Question

I am trying to understand the difference between io_service’s poll()/poll_one() and run()/run_one(). The difference as stated in the documentation is that poll() executes ready handlers as opposed to run() which executes any handler.

But nowhere in the boost documentation could I find the definition of a ‘ready handler’.

A valid answer to this question is one able to show, preferably with a code example, the difference between a ready and non-ready handler and the difference between how poll() and run() executes it.

Thanks.

Answer 1

int main()
{
    boost::asio::io_service io_service;
    boost::asio::deadline_timer timer(io_service);

    timer.expires_from_now(boost::posix_time::seconds(5));
    timer.async_wait([](const boost::system::error_code& err)
                     { std::cout << (err ? "error" : "okay")
                     ;});

    //io_service.poll_one(); 
    io_service.run_one();
}

If you use io_service.poll_one(); you will most likely not see any output because the timer has not elapsed yet. ready handler simply means a handle that is ready to run (such as when a timer elapses or an operation finishes, etc.). However, if you use io_service.run_one(); this call will block until the timer finishes and execute the handler.