thread 并发

class thread_guard
{
  std::thread& t;
public:
  explicit thread_guard(std::thread& t_):
    t(t_)
  {}
  ~thread_guard()
  {
    if(t.joinable()) // 1
    {
      t.join();      // 2
    }
  }
  thread_guard(thread_guard const&)=delete;   // 3
  thread_guard& operator=(thread_guard const&)=delete;
};