- Add AtomicOperations::CompareAndSwapWord

runtime/vm/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_OBJECT_H_
 #define VM_OBJECT_H_
 
 #include "include/dart_api.h"
 #include "platform/assert.h"
 #include "platform/utils.h"
@@ skipping 212 matching lines @@
 class Object {
  public:
   virtual ~Object() { }
 
   RawObject* raw() const { return raw_; }
   void operator=(RawObject* value) {
     initializeHandle(this, value);
   }
 
   void set_tags(intptr_t value) const {
+    ASSERT(!IsNull());
     // TODO(asiva): Remove the capability of setting tags in general. The mask
     // here only allows for canonical and from_snapshot flags to be set.

[koda, 2014/09/02 04:18:31]

Before masking (i.e., ignoring part of the input...), please assert that the old
and new tag value only differ on those flags:
ASSERT(((value ^ tags) & ~static_cast<uword>(0xc)) == 0);

Also, please put 0x0...c into a uword-typed local constant and file an issue for
the TODO.

-    ASSERT(!IsNull());
-    uword tags = raw()->ptr()->tags_ & ~0x0000000c;
-    raw()->ptr()->tags_ = tags | (value & 0x0000000c);
+    value = value & 0x0000000c;
+    uword tags = raw()->ptr()->tags_;
+    uword old_tags;
+    do {
+      old_tags = tags;
+      uword new_tags = (old_tags & ~0x0000000c) | value;
+      tags = AtomicOperations::CompareAndSwapWord(
+          &raw()->ptr()->tags_, old_tags, new_tags);
+    } while (tags != old_tags);
   }
   void SetCreatedFromSnapshot() const {
     ASSERT(!IsNull());
     raw()->SetCreatedFromSnapshot();
   }
   bool IsCanonical() const {
     ASSERT(!IsNull());
     return raw()->IsCanonical();
   }
   void SetCanonical() const {
@@ skipping 7161 matching lines @@
 
 
 RawObject* MegamorphicCache::GetTargetFunction(const Array& array,
                                                intptr_t index) {
   return array.At((index * kEntryLength) + kTargetFunctionIndex);
 }
 
 }  // namespace dart
 
 #endif  // VM_OBJECT_H_