Re: [Boost-users] [Boost.Asio] defer, dispatch and post differences?

Subject: Re: [Boost-users] [Boost.Asio] defer, dispatch and post differences?
From: Richard Hodges (hodges.r_at_[hidden])
Date: 2018-01-05 16:05:54

> And how would it know if the handler is a continuation?

Now you're right at the edge of my understanding. I've tried to follow this
stuff through in the asio source code previously.

As I understand it, you can write your own handler objects, rather than
than simply passing in a lambda or bind, which get notified either:
1. once on completion of the entire request, or
2. for every sub-operation of a compound operation such as async_read()

asio figures out which one you mean through some template jiggery-pokery
(technical term) and your handler gets called the right number of times, on
the right thread.

But frankly, this stuff has historically been so under-documented (for my
simply mind) and written in a WORN (write-once, read-never) combination of
macros and template specialisations that I gave up, and limited my ASIO
services to simply invoking a handler function on the correct executor and
letting the client take it from there.

I had hoped to take inspiration from the wonderful but IMHO incomplete AMY
wrapper (https://github.com/liancheng/amy) [mysql wrapped in an asio async
wrapper]. But Cheng seems to have hit the same wall as me, and you can't
handle an async_query with an asio::use_future, for example.

Hopefully the TS will clarify all this over time...

On 5 January 2018 at 16:55, Vinnie Falco via Boost-users <
boost-users_at_[hidden]> wrote:

> On Fri, Jan 5, 2018 at 7:53 AM, Richard Hodges via Boost-users
> <boost-users_at_[hidden]> wrote:
> > Perhaps defer does a post
> > unless the handler is a continuation? I think that would make sense.
>
> And how would it know if the handler is a continuation?
>
> Thanks
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