Re: [boost.async] Seeking Endorsement

From: Klemens Morgenstern (klemensdavidmorgenstern_at_[hidden])
Date: 2023-07-27 16:20:36

On Fri, Jul 28, 2023 at 12:15 AM Christian Mazakas via Boost
<boost_at_[hidden]> wrote:
>
> > See what richard said: you can have asio run on io_uring already. You can then
>
> The problem is, this gets said a lot but no one really understands it.
>
> There's a lot to benefit from io_uring that Asio simply can't support
> so saying that
> "Asio can use io_uring" is technically true but it's largely
> disingenuous because it
> neglects all the good parts of io_uring that _can't_ be used. I don't
> wanna derail the
> conversation with all those details but I can expand upon this if required.

Did you look into whether or not you can do that with asio,
by reducing the asio::io_context to just wait for events? And then
initiating all the rest manually. That'd work for async.

>
> > If you want to use your own event loop, you can write an executor for it, too.
>
> I see. Is this as a replacement for the one used internally by Async?

Async needs an executor to use for dispatch & post. Atm the type
defaults to any_io_executor (which is a type erased wrapper).

If you want to change the type we should figure out a solution, it's
possible from my end.
I.e. the config.hpp defines an executor type alias that gets used everywhere,
which could be changed to something else. I just don't know how to
handle includes in the config in a way acceptable for boost.

>
> > Most likely UB. The await_suspend(std::coroutine_handle<T> h)
> > can however grab the executor from the promise,
> > by calling h.promise().get_executor() (after checking with a requires
> > statement) if you need to post back.
>
> Why would this be UB?

Because you'll run thread unsafe code on two threads then. It *shuold*
be fine if you got a single coroutine stack,
but once you select(coro1, coro2) and both resume on different threads
you'll have UB.