Re: [boost] Should pass boost::asio::io_service by raw pointer or smart pointer?

Subject: Re: [boost] Should pass boost::asio::io_service by raw pointer or smart pointer?
From: Vinnie Falco (vinnie.falco_at_[hidden])
Date: 2018-12-20 18:52:45

On Wed, Dec 19, 2018 at 10:08 PM Richard Hodges via Boost
<boost_at_[hidden]> wrote:
> Adding some lessons learned over the years to Vinnie's answer, because it's
> not immediately obvious from the ASIO documentation...

Wow... yeah. I have been saying that the "problem" with Asio /
Networking TS is the lack of good documentation and tutorials. And
this is not meant as a slight against the Asio author - it is a pretty
hefty library with big implications and it would be unfair to presume
that the burden of all present and future learning materials should
fall on him. There are folks who think that networking is "too
complicated" but again I feel this would be addressed by having good
literature.

Your post was great, it touched on a lot of good guidelines. We need
this sort of thing in a readily accessible reference format, then I
think networking will be seen in an even more favorable light.

> If you're using strands then all access to your object from
> outside should be via an async function which takes a closure and posts an
> implementation of itself to the current object's strand. This ensures that
> everything runs in the correct thread (which you can assert with
> strand::running_in_this_thread() in your handler functions).

For member functions of application-level classes owning I/O objects,
where those member functions can be called from foreign threads I use
this idiom:

    void session::do_thing(Arg arg)
    {
        if(! strand_.running_in_this_thread())
            return boost::asio::post(
                boost::asio::bind_executor(strand_),
                std::bind(&session::do_thing, shared_from_this(), arg));

        // at this point, the thread of execution is on the strand

        async_do_something(socket_, arg, ...);
    }

This way, do_thing can be called from anywhere.

Regards