Add a weak property type to the virtual machine.

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 5337 matching lines @@
     // This is only safe because we create a new Smi, which does not cause
     // heap allocation.
     raw_ptr()->data_length_ = Smi::New(value);
   }
 
   HEAP_OBJECT_IMPLEMENTATION(JSRegExp, Instance);
   friend class Class;
 };
 
 
+class WeakProperty : public Instance {
+ public:
+  RawObject* key() const {
+    return raw_ptr()->key_;
+  }
+
+  void set_key(const Object& key) {
+    StorePointer(&raw_ptr()->key_, key.raw());
+  }
+
+  RawObject* value() const {
+    return raw_ptr()->value_;
+  }
+
+  void set_value(const Object& value) {
+    StorePointer(&raw_ptr()->value_, value.raw());
+  }
+
+  static RawWeakProperty* New(Heap::Space space = Heap::kNew);
+
+  static intptr_t InstanceSize() {
+    return RoundedAllocationSize(sizeof(RawWeakProperty));
+  }
+
+  static void Clear(RawWeakProperty* raw_weak) {

[turnidge, 2012/08/09 18:34:34]

These static functions (Clear/Pop/Push) all are exceptional, in that they take a
Raw type as an argument.  We try not to do this in general, right?  I'm guessing
you are safe since these are really part of the GC implementation.

Would it make sense to move these three functions from WeakProperty to
RawWeakProperty?  That puts them more out of harm's way.

[cshapiro, 2012/08/14 04:58:18]

Removed.  Done.

+    raw_weak->ptr()->key_ = Object::null();
+    raw_weak->ptr()->value_ = Object::null();
+  }
+
+  static RawWeakProperty* Pop(RawWeakProperty** queue) {

[turnidge, 2012/08/09 18:34:34]

Not sure if this is technically a 'queue'.  Seems like its LIFO.  Seems like it
doesn't matter much though.

[cshapiro, 2012/08/14 04:58:18]

True.  This method has been removed.  Done.

+    ASSERT(queue != NULL);
+    RawWeakProperty* result = WeakProperty::null();
+    if (*queue != WeakProperty::null()) {
+      result = *queue;
+      RawWeakProperty* next = result->ptr()->next_;
+      result->ptr()->next_ = WeakProperty::null();
+      *queue = next;
+    }
+    return result;
+  }
+
+  static void Push(RawWeakProperty* raw_weak, RawWeakProperty** queue) {
+    ASSERT(queue != NULL);
+    RawWeakProperty* next = *queue;
+    raw_weak->ptr()->next_ = next;
+    *queue = raw_weak;
+  }
+
+ private:
+  HEAP_OBJECT_IMPLEMENTATION(WeakProperty, Instance);
+  friend class Class;
+};
+
+
 // Breaking cycles and loops.
 RawClass* Object::clazz() const {
   uword raw_value = reinterpret_cast<uword>(raw_);
   if ((raw_value & kSmiTagMask) == kSmiTag) {
     return Smi::Class();
   }
   return Isolate::Current()->class_table()->At(raw()->GetClassId());
 }
 
 
@@ skipping 91 matching lines @@
     if (this->CharAt(i) != str.CharAt(begin_index + i)) {
       return false;
     }
   }
   return true;
 }
 
 }  // namespace dart
 
 #endif  // VM_OBJECT_H_