Question

I rewrite a boost.asio example “Timer.3 – Binding arguments to a handler”. I think “worker” can work forever and “print” can be called each second. But “print” only is called once. It is very diffcult for me to think why.

If this can’t work,how can I do other things except “async_wait” in one single thread.

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

int num = 0;
void worker(){
    while(1){
        ++num;
    }
}
void print(const boost::system::error_code& /*e*/,
    boost::asio::deadline_timer* t, int* count)
{
    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
    ));
    if(*count == 1){
        worker();
    }
}

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;
}

Answer 1

You have an infinite loop

void worker() {
    while(1) {
        ++num;
    }
}

so control never returns the first time print() is invoked.