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: 2018-12-21 03:02:32

On Thu, Dec 20, 2018 at 6:45 PM Richard Hodges <hodges.r_at_[hidden]> wrote:
> ...even with Vinnie's easy to follow guide, it requires a hundred lines of
> boilerplate to implement what amounts to one async method.

Yes, that is kind of irritating. I've been working on some tools to
make it easier.

The function wrap_handler returns a new completion handler which wraps
your function object (lambda) and inherits the allocator and executor
of another completion handler:

<https://github.com/vinniefalco/beast/blob/8afbc6090bded0cdfda46871d829ea778aa80ced/include/boost/beast/_experimental/core/detail/wrap_handler.hpp#L88>

The class template base_handler<> is meant as a base class for
composed operations, it holds the handler for you and it provides all
the hooks. I notice that you didn't include an overload for
asio_handler_invoke in your example, which will certainly cause
undefined behavior in some cases:

<https://github.com/vinniefalco/beast/blob/8afbc6090bded0cdfda46871d829ea778aa80ced/include/boost/beast/_experimental/core/detail/handler_base.hpp#L27>

You can see both wrap_handler and handler_base used together to
implement a composed operation, a flavor of async_read_some which has
a built-in timeout:

<https://github.com/vinniefalco/beast/blob/8afbc6090bded0cdfda46871d829ea778aa80ced/include/boost/beast/_experimental/core/impl/basic_timed_stream.hpp#L42>

In particular, handler_base let me leave out all of the boilerplate
which is nice. It is possible that with some adaptation these
utilities can be used to achieve the result you desire.

These experimental features will appear in Boost.Beast version 1.70.0.

Regards