Track JS allocations as they arrive with no affection on performance when tracking is switched off

src/heap-snapshot-generator.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 379 matching lines @@
   // This fact is using in MoveObject method.
   entries_.Add(EntryInfo(0, NULL, 0));
 }
 
 
 void HeapObjectsMap::SnapshotGenerationFinished() {
   RemoveDeadEntries();
 }
 
 
-void HeapObjectsMap::MoveObject(Address from, Address to) {
+void HeapObjectsMap::MoveObject(Address from, Address to, int object_size) {
   ASSERT(to != NULL);
   ASSERT(from != NULL);
   if (from == to) return;
   void* from_value = entries_map_.Remove(from, ComputePointerHash(from));
   if (from_value == NULL) {
     // It may occur that some untracked object moves to an address X and there
     // is a tracked object at that address. In this case we should remove the
     // entry as we know that the object has died.
     void* to_value = entries_map_.Remove(to, ComputePointerHash(to));
     if (to_value != NULL) {
@@ skipping 10 matching lines @@
       // value in addr field. It is bad because later at RemoveDeadEntries
       // one of this entry will be removed with the corresponding entries_map_
       // entry.
       int to_entry_info_index =
           static_cast<int>(reinterpret_cast<intptr_t>(to_entry->value));
       entries_.at(to_entry_info_index).addr = NULL;
     }
     int from_entry_info_index =
         static_cast<int>(reinterpret_cast<intptr_t>(from_value));
     entries_.at(from_entry_info_index).addr = to;
+    // Size of an object can change during its life, so to keep information
+    // about the object in entries_ consistent, we have to adjust size when the
+    // object is migrated.
+    entries_.at(from_entry_info_index).size = object_size;
     to_entry->value = from_value;
   }
 }
 
 
+void HeapObjectsMap::NewObject(Address addr, int size) {
+  ASSERT(addr != NULL);
+  FindOrAddEntry(addr, size, false);
+}
+
+
+void HeapObjectsMap::UpdateObjectSize(Address addr, int size) {
+  FindOrAddEntry(addr, size, false);

[Hannes Payer (out of office), 2013/10/02 18:00:29]

Why do we have two implementations of the same functions?

[Alexandra Mikhaylova, 2013/10/03 16:27:55]

Sometimes we want just to update the information (the size) of the object that
has already been tracked. This works pretty much the same as reqistering a new
object, but one more call of NewObjectEvent (and NewObject) can confuse other
developers, so we decided to create separate methods for it.

For example, here
https://codereview.chromium.org/22852024/diff/84001/src/heap.cc both an object
and its allocation memento are allocated in one go. So then we track the
allocation memento as a new object and adjust information about the size of the
original object itself.

[Hannes Payer (out of office), 2013/10/10 18:54:40]

Since both functions implement the same functionality, it should really be just
one function. Let's find a more abstract name for the function. We could call it
CreateOrUpdateObjectSize which would be similar to FindOrAddEntry...

+}
+
+
 SnapshotObjectId HeapObjectsMap::FindEntry(Address addr) {
   HashMap::Entry* entry = entries_map_.Lookup(addr, ComputePointerHash(addr),
                                               false);
   if (entry == NULL) return 0;
   int entry_index = static_cast<int>(reinterpret_cast<intptr_t>(entry->value));
   EntryInfo& entry_info = entries_.at(entry_index);
   ASSERT(static_cast<uint32_t>(entries_.length()) > entries_map_.occupancy());
   return entry_info.id;
 }
 
 
 SnapshotObjectId HeapObjectsMap::FindOrAddEntry(Address addr,
-                                                unsigned int size) {
+                                                unsigned int size,
+                                                bool accessed) {
   ASSERT(static_cast<uint32_t>(entries_.length()) > entries_map_.occupancy());
   HashMap::Entry* entry = entries_map_.Lookup(addr, ComputePointerHash(addr),
                                               true);
   if (entry->value != NULL) {
     int entry_index =
         static_cast<int>(reinterpret_cast<intptr_t>(entry->value));
     EntryInfo& entry_info = entries_.at(entry_index);
-    entry_info.accessed = true;
+    entry_info.accessed = accessed;
     entry_info.size = size;
     return entry_info.id;
   }
   entry->value = reinterpret_cast<void*>(entries_.length());
   SnapshotObjectId id = next_id_;
   next_id_ += kObjectIdStep;
-  entries_.Add(EntryInfo(id, addr, size));
+  entries_.Add(EntryInfo(id, addr, size, accessed));
   ASSERT(static_cast<uint32_t>(entries_.length()) > entries_map_.occupancy());
   return id;
 }
 
 
 void HeapObjectsMap::StopHeapObjectsTracking() {
   time_intervals_.Clear();
 }
 
 
 void HeapObjectsMap::UpdateHeapObjectsMap() {
   heap_->CollectAllGarbage(Heap::kMakeHeapIterableMask,
                           "HeapSnapshotsCollection::UpdateHeapObjectsMap");
   HeapIterator iterator(heap_);
   for (HeapObject* obj = iterator.next();
        obj != NULL;
        obj = iterator.next()) {
     FindOrAddEntry(obj->address(), obj->Size());
   }
   RemoveDeadEntries();
 }
 
 
+int HeapObjectsMap::FindUntrackedObjects() {
+  HeapIterator iterator(heap_);
+  int untracked = 0;
+  for (HeapObject* obj = iterator.next();
+       obj != NULL;
+       obj = iterator.next()) {
+    HashMap::Entry* entry = entries_map_.Lookup(
+      obj->address(), ComputePointerHash(obj->address()), false);
+    if (entry == NULL) {
+      untracked++;
+    } else {
+      int entry_index = static_cast<int>(
+          reinterpret_cast<intptr_t>(entry->value));
+      EntryInfo& entry_info = entries_.at(entry_index);
+      CHECK_EQ(obj->Size(), static_cast<int>(entry_info.size));
+    }
+  }
+  return untracked;
+}
+
+
 SnapshotObjectId HeapObjectsMap::PushHeapObjectsStats(OutputStream* stream) {
   UpdateHeapObjectsMap();
   time_intervals_.Add(TimeInterval(next_id_));
   int prefered_chunk_size = stream->GetChunkSize();
   List<v8::HeapStatsUpdate> stats_buffer;
   ASSERT(!entries_.is_empty());
   EntryInfo* entry_info = &entries_.first();
   EntryInfo* end_entry_info = &entries_.last() + 1;
   for (int time_interval_index = 0;
        time_interval_index < time_intervals_.length();
@@ skipping 2209 matching lines @@
   writer_->AddString("\"<dummy>\"");
   for (int i = 1; i < sorted_strings.length(); ++i) {
     writer_->AddCharacter(',');
     SerializeString(sorted_strings[i]);
     if (writer_->aborted()) return;
   }
 }
 
 
 } }  // namespace v8::internal