Spinlock: It spins and locks!

spinlock.hpp

#include <atomic>

class spinlock_mutex {
  public:
    spinlock_mutex() : flag(ATOMIC_FLAG_INIT) {}

    void lock() { while(flag.test_and_set(std::memory_order_acquire)); }
    void unlock() { flag.clear(std::memory_order_release); }

  private:
    std::atomic_flag flag;
};