Re: [Boost-users] ASIO: custom service which works with spawn/yield

Subject: Re: [Boost-users] ASIO: custom service which works with spawn/yield
From: Cristian Morales Vega (cristian_at_[hidden])
Date: 2018-07-26 11:23:24

On 25 July 2018 at 19:12, Vinnie Falco via Boost-users
<boost-users_at_[hidden]> wrote:
> On Wed, Jul 25, 2018 at 7:25 AM, Cristian Morales Vega via Boost-users
> <boost-users_at_[hidden]> wrote:
>> The following simplified sample shows the problem:
>
> First of all thank you for posting a minimal, complete, and verifiable example.
>
> It looks like your implementation of async_method() is missing one or
> two executor_work_guard objects:
>
> Per N4734[1] 13.2.7.10 Outstanding Work [async.reqmts.async.work]
>
>     1. Until the asynchronous operation has completed, the
> asynchronous operation shall maintain:
>
>     (1.1) — an object work1 of type executor_work_guard, initialized
> as work1(ex1), and where work1.owns_work() == true; and
>
>     (1.2) — an object work2 of type executor_work_guard, initialized
> as work2(ex2), and where work2.owns_work() == true.
>
> I don't think you can get away with just calling `post` from
> `async_method` you need to write a "real" composed operation class
> with all of the bells and whistles including forwarding of the
> associated executor and associated allocator. In this class you can
> store the two required executor_work_guard objects as data members.
>
> A tutorial for writing composed operations may be found here:
>
> <https://www.boost.org/doc/libs/1_67_0/libs/beast/doc/html/beast/using_io/writing_composed_operations.html>
>
> Thanks
>
> [1] <http://cplusplus.github.io/networking-ts/draft.pdf>

13.2.7.1 says

The life cycle of an asynchronous operation is comprised of the
following events and phases:
(2.1)
 — Event 1: The asynchronous operation is started by a call to the
initiating function.
(2.2)
 — Phase 1: The asynchronous operation is now outstanding.
(2.3)
 — Event 2: The externally observable side effects of the asynchronous
operation, if any, are fully established.
The completion handler is submitted to an executor.
(2.4)
 — Phase 2: The asynchronous operation is now completed.

By this definition of "completed" shouldn't my sample code be fine?
This is not supposed to be a composed operation.

In any case I was looking at basic_socket::async_connect() and I
noticed I was using async_completion differently. After changing
"boost::asio::async_completion<ConnectHandler, void(const
boost::system::error_code &)>" for
"boost::asio::async_completion<ConnectHandler,
void(boost::system::error_code)>" (error_code by value, not const
reference) my sample code has started working correctly.

I'm not sure I *really* understand what was going on (or if this
couldn't have been detected at compile time). But... it kind of makes
sense.