[Boost-users] asio async_wait() function question

From: Longyu Mei (lmei007_at_[hidden])
Date: 2008-05-28 10:14:54

I am reading asio tutorial. Cannot understand the
usage of async_wait() function on Timer.3 sample.
http://www.boost.org/doc/libs/1_35_0/doc/html/boost_asio/tutorial/tuttimer3/src.html

//////////////////
void print(const boost::system::error_code& /*e*/,
    boost::asio::deadline_timer* t, int* count)
{
  if (*count < 5)
  {
    std::cout << *count << "\n";
    ++(*count);

    t->expires_at(t->expires_at() +
boost::posix_time::seconds(1));
    t->async_wait(boost::bind(print,
          boost::asio::placeholders::error, t,
count));
  }
}

int main()
{
  boost::asio::io_service io;

  int count = 0;
  boost::asio::deadline_timer t(io,
boost::posix_time::seconds(1));
  t.async_wait(boost::bind(print,
        boost::asio::placeholders::error, &t,
&count));

  io.run();

  std::cout << "Final count is " << count << "\n";

  return 0;
}

/////////////////

in the main(), the async_wait() will not be invoked
until the io.run() is called.

But inside the print() there is a async_wait() call.
Why we don't need run() to trigger it?

thanks,