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

Subject: Re: [Boost-users] [Boost.Asio] defer, dispatch and post differences?
From: Vinnie Falco (vinnie.falco_at_[hidden])
Date: 2018-01-05 16:10:11

On Fri, Jan 5, 2018 at 8:05 AM, Richard Hodges via Boost-users
<boost-users_at_[hidden]> wrote:
>> And how would it know if the handler is a continuation?
>
> 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.

I don't think that is correct. Pre Net-TS, Asio considered a handler
to be a continuation if the function asio_handler_is_continuation
returned `true` when passed a pointer to an instance of that handler
type. The new Asio does not use this mechanism. Instead, it requires
that the caller use post() if the handler is not a continuation and
defer() if it is. So the caller informs the implementation whether or
not the handler is a continuation, just like before but by invoking
the correct function.

However, it is not clear how to accomplish that. Which is why an
example would be helpful.

Thanks