class thread_pool {
  std::atomic_bool done;
  thread_safe_queue<std::function<void()>> work_queue;
  std::vector<std::thread> threads;
  join_threads joiner;

  void worker_thread()
  {
    while (!done) {
      std::function<void()> task;
      if (work_queue.try_pop(task)) {
        task();
      }
      else {
        std::this_thread::yield();
      }
    }
  }

public:
  thread_pool() : done(false), joiner(threads)
  {
    unsigned const thread_count = std::thread::hardware_concurrency();
    try {
      for (unsigned i = 0; i < thread_count; ++i) {
        threads.push_back(std::thread(&thread_pool::worker_thread, this));
      }
    }
    catch (...) {
      done = true;
      throw;
    }
  }

  ~thread_pool() { done = true; }

  template <typename FunctionType>
  void submit(FunctionType f)
  {
    work_queue.push(std::function<void()>(f));
  }
};