C++ semaphore

sema.cpp

class Semaphore {
      public:
        void post() {
          std::lock_guard<std::mutex> lock(mutex_);
          count_ += 1;
          cv_.notify_one();
        }
        
        void shutdown() {
          std::lock_guard<std::mutex> lock(mutex_);
          cv_.notify_all();
          count_ = 0;
        }
        
        template<typename Predicate>
        void wait(Predicate predicate) {
          std::unique_lock<std::mutex> lock(mutex_);
          cv_.wait(lock, [this, predicate]{ return predicate() || count_ > 0; });
          if (count_ > 0) {
           --count_;
          }
        }
        
      private:
        size_t count_{0};
        std::condition_variable cv_;
        std::mutex mutex_;
      };