one task previleged in asio io_service - boost-asio

Question

I have io_service with one task (deadline_timer) that is fired every 1 sec.
Next, I want to create new thread by thread t1(bind(&io_service::run, &ios)); for some other tasks.
How to be sure (if possible) that deadline_timer will not be interrupted? Or better, be sure that it has own thread.

Answer 1

To guarantee that an I/O object, such as a deadline_timer, has its own dedicated thread, one could use multiple io_service objects:
an io_service for the timer processed by a single thread or group of threads
an io_service for all other tasks and I/O objects processed by a different thread or different group of threads
Using multiple io_service objects can help prevent contention between event handling and dispatching. For example, an io_service will not be impacted by a completion handler that is taking a long time to complete within a different io_service. However, all threads are still subject to the OS scheduler, where interruptions may occur.
Below is an example demonstrating using multiple io_service objects, where a deadline_timer is being processed by a dedicated thread:
#include <iostream>
#include <thread>
#include <boost/asio.hpp>
void arm_timer(boost::asio::deadline_timer& timer)
{
timer.expires_from_now(boost::posix_time::milliseconds(500));
timer.async_wait([&timer]
(const boost::system::error_code& error)
{
std::cout << "timer: " << error.message() << std::endl;
arm_timer(timer);
});
}
int main()
{
// Dedicate an io_service and thread to a single timer.
boost::asio::io_service timer_io_service;
boost::asio::deadline_timer timer(timer_io_service);
arm_timer(timer);
std::thread timer_thread([&timer_io_service]() {
timer_io_service.run();
});
// Use a different io_service for other tasks.
boost::asio::io_service io_service;
// Post a tasks to stop the timer io_service.
io_service.post([&timer_io_service]{
timer_io_service.stop();
});
// Let timer run.
std::this_thread::sleep_for(std::chrono::seconds(2));
io_service.run();
timer_thread.join();
}