example : thread pool + increase asio threads

[madkote]

I am looking for minimal example:

• dispatch cpu work function on a thread pool
• how to increase asio threads (cobalt is single threaded, but in plain asio additional io threads can be added with io_threads.emplace_back([&io_main]() { io_main.run(); };)

[klemens-morgenstern]

1. Are you thinking about a specific thread-pool?
2. What do you mean? Cobalt won't work if you add more threads.

[madkote]

thanks for reply @klemens-morgenstern

1. normally there are two options

• using explicit thread pool as in examples
• use another io context work cpu intesive work (switch it when needed and code stays async)

2. I was looking for a way to add more threads to main IO and if that would work with cobalt (I have not tried it yet) background: starting asio::io_context io_main in more then one threads will add throughput for the handling. Therefore the question, if cobalt relies on ONE context with one thread or is there a possibility to set custom IO context?

[klemens-morgenstern]

You can just use spawn on a single threaded executor, and you should use cobalt::this_thread::set_executor from within.

boost::cobalt::task<void> my_task()
{
  boost::cobalt::this_thread::set_executor(co_await boost::cobalt::this_coro::executor);
  // do your work here
}

asio::thread_pool tp;
boost::cobalt::spawn(asio::make_strand(tp), my_task(), asio::detached);

You can also use spawn accross threads with use_op, e.g.:

cobalt::main co_main(int, char**)
{
   asio::thread_pool tp;
  // run the task on another thread
  co_await cobalt::spawn(asio::make_strand(tp), my_task(), cobalt::use_op);
  co_return 0;
}

co_main does something very similar, but also connects the signals to cancellations, so that SIGTERM causes a graceful shutdown.