[heap] Concurrency support for heap book-keeping info

src/atomic-utils.h

 // Copyright 2015 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_ATOMIC_UTILS_H_
 #define V8_ATOMIC_UTILS_H_
 
 #include <limits.h>
 
 #include "src/base/atomicops.h"
@@ skipping 12 matching lines @@
     base::NoBarrier_AtomicIncrement(&value_,
                                     static_cast<base::AtomicWord>(increment));
   }
 
   V8_INLINE T Value() { return static_cast<T>(base::NoBarrier_Load(&value_)); }
 
   V8_INLINE void SetValue(T new_value) {
     base::NoBarrier_Store(&value_, static_cast<base::AtomicWord>(new_value));
   }
 
+  V8_INLINE T operator=(T value) {
+    SetValue(value);
+    return value;
+  }
+
  private:
   STATIC_ASSERT(sizeof(T) <= sizeof(base::AtomicWord));
 
   base::AtomicWord value_;
 };
 
 
 // Flag using T atomically. Also accepts void* as T.
 template <typename T>
 class AtomicValue {
  public:
+  AtomicValue() : value_(0) {}
+
   explicit AtomicValue(T initial)
       : value_(cast_helper<T>::to_storage_type(initial)) {}
 
   V8_INLINE T Value() {
     return cast_helper<T>::to_return_type(base::NoBarrier_Load(&value_));
   }
 
   V8_INLINE bool TrySetValue(T old_value, T new_value) {
     return base::NoBarrier_CompareAndSwap(
                &value_, cast_helper<T>::to_storage_type(old_value),
@@ skipping 106 matching lines @@
     return static_cast<base::AtomicWord>(1) << element;
   }
 
   base::AtomicWord bits_;
 };
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // #define V8_ATOMIC_UTILS_H_