Decoupling MarkDescriptorArray as much as possible from the ContentArray.

src/objects.cc

 // Copyright 2012 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 5820 matching lines @@
       MaybeObject* copy_result =
           new_descriptors->CopyFrom(next_descriptor++, this, i, witness);
       if (copy_result->IsFailure()) return copy_result;
     }
   }
   ASSERT(next_descriptor == new_descriptors->number_of_descriptors());
 
   return new_descriptors;
 }
 
-
+// We need the whiteness witness since sort will reshuffle the entries in the
+// descriptor array. If the descriptor array were to be gray, the sort would
+// potentially swap a black and a white member. This would resulting in

[Michael Starzinger, 2012/05/24 14:28:54]

Reasoning is off.

[...] were to be black, the shuffling would move a slot that was already
recorded as pointing into an evacuation candidate. This would result in missing
updates upon evacuation.

[Toon Verwaest, 2012/05/25 12:27:26]

Done.

+// accidentally reclaiming the white member if the descriptor array owned the
+// unique pointer.
 void DescriptorArray::SortUnchecked(const WhitenessWitness& witness) {
   // In-place heap sort.
   int len = number_of_descriptors();
 
   // Bottom-up max-heap construction.
   // Index of the last node with children
   const int max_parent_index = (len / 2) - 1;
   for (int i = max_parent_index; i >= 0; --i) {
     int parent_index = i;
     const uint32_t parent_hash = GetKey(i)->Hash();
@@ skipping 7088 matching lines @@
   set_year(Smi::FromInt(year), SKIP_WRITE_BARRIER);
   set_month(Smi::FromInt(month), SKIP_WRITE_BARRIER);
   set_day(Smi::FromInt(day), SKIP_WRITE_BARRIER);
   set_weekday(Smi::FromInt(weekday), SKIP_WRITE_BARRIER);
   set_hour(Smi::FromInt(hour), SKIP_WRITE_BARRIER);
   set_min(Smi::FromInt(min), SKIP_WRITE_BARRIER);
   set_sec(Smi::FromInt(sec), SKIP_WRITE_BARRIER);
 }
 
 } }  // namespace v8::internal