[WIP] New GC related APIs.

src/global-handles.cc

Index: src/global-handles.cc
diff --git a/src/global-handles.cc b/src/global-handles.cc
index cb3115abfca7db7ce9baec4a29c9da134437c223..1201f32aa851fa53bf06c8881c377866f2a9e545 100644
--- a/src/global-handles.cc
+++ b/src/global-handles.cc
@@ -37,7 +37,11 @@ namespace internal {
 
 
 ObjectGroup::~ObjectGroup() {
-  if (info_ != NULL) info_->Dispose();
+  if (info != NULL) info->Dispose();
+}
+
+
+GroupRetainedObjectInfo::~GroupRetainedObjectInfo() {
 }
 
 
@@ -438,7 +442,8 @@ GlobalHandles::GlobalHandles(Isolate* isolate)
       first_block_(NULL),
       first_used_block_(NULL),
       first_free_(NULL),
-      post_gc_processing_count_(0) {}
+      post_gc_processing_count_(0),
+      object_groups_(new List<ObjectGroupConnection>()) {}
 
 
 GlobalHandles::~GlobalHandles() {
@@ -449,6 +454,7 @@ GlobalHandles::~GlobalHandles() {
     block = tmp;
   }
   first_block_ = NULL;
+  delete object_groups_;
 }
 
 
@@ -575,48 +581,58 @@ void GlobalHandles::IterateNewSpaceWeakIndependentRoots(ObjectVisitor* v) {
   }
 }
 
-
 bool GlobalHandles::IterateObjectGroups(ObjectVisitor* v,
                                         WeakSlotCallbackWithHeap can_skip) {
-  int last = 0;
+  if (object_groups_->length() == 0)
+    return false;
+
+  object_groups_->Sort();
+  // Stores information about unvisited object groups for later use.
+  List<ObjectGroupConnection>* new_object_groups =
+      new List<ObjectGroupConnection>();
+
+  void* current_group_id = NULL;
+  size_t current_group_start = 0;
   bool any_group_was_visited = false;
-  for (int i = 0; i < object_groups_.length(); i++) {
-    ObjectGroup* entry = object_groups_.at(i);
-    ASSERT(entry != NULL);
-
-    Object*** objects = entry->objects_;
-    bool group_should_be_visited = false;
-    for (size_t j = 0; j < entry->length_; j++) {
-      Object* object = *objects[j];
-      if (object->IsHeapObject()) {
-        if (!can_skip(isolate_->heap(), &object)) {
-          group_should_be_visited = true;
-          break;
+
+  for (int i = 0; i <= object_groups_->length(); ++i) {
+    if (i == 0)
+      current_group_id = object_groups_->at(i).id;
+    if (i == object_groups_->length() ||
+        current_group_id != object_groups_->at(i).id) {
+      // Group detected: objects in indices [current_group_start, i[.
+      bool group_should_be_visited = false;
+      for (int j = current_group_start; j < i; ++j) {
+        Object* object = *(object_groups_->at(j).object);
+        if (object->IsHeapObject()) {
+          if (!can_skip(isolate_->heap(), &object)) {
+            group_should_be_visited = true;
+            break;
+          }
         }
       }
-    }
-
-    if (!group_should_be_visited) {
-      object_groups_[last++] = entry;
-      continue;
-    }
-
-    // An object in the group requires visiting, so iterate over all
-    // objects in the group.
-    for (size_t j = 0; j < entry->length_; ++j) {
-      Object* object = *objects[j];
-      if (object->IsHeapObject()) {
-        v->VisitPointer(&object);
-        any_group_was_visited = true;
+      if (!group_should_be_visited) {
+        for (int j = current_group_start; j < i; ++j)
+          new_object_groups->Add(object_groups_->at(j));

[Michael Starzinger, 2013/04/09 14:18:40]

It would be good if we could get by with an in-place version of this function as
before which doesn't require to copy into a new-list.

[marja, 2013/04/09 16:46:51]

Done.

+      } else {
+        // An object in the group requires visiting, so iterate over all
+        // objects in the group.
+        for (int j = current_group_start; j < i; ++j) {
+          Object* object = *(object_groups_->at(j).object);
+          if (object->IsHeapObject()) {
+            v->VisitPointer(&object);
+            any_group_was_visited = true;
+          }
+        }
+      }
+      if (i < object_groups_->length()) {
+        current_group_id = object_groups_->at(i).id;
+        current_group_start = i;
       }
     }
-
-    // Once the entire group has been iterated over, set the object
-    // group to NULL so it won't be processed again.
-    entry->Dispose();
-    object_groups_.at(i) = NULL;
   }
-  object_groups_.Rewind(last);
+  delete object_groups_;
+  object_groups_ = new_object_groups;
   return any_group_was_visited;
 }
 
@@ -824,7 +840,21 @@ void GlobalHandles::AddObjectGroup(Object*** handles,
     if (info != NULL) info->Dispose();
     return;
   }
-  object_groups_.Add(ObjectGroup::New(handles, length, info));
+  for (size_t i = 0; i < length; ++i)
+    object_groups_->Add(ObjectGroupConnection(handles[0], handles[i]));
+  retained_object_infos_.Add(GroupRetainedObjectInfo(handles[0], info));
+}
+
+
+void GlobalHandles::SetObjectGroupId(Object** handle,
+                                     void* id) {
+  object_groups_->Add(ObjectGroupConnection(id, handle));
+}
+
+
+void GlobalHandles::SetRetainedObjectInfo(void* id,
+                                          RetainedObjectInfo* info) {
+  retained_object_infos_.Add(GroupRetainedObjectInfo(id, info));
 }
 
 
@@ -841,12 +871,50 @@ void GlobalHandles::AddImplicitReferences(HeapObject** parent,
   implicit_ref_groups_.Add(ImplicitRefGroup::New(parent, children, length));
 }
 
+List<ObjectGroup*>* GlobalHandles::object_groups() {

[Michael Starzinger, 2013/04/09 14:18:40]

This transferal of ownership of the structure looks mighty dangerous. Also I see
only one use-site of this method (i.e. heap snapshot creation). Could we just
use a second iterator that allows you to iterate over
<Object**,RetainedObjectInfo*> tuples instead of materializing this list here
just to delete it right after iteration again?

[marja, 2013/04/09 16:46:51]

I couldn't wrap my head around how to transfer the ownership of the Info in this
iterator-based approach, so I wrote a version which is closer to the existing
code (HeapSnapshotGenerator modifies directly the data structures of
GlobalHandles, and gets the Info, nullifies the pointer to it and so on). Wdyt?

+  List<ObjectGroup*>* to_return = new List<ObjectGroup*>();
+
+  object_groups_->Sort();
+  retained_object_infos_.Sort();
+  int retained_object_infos_ix = 0;
+
+  void* current_group_id = NULL;
+  size_t current_group_start = 0;
+
+  for (int i = 0; i <= object_groups_->length(); ++i) {
+    if (i == 0)
+      current_group_id = object_groups_->at(i).id;
+    if (i == object_groups_->length() ||
+        current_group_id != object_groups_->at(i).id) {
+      // Group detected: objects in indices [current_group_start, i[.
+      ObjectGroup* group = new ObjectGroup();
+      if (retained_object_infos_ix < retained_object_infos_.length() &&
+          retained_object_infos_[retained_object_infos_ix].id ==
+          object_groups_->at(current_group_start).id) {
+        // Transfer the ownership of info.
+        group->info = retained_object_infos_[retained_object_infos_ix].info;
+        retained_object_infos_[retained_object_infos_ix].info = NULL;
+        ++retained_object_infos_ix;
+      }
+      for (int j = current_group_start; j < i; ++j)
+        group->objects.Add(object_groups_->at(j).object);
+      to_return->Add(group);
+    }
+    if (i < object_groups_->length()) {
+      current_group_id = object_groups_->at(i).id;
+      current_group_start = i;
+    }
+  }
+  return to_return;
+}
 
 void GlobalHandles::RemoveObjectGroups() {
-  for (int i = 0; i < object_groups_.length(); i++) {
-    object_groups_.at(i)->Dispose();
+  object_groups_->Clear();
+  for (int i = 0; i < retained_object_infos_.length(); ++i) {
+    if (retained_object_infos_[i].info != NULL)
+      retained_object_infos_[i].info->Dispose();
   }
-  object_groups_.Clear();
+  retained_object_infos_.Clear();
 }