common/atomic.h

   1 #ifndef AL_ATOMIC_H
   2 #define AL_ATOMIC_H
   3
   4 #include <atomic>
   5
   6
   7 using RefCount = std::atomic<unsigned int>;
   8
   9 inline void InitRef(RefCount &ref, unsigned int value)
  10 { ref.store(value, std::memory_order_relaxed); }
  11 inline unsigned int ReadRef(RefCount &ref)
  12 { return ref.load(std::memory_order_acquire); }
  13 inline unsigned int IncrementRef(RefCount &ref)
  14 { return ref.fetch_add(1u, std::memory_order_acq_rel)+1u; }
  15 inline unsigned int DecrementRef(RefCount &ref)
  16 { return ref.fetch_sub(1u, std::memory_order_acq_rel)-1u; }
  17
  18
  19 /* WARNING: A livelock is theoretically possible if another thread keeps
  20  * changing the head without giving this a chance to actually swap in the new
  21  * one (practically impossible with this little code, but...).
  22  */
  23 template<typename T>
  24 inline void AtomicReplaceHead(std::atomic<T> &head, T newhead)
  25 {
  26     T first_ = head.load(std::memory_order_acquire);
  27     do {
  28         newhead->next.store(first_, std::memory_order_relaxed);
  29     } while(!head.compare_exchange_weak(first_, newhead,
  30             std::memory_order_acq_rel, std::memory_order_acquire));
  31 }
  32
  33 #endif /* AL_ATOMIC_H */