class Latch {
  uint32_t Count;
  mutable std::mutex Mutex;
  mutable std::condition_variable Cond;
 
public:
  explicit Latch(uint32_t Count = 0) : Count(Count) {}
  ~Latch() { sync(); }

  void inc() {
    std::lock_guard<std::mutex> lock(Mutex);
    ++Count;
  }
  
  void dec() {
    std::lock_guard<std::mutex> lock(Mutex);
    if (--Count == 0)
      Cond.notify_all();
  }
   
  void sync() const {
    std::unique_lock<std::mutex> lock(Mutex);
    Cond.wait(lock, [&] { return Count == 0; });
  }
};