C++ co-routines are coming soon...

[Andrei Kartashev]

Thank you for your effort here!
This three are really long waiting 'must have' things.
I will try to test this proposal.

On Sun, 2021-11-28 at 15:22 -0600, Patrick Williams wrote:
> Hello,
> 
> I just pushed up some code I've been working on for initial community
> preview:
> C++20 coroutine support in sdbusplus[1].  This code should be
> considered
> "experimental" for the time-being but a good preview of where I plan
> to take the
> sdbusplus bindings.  I know there are complaints about the current
> sdbusplus
> support in one of three veins depending on your perspective of
> importance:
> 
>     1. The current sdbusplus server bindings in phosphor-dbus-
> interfaces are
>        synchronous.
>     2. There are no sdbusplus client bindings in phosphor-dbus-
> interfaces.
>     3. The code using the sdbusplus Boost/ASIO interfaces is very
> callback
>        intensive (and difficult to read).
> 
> I've been wanting to leverage C++20 coroutines for quite a while in
> order to
> address these shortcomings but haven't gotten around to it due to
> lack of
> understanding on my part (and lack of time to fix this) and lack of
> maturity in
> the library support.  There is a proposal for C++23 (P2300)[2] which
> attempts to
> fix the "maturity" problem and the authors of that have been using
> libunifex[3]
> as their proving ground.  Using libunifex and becoming enlightened by
> Eric
> Niebler's excellent talk at CppCon'21, I've finally been able to make
> some good
> progress on this.
> 
> There will be more to come, but I wanted to give a taste of what a
> C++20
> co-routine-based sdbusplus agent might look like.  This is an example
> of a
> task that reacts to D-Bus "NameOwnerChanged" signals:
> 
> ```
> auto watch_events(sdbusplus::async::context_t& ctx)
>     -> sdbusplus::execution::task<void>
> {
>     using namespace sdbusplus::async::match;
>     auto m = match(ctx, rules::nameOwnerChanged());
> 
>     while (auto msg = co_await m.next())
>     {
>         std::string service, old_name, new_name;
>         msg.read(service, old_name, new_name);
>         if (!new_name.empty())
>         {
>             std::cout << new_name << " owns " << service <<
> std::endl;
>         }
>         else
>         {
>             std::cout << service << " released" << std::endl;
>         }
>     };
> 
>     co_return;
> }
> ```
> 
> I currently have `match` implemented and I plan to get `call` working
> very soon.
> Sometime between now and late January I'll probably do an educational
> talk on
> co-routines.
> 
> 1. https://gerrit.openbmc-project.xyz/c/openbmc/sdbusplus/+/49117
> 2. https://github.com/cplusplus/papers/issues/1054
> 3. https://github.com/facebookexperimental/libunifex
> 4. https://www.youtube.com/watch?v=xLboNIf7BTg
> 

-- 
Best regards,
Andrei Kartashev