- Remember the fact that an object has been added to the

runtime/vm/raw_object.h

 // Copyright (c) 2012, 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.
 
 #ifndef VM_RAW_OBJECT_H_
 #define VM_RAW_OBJECT_H_
 
 #include "platform/assert.h"
 #include "vm/globals.h"
 #include "vm/token.h"
@@ skipping 205 matching lines @@
 // be dereferenced (e.g. RawSmi).
 class RawObject {
  public:
   // The tags field which is a part of the object header uses the following
   // bit fields for storing tags.
   enum TagBits {
     kFreeBit = 0,
     kMarkBit = 1,
     kCanonicalBit = 2,
     kFromSnapshotBit = 3,
     kWatchedBit = 4,

[siva, 2013/04/27 00:49:37]

The WatchedBit is only used during GC right so we could swap it with kFreeBit.

-    kReservedTagBit = 5,  // kReservedBit{10K,100K,1M,10M}
-    kReservedTagSize = 3,
+    kRememberedBit = 5,
+    kReservedTagBit = 6,  // kReservedBit{10K,100K,1M,10M}
+    kReservedTagSize = 2,
     kSizeTagBit = 8,
     kSizeTagSize = 8,
     kClassIdTagBit = kSizeTagBit + kSizeTagSize,
     kClassIdTagSize = 16
   };
 
   // Encodes the object size in the tag in units of object alignment.
   class SizeTag {
    public:
     static const intptr_t kMaxSizeTag =
@@ skipping 53 matching lines @@
     ASSERT(!IsMarked());
     uword tags = ptr()->tags_;
     ptr()->tags_ = MarkBit::update(true, tags);
   }
   void ClearMarkBit() {
     ASSERT(IsMarked());
     uword tags = ptr()->tags_;
     ptr()->tags_ = MarkBit::update(false, tags);
   }
 
-  // Support for GC watched bit.
-  bool IsWatched() const {
-    return WatchedBit::decode(ptr()->tags_);
+  // Support for remembered bit.
+  bool IsRemembered() const {
+    return RememberedBit::decode(ptr()->tags_);
   }
-  void SetWatchedBit() {
-    ASSERT(!IsWatched());
+  void SetRememberedBit() {
+    ASSERT(!IsRemembered());
     uword tags = ptr()->tags_;
-    ptr()->tags_ = WatchedBit::update(true, tags);
+    ptr()->tags_ = RememberedBit::update(true, tags);
   }
-  void ClearWatchedBit() {
-    ASSERT(IsWatched());
+  void ClearRememberedBit() {
     uword tags = ptr()->tags_;
-    ptr()->tags_ = WatchedBit::update(false, tags);
+    ptr()->tags_ = RememberedBit::update(false, tags);
   }
 
   // Support for object tags.
   bool IsCanonical() const {
     return CanonicalObjectTag::decode(ptr()->tags_);
   }
   void SetCanonical() {
     uword tags = ptr()->tags_;
     ptr()->tags_ = CanonicalObjectTag::update(true, tags);
   }
   bool IsCreatedFromSnapshot() const {
     return CreatedFromSnapshotTag::decode(ptr()->tags_);
   }
   void SetCreatedFromSnapshot() {
     uword tags = ptr()->tags_;
     ptr()->tags_ = CreatedFromSnapshotTag::update(true, tags);
   }
 
+  // Support for GC watched bit.
+  bool IsWatched() const {
+    return WatchedBit::decode(ptr()->tags_);
+  }
+  void SetWatchedBit() {
+    ASSERT(!IsWatched());
+    uword tags = ptr()->tags_;
+    ptr()->tags_ = WatchedBit::update(true, tags);
+  }
+  void ClearWatchedBit() {
+    ASSERT(IsWatched());
+    uword tags = ptr()->tags_;
+    ptr()->tags_ = WatchedBit::update(false, tags);
+  }
+
   bool IsDartInstance() {
     return (!IsHeapObject() || (GetClassId() >= kInstanceCid));
   }
 
   intptr_t Size() const {
     uword tags = ptr()->tags_;
     intptr_t result = SizeTag::decode(tags);
     if (result != 0) {
       ASSERT(result == SizeFromClass());
       return result;
@@ skipping 36 matching lines @@
   static bool IsBuiltinListClassId(intptr_t index);
   static bool IsTypedDataClassId(intptr_t index);
   static bool IsTypedDataViewClassId(intptr_t index);
   static bool IsExternalTypedDataClassId(intptr_t index);
 
   static intptr_t NumberOfTypedDataClasses();
 
  private:
   uword tags_;  // Various object tags (bits).
 
-  class FreeBit : public BitField<bool, kFreeBit, 1> {};
+  class MarkBit : public BitField<bool, kMarkBit, 1> {};
 
-  class MarkBit : public BitField<bool, kMarkBit, 1> {};
+  class RememberedBit : public BitField<bool, kRememberedBit, 1> {};
 
   class WatchedBit : public BitField<bool, kWatchedBit, 1> {};
 
   class CanonicalObjectTag : public BitField<bool, kCanonicalBit, 1> {};
 
   class CreatedFromSnapshotTag : public BitField<bool, kFromSnapshotBit, 1> {};
 
   class ReservedBits : public BitField<intptr_t,
                                        kReservedTagBit,
                                        kReservedTagSize> {};  // NOLINT
@@ skipping 1262 matching lines @@
   // Make sure this is updated when new TypedData types are added.
   ASSERT(kTypedDataInt8ArrayViewCid == kTypedDataInt8ArrayCid + 12);
   ASSERT(kExternalTypedDataInt8ArrayCid == kTypedDataInt8ArrayViewCid + 13);
   ASSERT(kNullCid == kExternalTypedDataInt8ArrayCid + 12);
   return (kNullCid - kTypedDataInt8ArrayCid);
 }
 
 }  // namespace dart
 
 #endif  // VM_RAW_OBJECT_H_