoped because its usage asserts no allocation,
+    // and we need to allocate the result string below.
+    LolPathTracer tracer(f, obj2, LolPathTracer::FIND_FIRST);
+
+    bool found = false;
+    if (obj1 == NULL) {
+      // Check for ObjectGroups that references this object.
+      // TODO(mlam): refactor this to be more modular.
+      {
+        List<ObjectGroup*>* groups = GlobalHandles::ObjectGroups();
+        for (int i = 0; i < groups->length(); i++) {
+          ObjectGroup* group = groups->at(i);
+          if (group == NULL) continue;
+
+          bool found_group = false;
+          List<Object**>& objects = group->objects_;
+          for (int j = 0; j < objects.length(); j++) {
+            Object* object = *objects[j];
+            HeapObject* hobj = HeapObject::cast(object);
+            if (obj2 == hobj) {
+              found_group = true;
+              break;
+            }
+          }
+
+          if (found_group) {
+            PrintF(f,
+                   "obj %p is a member of object group %p {\n",
+                   reinterpret_cast<void*>(obj2),
+                   reinterpret_cast<void*>(group));
+            for (int j = 0; j < objects.length(); j++) {
+              Object* object = *objects[j];
+              if (!object->IsHeapObject()) continue;
+
+              HeapObject* hobj = HeapObject::cast(object);
+              int id = GetObjId(hobj);
+              if (id != 0) {
+                PrintF(f, "  @%d:", id);
+              } else {
+                PrintF(f, "  <no id>:");
+              }
+
+              char buffer[512];
+              GenerateObjectDesc(hobj, buffer, sizeof(buffer));
+              PrintF(f, " %s", buffer);
+              if (hobj == obj2) {
+                PrintF(f, " <===");
+              }
+              PrintF(f, "\n");
+            }
+            PrintF(f, "}\n");
+          }
+        }
+      }
+
+      PrintF(f, "path from roots to obj %p\n", reinterpret_cast<void*>(obj2));
+      Heap::IterateRoots(&tracer, VISIT_ONLY_STRONG);
+      found = tracer.found();
+
+      if (!found) {
+        PrintF(f, "  No paths found. Checking symbol tables ...\n");
+        SymbolTable* symbol_table = Heap::raw_unchecked_symbol_table();
+        tracer.VisitPointers(reinterpret_cast<Object**>(&symbol_table),
+                             reinterpret_cast<Object**>(&symbol_table)+1);
+        found = tracer.found();
+        if (!found) {
+          symbol_table->IteratePrefix(&tracer);
+          found = tracer.found();
+        }
+      }
+
+      if (!found) {
+        PrintF(f, "  No paths found. Checking weak roots ...\n");
+        // Check weak refs next.
+        GlobalHandles::IterateWeakRoots(&tracer);
+        found = tracer.found();
+      }
+
+    } else {
+      PrintF(f, "path from obj %p to obj %p:\n",
+             reinterpret_cast<void*>(obj1), reinterpret_cast<void*>(obj2));
+      tracer.TracePathFrom(reinterpret_cast<Object**>(&obj1));
+      found = tracer.found();
+    }
+
+    if (!found) {
+      PrintF(f, "  No paths found\n\n");
+    }
+  }
+
+  // Flush and clean up the dumped file.
+  Flush(f);
+  fclose(f);
+
+  // Restore the previous verbosity.
+  FLAG_use_verbose_printer = prev_verbosity;
+
+  // Create a string from the temp_file.
+  // Note: the mmapped resource will take care of closing the file.
+  MemoryMappedExternalResource* resource =
+      new MemoryMappedExternalResource(temp_filename.start(), true);
+  if (resource->exists() && !resource->is_empty()) {
+    ASSERT(resource->IsAscii());
+    Handle<String> path_string =
+        Factory::NewExternalStringFromAscii(resource);
+    ExternalStringTable::AddString(*path_string);
+    return *path_string;
+  } else {
+    delete resource;
+  }
+  return Heap::undefined_value();
+}
+
+
+Object* LiveObjectList::GetPath(int obj_id1,
+                                int obj_id2,
+                                Handle<JSObject> instance_filter) {
+  HandleScope scope;
+
+  // Get the target object.
+  HeapObject* obj1 = NULL;
+  if (obj_id1 != 0) {
+    obj1 = HeapObject::cast(GetObj(obj_id1));
+    if (obj1 == Heap::undefined_value()) {
+      return obj1;
+    }
+  }
+
+  HeapObject* obj2 = HeapObject::cast(GetObj(obj_id2));
+  if (obj2 == Heap::undefined_value()) {
+    return obj2;
+  }
+
+  return GetPathPrivate(obj1, obj2);
+}
+
+
+void LiveObjectList::DoProcessNonLive(HeapObject *obj) {
+  // We should only be called if we have at least one lol to search.
+  ASSERT(last() != NULL);
+  Element* element = last()->Find(obj);
+  if (element != NULL) {
+    NullifyNonLivePointer(&element->obj_);
+  }
+}
+
+
+void LiveObjectList::IterateElementsPrivate(ObjectVisitor* v) {
+  LiveObjectList* lol = last();
+  while (lol != NULL) {
+    Element* elements = lol->elements_;
+    int count = lol->obj_count_;
+    for (int i = 0; i < count; i++) {
+      HeapObject** p = &elements[i].obj_;
+      v->VisitPointer(reinterpret_cast<Object **>(p));
+    }
+    lol = lol->prev_;
+  }
+}
+
+
+// Purpose: Called by GCEpilogue to purge duplicates.  Not to be called by
+// anyone else.
+void LiveObjectList::PurgeDuplicates() {
+  bool is_sorted = false;
+  LiveObjectList* lol = last();
+  if (!lol) {
+    return;  // Nothing to purge.
+  }
+
+  int total_count = lol->TotalObjCount();
+  if (!total_count) {
+    return;  // Nothing to purge.
+  }
+
+  Element* elements = NewArray<Element>(total_count);
+  int count = 0;
+
+  // Copy all the object elements into a consecutive array.
+  while (lol) {
+    memcpy(&elements[count], lol->elements_, lol->obj_count_ * sizeof(Element));
+    count += lol->obj_count_;
+    lol = lol->prev_;
+  }
+  qsort(elements, total_count, sizeof(Element),
+        reinterpret_cast<RawComparer>(CompareElement));
+
+  ASSERT(count == total_count);
+
+  // Iterate over all objects in the consolidated list and check for dups.
+  total_count--;
+  for (int i = 0; i < total_count; ) {
+    Element* curr = &elements[i];
+    HeapObject* curr_obj = curr->obj_;
+    int j = i+1;
+    bool done = false;
+
+    while (!done && (j < total_count)) {
+      // Process if the element's object is still live after the current GC.
+      // Non-live objects will be converted to SMIs i.e. not HeapObjects.
+      if (curr_obj->IsHeapObject()) {
+        Element* next = &elements[j];
+        HeapObject* next_obj = next->obj_;
+        if (next_obj->IsHeapObject()) {
+          if (curr_obj != next_obj) {
+            done = true;
+            continue;  // Live object but no match.  Move on.
+          }
+
+          // NOTE: we've just GCed the LOLs.  Hence, they are no longer sorted.
+          // Since we detected at least one need to search for entries, we'll
+          // sort it to enable the use of NullifyMostRecent() below.  We only
+          // need to sort it once (except for one exception ... see below).
+          if (!is_sorted) {
+            SortAll();
+            is_sorted = true;
+          }
+
+          // We have a match.  Need to nullify the most recent ref to this
+          // object.  We'll keep the oldest ref:
+          // Note: we will nullify the element record in the LOL
+          // database, not in the local sorted copy of the elements.
+          NullifyMostRecent(curr_obj);
+        }
+      }
+      // Either the object was already marked for purging, or we just marked
+      // it.  Either way, if there's more than one dup, then we need to check
+      // the next element for another possible dup against the current as well
+      // before we move on.  So, here we go.
+      j++;
+    }
+
+    // We can move on to checking the match on the next element.
+    i = j;
+  }
+
+  DeleteArray<Element>(elements);
+}
+
+
+// Purpose: Purges dead objects and resorts the LOLs.
+void LiveObjectList::GCEpiloguePrivate() {
+  // Note: During the GC, ConsStrings may be collected and pointers may be
+  // forwarded to its constituent string.  As a result, we may find dupes of
+  // objects references in the LOL list.
+  // Another common way we get dups is that free chunks that have been swept
+  // in the oldGen heap may be kept as ByteArray objects in a free list.
+  //
+  // When we promote live objects from the youngGen, the object may be moved
+  // to the start of these free chunks.  Since there is no free or move event
+  // for the free chunks, their addresses will show up 2 times: once for their
+  // original free ByteArray selves, and once for the newly promoted youngGen
+  // object.  Hence, we can get a duplicate address in the LOL again.
+  //
+  // We need to eliminate these dups because the LOL implementation expects to
+  // only have at most one unique LOL reference to any object at any time.
+  PurgeDuplicates();
+
+  // After the GC, sweep away all free'd Elements and compact.
+  LiveObjectList *prev = NULL;
+  LiveObjectList *next = NULL;
+
+  // Iterating from the youngest lol to the oldest lol.
+  for (LiveObjectList *lol = last(); lol; lol = prev) {
+    Element* elements = lol->elements_;
+    prev = lol->prev();  // Save the prev.
+
+    // Remove any references to collected objects.
+    int i = 0;
+    while (i < lol->obj_count_) {
+      Element& element = elements[i];
+      if (!element.obj_->IsHeapObject()) {
+        // If the HeapObject address was converted into a SMI, then this
+        // is a dead object.  Copy the last element over this one.
+        element = elements[lol->obj_count_ - 1];
+        lol->obj_count_--;
+        // We've just moved the last element into this index.  We'll revisit
+        // this index again.  Hence, no need to increment the iterator.
+      } else {
+        i++;  // Look at the next element next.
+      }
+    }
+
+    int new_count = lol->obj_count_;
+
+    // Check if there are any more elements to keep after purging the dead ones.
+    if (new_count == 0) {
+      DeleteArray<Element>(elements);
+      lol->elements_ = NULL;
+      lol->capacity_ = 0;
+      ASSERT(lol->obj_count_ == 0);
+
+      // If the list is also invisible, the clean up the list as well.
+      if (lol->id_ == 0) {
+        // Point the next lol's prev to this lol's prev.
+        if (next) {
+          next->prev_ = lol->prev_;
+        } else {
+          last_ = lol->prev_;
+        }
+
+        // Delete this now empty and invisible lol.
+        delete lol;
+
+        // Don't point the next to this lol since it is now deleted.
+        // Leave the next pointer pointing to the current lol.
+        continue;
+      }
+
+    } else {
+      // If the obj_count_ is less than the capacity and the difference is
+      // greater than a specified threshold, then we should shrink the list.
+      int diff = lol->capacity_ - new_count;
+      const int kMaxUnusedSpace = 64;
+      if (diff > kMaxUnusedSpace) {  // Threshold for shrinking.
+        // Shrink the list.
+        Element *new_elements = NewArray<Element>(new_count);
+        memcpy(new_elements, elements, new_count * sizeof(Element));
+
+        DeleteArray<Element>(elements);
+        lol->elements_ = new_elements;
+        lol->capacity_ = new_count;
+      }
+      ASSERT(lol->obj_count_ == new_count);
+
+      lol->Sort();  // We've moved objects.  Re-sort in case.
+    }
+
+    // Save the next (for the previous link) in case we need it later.
+    next = lol;
+  }
+
+#ifdef VERIFY_LOL
+  if (FLAG_verify_lol) {
+    Verify();
+  }
+#endif
+}
+
+
+#ifdef VERIFY_LOL
+void LiveObjectList::Verify(bool match_heap_exactly) {
+  OS::Print("Verifying the LiveObjectList database:\n");
+
+  LiveObjectList* lol = last();
+  if (lol == NULL) {
+    OS::Print("  No lol database to verify\n");
+    return;
+  }
+
+  OS::Print("  Preparing the lol database ...\n");
+  int total_count = lol->TotalObjCount();
+
+  Element* elements = NewArray<Element>(total_count);
+  int count = 0;
+
+  // Copy all the object elements into a consecutive array.
+  OS::Print("  Copying the lol database ...\n");
+  while (lol != NULL) {
+    memcpy(&elements[count], lol->elements_, lol->obj_count_ * sizeof(Element));
+    count += lol->obj_count_;
+    lol = lol->prev_;
+  }
+  qsort(elements, total_count, sizeof(Element),
+        reinterpret_cast<RawComparer>(CompareElement));
+
+  ASSERT(count == total_count);
+
+  // Iterate over all objects in the heap and check for:
+  // 1. object in LOL but not in heap i.e. error.
+  // 2. object in heap but not in LOL (possibly not an error).  Usually
+  //    just means that we don't have the a capture of the latest heap.
+  //    That is unless we did this verify immediately after a capture,
+  //    and specified match_heap_exactly = true.
+
+  int number_of_heap_objects = 0;
+  int number_of_matches = 0;
+  int number_not_in_heap = total_count;
+  int number_not_in_lol = 0;
+
+  OS::Print("  Start verify ...\n");
+  OS::Print("  Verifying ...");
+  Flush();
+  HeapIterator iterator(HeapIterator::kFilterFreeListNodes);
+  HeapObject* heap_obj = NULL;
+  while ((heap_obj = iterator.next()) != NULL) {
+    number_of_heap_objects++;
+
+    // Check if the heap_obj is in the lol.
+    Element key;
+    key.obj_ = heap_obj;
+
+    Element* result = reinterpret_cast<Element*>(
+        bsearch(&key, elements, total_count, sizeof(Element),
+                reinterpret_cast<RawComparer>(CompareElement)));
+
+    if (result != NULL) {
+      number_of_matches++;
+      number_not_in_heap--;
+      // Mark it as found by changing it into a SMI (mask off low bit).
+      // Note: we cannot use HeapObject::cast() here because it asserts that
+      // the HeapObject bit is set on the address, but we're unsetting it on
+      // purpose here for our marking.
+      result->obj_ = reinterpret_cast<HeapObject*>(heap_obj->address());
+
+    } else {
+      number_not_in_lol++;
+      if (match_heap_exactly) {
+        OS::Print("heap object %p NOT in lol database\n", heap_obj);
+      }
+    }
+    // Show some sign of life.
+    if (number_of_heap_objects % 1000 == 0) {
+      OS::Print(".");
+      fflush(stdout);
+    }
+  }
+  OS::Print("\n");
+
+  // Reporting lol objects not found in the heap.
+  if (number_not_in_heap) {
+    int found = 0;
+    for (int i = 0; (i < total_count) && (found < number_not_in_heap); i++) {
+      Element& element = elements[i];
+      if (element.obj_->IsHeapObject()) {
+        OS::Print("lol database object [%d of %d] %p NOT in heap\n",
+                  i, total_count, element.obj_);
+        found++;
+      }
+    }
+  }
+
+  DeleteArray<Element>(elements);
+
+  OS::Print("number of objects in lol database %d\n", total_count);
+  OS::Print("number of heap objects .......... %d\n", number_of_heap_objects);
+  OS::Print("number of matches ............... %d\n", number_of_matches);
+  OS::Print("number NOT in heap .............. %d\n", number_not_in_heap);
+  OS::Print("number NOT in lol database ...... %d\n", number_not_in_lol);
+
+  if (number_of_matches != total_count) {
+    OS::Print("  *** ERROR: "
+              "NOT all lol database objects match heap objects.\n");
+  }
+  if (number_not_in_heap != 0) {
+    OS::Print("  *** ERROR: %d lol database objects not found in heap.\n",
+              number_not_in_heap);
+  }
+  if (match_heap_exactly) {
+    if (!(number_not_in_lol == 0)) {
+      OS::Print("  *** ERROR: %d heap objects NOT found in lol database.\n",
+                number_not_in_lol);
+    }
+  }
+
+  ASSERT(number_of_matches == total_count);
+  ASSERT(number_not_in_heap == 0);
+  ASSERT(number_not_in_lol == (number_of_heap_objects - total_count));
+  if (match_heap_exactly) {
+    ASSERT(total_count == number_of_heap_objects);
+    ASSERT(number_not_in_lol == 0);
+  }
+
+  OS::Print("  Verify the lol database is sorted ...\n");
+  lol = last();
+  while (lol != NULL) {
+    Element* elements = lol->elements_;
+    for (int i = 0; i < lol->obj_count_ - 1; i++) {
+      if (elements[i].obj_ >= elements[i+1].obj_) {
+        OS::Print("  *** ERROR: lol %p obj[%d] %p > obj[%d] %p\n",
+                  lol, i, elements[i].obj_, i+1, elements[i+1].obj_);
+      }
+    }
+    lol = lol->prev_;
+  }
+
+  OS::Print("  DONE verifying.\n\n\n");
+}
+
+
+void LiveObjectList::VerifyNotInFromSpace() {
+  OS::Print("VerifyNotInFromSpace() ...\n");
+  LolIterator it(NULL, last());
+  int i = 0;
+  for (it.Init(); !it.Done(); it.Next()) {
+    HeapObject* heap_obj = it.Obj();
+    if (Heap::InFromSpace(heap_obj)) {
+      OS::Print(" ERROR: VerifyNotInFromSpace: [%d] obj %p in From space %p\n",
+                i++, heap_obj, Heap::new_space()->FromSpaceLow());
+    }
+  }
+}
+#endif  // VERIFY_LOL
+
 
 } }  // namespace v8::internal
 
 #endif  // LIVE_OBJECT_LIST