boost::asio序列: 多線程

 示例代碼中，在原來boost::asio代碼基礎上，增加了打印線程id的代碼，方便理解多線程執行boost::asio::io_context::run()（或 boost::asio::io_service::run()）的特點，同時，在這個示例中，學習boost::asio::io_context::strand的作用，就是，控制執行的順序，先加入的先執行

#include <iostream>
#include <boost/asio.hpp>
#include <boost/thread/thread.hpp>
#include <boost/bind.hpp>
#include <boost/date_time/posix_time/posix_time.hpp>

class printer
{
public:
  printer(boost::asio::io_context& io)
    : strand_(io),
      timer1_(io, boost::posix_time::seconds(1)),
      timer2_(io, boost::posix_time::seconds(1)),
      count_(0)
  {
    timer1_.async_wait(boost::asio::bind_executor(strand_,
          boost::bind(&printer::print1, this)));

    timer2_.async_wait(boost::asio::bind_executor(strand_,
          boost::bind(&printer::print2, this)));
  }

  ~printer()
  {
    std::cout << "Final count is " << count_ << std::endl;
  }

  void print1()
  {
    if (count_ < 10)
    {
      std::cout << "threadid = " << boost::this_thread::get_id() << "=> Timer 1: " << count_ << std::endl;
      ++count_;

      timer1_.expires_at(timer1_.expires_at() + boost::posix_time::seconds(1));

      timer1_.async_wait(boost::asio::bind_executor(strand_,
            boost::bind(&printer::print1, this)));
    }
  }

  void print2()
  {
    if (count_ < 10)
    {
      std::cout << "threadid = " << boost::this_thread::get_id() << " => Timer 2: " << count_ << std::endl;
      ++count_;

      timer2_.expires_at(timer2_.expires_at() + boost::posix_time::seconds(1));

      timer2_.async_wait(boost::asio::bind_executor(strand_,
            boost::bind(&printer::print2, this)));
    }
  }

private:
  boost::asio::io_context::strand strand_;
  boost::asio::deadline_timer timer1_;
  boost::asio::deadline_timer timer2_;
  int count_;
};

int main()
{
  boost::asio::io_context io;
  printer p(io);
  boost::thread t(boost::bind(&boost::asio::io_context::run, &io));
  io.run();
  t.join();

  return 0;
}

實際上，就是超時事件完成Handler可以在兩個線程中執行：在線程t或main線程中，如下打印結果：