Request for comments on overall approach.

runtime/vm/gc_marker.cc

 // Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/gc_marker.h"
 
 #include "vm/allocation.h"
 #include "vm/dart_api_state.h"
 #include "vm/isolate.h"
 #include "vm/pages.h"
@@ skipping 121 matching lines @@
     }
   }
 
  private:
   void MarkAndPush(RawObject* raw_obj) {
     ASSERT(raw_obj->IsHeapObject());
     ASSERT(page_space_->Contains(RawObject::ToAddr(raw_obj)));
 
     // Mark the object and push it on the marking stack.
     ASSERT(!raw_obj->IsMarked());
-    RawClass* raw_class = raw_obj->ptr()->class_;
+    // TODO(vegorov): consider moving it to a separate helper method.
+    RawClass* raw_class = raw_obj->GetClass();

[Ivan Posva, 2012/05/26 04:34:46]

This does not need to be done early anymore as the marking bit does not
interfere with reading the class.

     raw_obj->SetMarkBit();
     marking_stack_->Push(raw_obj);
 
     // Update the number of used bytes on this page for fast accounting.
     HeapPage* page = PageSpace::PageFor(raw_obj);
     page->AddUsed(raw_obj->Size());
 
     // TODO(iposva): Should we mark the classes early?
     MarkObject(raw_class);

[Ivan Posva, 2012/05/26 04:34:46]

How about
MarkClass(raw_obj->ClassId());
or something similar? Within the MarkingVisitor we already have the isolate
handy by way of heap so it should be much cheaper than looking it up during
raw_obj->GetClass().

[Vyacheslav Egorov (Google), 2012/05/26 16:48:22]

Nice idea. Will do.

   }
 
   void MarkObject(RawObject* raw_obj) {
     // Fast exit if the raw object is a Smi.
     if (!raw_obj->IsHeapObject()) return;
 
     // Fast exit if the raw object is marked.
     if (raw_obj->IsMarked()) return;
 
     // Skip over new objects, but verify consistency of heap while at it.
@@ skipping 155 matching lines @@
   MarkingVisitor mark(heap_, page_space, &marking_stack);
   IterateRoots(isolate, &mark, !invoke_api_callbacks);
   DrainMarkingStack(isolate, &mark);
   IterateWeakReferences(isolate, &mark);
   MarkingWeakVisitor mark_weak;
   IterateWeakRoots(isolate, &mark_weak, invoke_api_callbacks);
   Epilogue(isolate, invoke_api_callbacks);
 }
 
 }  // namespace dart