std::atomic_ref::notify_one

#include <iostream>
#include <atomic>
#include <thread>

class my_mutex {
  bool state_ = false; // false:unlock, true:lock
public:
  void lock() noexcept {
    std::atomic_ref r{state_};
    while (r.exchange(true) == true) {
      r.wait(true);
    }
  }

  void unlock() noexcept {
    std::atomic_ref r{state_};
    r.store(false);
    r.notify_one();
  }
};

my_mutex mut;
void print(int x) {
  mut.lock();
  std::cout << x << std::endl;
  mut.unlock();
}

int main()
{
  std::thread t1 {[] {
    for (int i = 0; i < 5; ++i) {
      print(i);
    }
  }};
  std::thread t2 {[] {
    for (int i = 5; i < 10; ++i) {
      print(i);
    }
  }};

  t1.join();
  t2.join();
}