Boost Asio总结（8）class work

1. 调用run()后，即使没有io事件, 也不会退出事件循环, 而是一直等待, 当有了新的异步io调用的时候, 还可以继续使用该循环。 asio::io_context::work可以防止io_context在没有io事件的情退出

int main()
{
    
      
    asio::io_context ioc;
    asio::ip::tcp::endpoint ep(asio::ip::address::from_string("127.0.0.1"), 6768);
    asio::ip::tcp::socket sock(ioc, ep.protocol());
    asio::ip::tcp::socket sock1(ioc, ep.protocol());
 
    asio::io_context::work worker(ioc);
    std::thread t([&ioc]() {
    
    ioc.run(); });
   
    sock.async_connect(ep, [](const std::error_code & err) {
    
    
        if (err.value() != 0) {
    
    
            std::cout << "Error: " << err.message() << std::endl;
        }
    });
    
    sock1.async_connect(ep, [](const std::error_code & err) {
    
    
        if (err.value() != 0) {
    
    
            std::cout <<"Error: "<< err.message() << std::endl;
        }
    });
   
    std::cout << "Main thread will for 3 seconds...\n";  // 防止stop()执行过快
    std::this_thread::sleep_for(std::chrono::seconds(3));
    std::cout << "Main thread weak up...\n";
    ioc.stop();  // 显式停止io_context, 否则无法终止
    t.join();
 
    return 0;
}

2.

class io_context
::work
{
    
    
public:
  /// Constructor notifies the io_context that work is starting.
  /**
   * The constructor is used to inform the io_context that some work has begun.
   * This ensures that the io_context object's run() function will not exit
   * while the work is underway.
   */
  explicit work(boost::asio::io_context& io_context);

  /// Copy constructor notifies the io_context that work is starting.
  /**
   * The constructor is used to inform the io_context that some work has begun.
   * This ensures that the io_context object's run() function will not exit
   * while the work is underway.
   */
  work(const work& other);

  /// Destructor notifies the io_context that the work is complete.
  /**
   * The destructor is used to inform the io_context that some work has
   * finished. Once the count of unfinished work reaches zero, the io_context
   * object's run() function is permitted to exit.
   */
  ~work();

  /// Get the io_context associated with the work.
  boost::asio::io_context& get_io_context();

private:
  // Prevent assignment.
  void operator=(const work& other);

  // The io_context implementation.
  detail::io_context_impl& io_context_impl_;
};
#endif // !defined(BOOST_ASIO_NO_DEPRECATED)



#if !defined(BOOST_ASIO_NO_DEPRECATED)
inline io_context::work::work(boost::asio::io_context& io_context)
  : io_context_impl_(io_context.impl_)
{
    
    
  io_context_impl_.work_started();
}

inline io_context::work::work(const work& other)
  : io_context_impl_(other.io_context_impl_)
{
    
    
  io_context_impl_.work_started();
}

inline io_context::work::~work()
{
    
    
  io_context_impl_.work_finished();
}

inline boost::asio::io_context& io_context::work::get_io_context()
{
    
    
  return static_cast<boost::asio::io_context&>(io_context_impl_.context());
}
#endif // !defined(BOOST_ASIO_NO_DEPRECATED)