ceph/src/boost/libs/asio/example/cpp11/futures/daytime_client.cpp

   1 //
   2 // daytime_client.cpp
   3 // ~~~~~~~~~~~~~~~~~~
   4 //
   5 // Copyright (c) 2003-2019 Christopher M. Kohlhoff (chris at kohlhoff dot com)
   6 //
   7 // Distributed under the Boost Software License, Version 1.0. (See accompanying
   8 // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
   9 //
  10
  11 #include <array>
  12 #include <future>
  13 #include <iostream>
  14 #include <thread>
  15 #include <boost/asio/io_context.hpp>
  16 #include <boost/asio/ip/udp.hpp>
  17 #include <boost/asio/use_future.hpp>
  18
  19 using boost::asio::ip::udp;
  20
  21 void get_daytime(boost::asio::io_context& io_context, const char* hostname)
  22 {
  23   try
  24   {
  25     udp::resolver resolver(io_context);
  26
  27     std::future<udp::resolver::results_type> endpoints =
  28       resolver.async_resolve(
  29           udp::v4(), hostname, "daytime",
  30           boost::asio::use_future);
  31
  32     // The async_resolve operation above returns the endpoints as a future
  33     // value that is not retrieved ...
  34
  35     udp::socket socket(io_context, udp::v4());
  36
  37     std::array<char, 1> send_buf  = {{ 0 }};
  38     std::future<std::size_t> send_length =
  39       socket.async_send_to(boost::asio::buffer(send_buf),
  40           *endpoints.get().begin(), // ... until here. This call may block.
  41           boost::asio::use_future);
  42
  43     // Do other things here while the send completes.
  44
  45     send_length.get(); // Blocks until the send is complete. Throws any errors.
  46
  47     std::array<char, 128> recv_buf;
  48     udp::endpoint sender_endpoint;
  49     std::future<std::size_t> recv_length =
  50       socket.async_receive_from(
  51           boost::asio::buffer(recv_buf),
  52           sender_endpoint,
  53           boost::asio::use_future);
  54
  55     // Do other things here while the receive completes.
  56
  57     std::cout.write(
  58         recv_buf.data(),
  59         recv_length.get()); // Blocks until receive is complete.
  60   }
  61   catch (std::system_error& e)
  62   {
  63     std::cerr << e.what() << std::endl;
  64   }
  65 }
  66
  67 int main(int argc, char* argv[])
  68 {
  69   try
  70   {
  71     if (argc != 2)
  72     {
  73       std::cerr << "Usage: daytime_client <host>" << std::endl;
  74       return 1;
  75     }
  76
  77     // We run the io_context off in its own thread so that it operates
  78     // completely asynchronously with respect to the rest of the program.
  79     boost::asio::io_context io_context;
  80     auto work = boost::asio::make_work_guard(io_context);
  81     std::thread thread([&io_context](){ io_context.run(); });
  82
  83     get_daytime(io_context, argv[1]);
  84
  85     io_context.stop();
  86     thread.join();
  87   }
  88   catch (std::exception& e)
  89   {
  90     std::cerr << e.what() << std::endl;
  91   }
  92
  93   return 0;
  94 }