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#ifndef AL_ATOMIC_H
#define AL_ATOMIC_H
#include <atomic>
#include <utility>
namespace al {
struct atomic_invflag : protected std::atomic_flag {
atomic_invflag() noexcept = default;
template<typename T>
atomic_invflag(T&& arg) noexcept : std::atomic_flag{std::forward<T>(arg)} { }
inline bool test_and_clear(std::memory_order m=std::memory_order_seq_cst) noexcept
{ return !test_and_set(m); }
inline bool test_and_clear(std::memory_order m=std::memory_order_seq_cst) volatile noexcept
{ return !test_and_set(m); }
inline void set(std::memory_order m=std::memory_order_seq_cst) noexcept
{ clear(m); }
inline void set(std::memory_order m=std::memory_order_seq_cst) volatile noexcept
{ clear(m); }
};
} // namespace al
using RefCount = std::atomic<unsigned int>;
inline void InitRef(RefCount &ref, unsigned int value)
{ ref.store(value, std::memory_order_relaxed); }
inline unsigned int ReadRef(RefCount &ref)
{ return ref.load(std::memory_order_acquire); }
inline unsigned int IncrementRef(RefCount &ref)
{ return ref.fetch_add(1u, std::memory_order_acq_rel)+1u; }
inline unsigned int DecrementRef(RefCount &ref)
{ return ref.fetch_sub(1u, std::memory_order_acq_rel)-1u; }
/* WARNING: A livelock is theoretically possible if another thread keeps
* changing the head without giving this a chance to actually swap in the new
* one (practically impossible with this little code, but...).
*/
template<typename T>
inline void AtomicReplaceHead(std::atomic<T> &head, T newhead)
{
T first_ = head.load(std::memory_order_acquire);
do {
newhead->next.store(first_, std::memory_order_relaxed);
} while(!head.compare_exchange_weak(first_, newhead,
std::memory_order_acq_rel, std::memory_order_acquire));
}
#endif /* AL_ATOMIC_H */
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