Re: "C++20 Coroutines" by Martin Bond

From	Manfred <noname@add.invalid>
Newsgroups	comp.lang.c++
Subject	Re: "C++20 Coroutines" by Martin Bond
Date	2021-09-25 23:07 +0200
Organization	Aioe.org NNTP Server
Message-ID	<sio33e$1248$1@gioia.aioe.org> (permalink)
References	<siauhc$mg6$1@dont-email.me> <sin7c5$c9d$1@dont-email.me>

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On 9/25/2021 3:14 PM, Alf P. Steinbach wrote:
> On 20 Sep 2021 23:30, Lynn McGuire wrote:
>> "C++20 Coroutines" by Martin Bond
>>     https://blog.feabhas.com/2021/09/c20-coroutines/
>>
>> "There seems to be a lot of confusion around the implementation of 
>> C++20 coroutines, which I think is due to the draft technical 
>> specification for C++20 stating that coroutines are a work in progress 
>> so we can’t expect full compiler and library support at this point in 
>> time.
>> A lot of the problems probably arise from the lack of official 
>> documentation about working with coroutines. We have been given C++ 
>> syntax support for coroutines (the co_yield and co_return) but without 
>> all of what I consider full library support. The standard library has 
>> hooks and basic functionality for supporting coroutines, but we must 
>> incorporate this into our own classes. I anticipate that there will be 
>> full library support for generator style coroutines in C++23."
> 
> The main confusion about C++20 “coroutines” is that they're general 
> coroutines.
> 
> They're not: they're simple continuations, the special case of 
> /stackless/ coroutines (no dedicated stack for each coroutine).
> 
> While that's nice performance-wise it's very limited, and the Microsoft 
> style support framework adopted in C++20 requires you to build a full 
> fledged star ship in order to lift a little pebble; it's, well, moronic.
> 
> ---
> 
> I once started coding up real coroutines in terms of standard C++ threads.
> 
> That could be very useful, in contrast to the mostly useless C++17 
> continuations.
> 
> However, I stopped fiddling with it when the complexity of the 
> implementation overwhelmed me. No doubt because of a lack of experience 
> in safe multi-tasking. It would be really nice if SOMEONE could do this: 
> real general coroutines, by leveraging real C++ threads.
> 
> ---
> 
> That could open the world of safe multi-tasking to C++ programmers in 
> general.

I'm no expert in coroutines, but AFAIU their main advantage is to enable 
multitasking without the overhead of multithreading.
In order to achieve this, language support is needed that was just not 
available prior to C++20 (and even with C++20 such support is limited, 
so that only the subset of continuations is actually available, as you say)

The point being, if you try to do that using threads kind of defeats the 
purpose, doesn't it?
(even if you build this with full synchronization inside, you'll still 
pay the price of performance and resource usage, which can be relevant 
for this kind of thing)

> 
> Another such enabler: an implementation of Ada-like rendezvous.
> 
> And, and, ... Occam-like channels, maybe. :)
> 
> 
> - Alf

Thread

"C++20 Coroutines" by Martin Bond Lynn McGuire <lynnmcguire5@gmail.com> - 2021-09-20 16:30 -0500
  Re: "C++20 Coroutines" by Martin Bond Bo Persson <bo@bo-persson.se> - 2021-09-21 09:28 +0200
  Re: "C++20 Coroutines" by Martin Bond Bonita Montero <Bonita.Montero@gmail.com> - 2021-09-21 11:45 +0200
    Re: "C++20 Coroutines" by Martin Bond HorseyWorsey@the_stables.com - 2021-09-21 15:37 +0000
      Re: "C++20 Coroutines" by Martin Bond Bonita Montero <Bonita.Montero@gmail.com> - 2021-09-21 17:40 +0200
      Re: "C++20 Coroutines" by Martin Bond Juha Nieminen <nospam@thanks.invalid> - 2021-09-22 05:22 +0000
        Re: "C++20 Coroutines" by Martin Bond HorseyWorsey@the_stables.com - 2021-09-22 09:26 +0000
          Re: "C++20 Coroutines" by Martin Bond Bonita Montero <Bonita.Montero@gmail.com> - 2021-09-22 16:40 +0200
            Re: "C++20 Coroutines" by Martin Bond HorseyWorsey@the_stables.com - 2021-09-22 15:01 +0000
              Re: "C++20 Coroutines" by Martin Bond Bonita Montero <Bonita.Montero@gmail.com> - 2021-09-23 05:38 +0200
                Re: "C++20 Coroutines" by Martin Bond Branimir Maksimovic <branimir.maksimovic@gmail.com> - 2021-09-23 09:05 +0000
                Re: "C++20 Coroutines" by Martin Bond Bonita Montero <Bonita.Montero@gmail.com> - 2021-09-24 18:15 +0200
                Re: "C++20 Coroutines" by Martin Bond Branimir Maksimovic <branimir.maksimovic@gmail.com> - 2021-09-25 00:57 +0000
                Re: "C++20 Coroutines" by Martin Bond HorseyWorsey@the_stables.com - 2021-09-23 09:11 +0000
                Re: "C++20 Coroutines" by Martin Bond Bonita Montero <Bonita.Montero@gmail.com> - 2021-09-24 18:17 +0200
                Re: "C++20 Coroutines" by Martin Bond HorseyWorsey@the_stables.com - 2021-09-25 09:19 +0000
                Re: "C++20 Coroutines" by Martin Bond Bonita Montero <Bonita.Montero@gmail.com> - 2021-09-25 12:00 +0200
                Re: "C++20 Coroutines" by Martin Bond HorseyWorsey@the_stables.com - 2021-09-25 10:09 +0000
                Re: "C++20 Coroutines" by Martin Bond Bonita Montero <Bonita.Montero@gmail.com> - 2021-09-25 12:18 +0200
                Re: "C++20 Coroutines" by Martin Bond HorseyWorsey@the_stables.com - 2021-09-25 10:39 +0000
                Re: "C++20 Coroutines" by Martin Bond Bonita Montero <Bonita.Montero@gmail.com> - 2021-09-25 12:42 +0200
                Re: "C++20 Coroutines" by Martin Bond HorseyWorsey@the_stables.com - 2021-09-25 10:44 +0000
                Re: "C++20 Coroutines" by Martin Bond Bonita Montero <Bonita.Montero@gmail.com> - 2021-09-25 13:14 +0200
                Re: "C++20 Coroutines" by Martin Bond Branimir Maksimovic <branimir.maksimovic@gmail.com> - 2021-09-25 12:44 +0000
                Re: "C++20 Coroutines" by Martin Bond Bonita Montero <Bonita.Montero@gmail.com> - 2021-09-25 15:58 +0200
                Re: "C++20 Coroutines" by Martin Bond Branimir Maksimovic <branimir.maksimovic@gmail.com> - 2021-09-25 13:59 +0000
                Re: "C++20 Coroutines" by Martin Bond Bonita Montero <Bonita.Montero@gmail.com> - 2021-09-25 16:23 +0200
                Re: "C++20 Coroutines" by Martin Bond Bonita Montero <Bonita.Montero@gmail.com> - 2021-09-28 07:24 +0200
                Re: "C++20 Coroutines" by Martin Bond HorseyWorsey@the_stables.com - 2021-09-25 15:28 +0000
                Re: "C++20 Coroutines" by Martin Bond HorseyWorsey@the_stables.com - 2021-09-25 15:04 +0000
                Re: "C++20 Coroutines" by Martin Bond Bonita Montero <Bonita.Montero@gmail.com> - 2021-09-25 18:44 +0200
                Re: "C++20 Coroutines" by Martin Bond HorseyWorsey@the_stables.com - 2021-09-26 14:15 +0000
                Re: "C++20 Coroutines" by Martin Bond Branimir Maksimovic <branimir.maksimovic@gmail.com> - 2021-09-25 12:32 +0000
          Re: "C++20 Coroutines" by Martin Bond Juha Nieminen <nospam@thanks.invalid> - 2021-09-23 07:42 +0000
            Re: "C++20 Coroutines" by Martin Bond HorseyWorsey@the_stables.com - 2021-09-23 09:14 +0000
              Re: "C++20 Coroutines" by Martin Bond Juha Nieminen <nospam@thanks.invalid> - 2021-09-24 04:42 +0000
            Re: "C++20 Coroutines" by Martin Bond Bonita Montero <Bonita.Montero@gmail.com> - 2021-09-24 18:19 +0200
              Re: "C++20 Coroutines" by Martin Bond Ben Bacarisse <ben.usenet@bsb.me.uk> - 2021-09-24 21:07 +0100
                Re: "C++20 Coroutines" by Martin Bond Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-10-06 13:19 -0700
              Re: "C++20 Coroutines" by Martin Bond Branimir Maksimovic <branimir.maksimovic@gmail.com> - 2021-09-25 00:58 +0000
                Re: "C++20 Coroutines" by Martin Bond Juha Nieminen <nospam@thanks.invalid> - 2021-09-27 05:39 +0000
                Re: "C++20 Coroutines" by Martin Bond Branimir Maksimovic <branimir.maksimovic@gmail.com> - 2021-09-29 02:30 +0000
              Re: "C++20 Coroutines" by Martin Bond HorseyWorsey@the_stables.com - 2021-09-25 09:20 +0000
        Re: "C++20 Coroutines" by Martin Bond "Alf P. Steinbach" <alf.p.steinbach@gmail.com> - 2021-09-22 11:31 +0200
      Re: "C++20 Coroutines" by Martin Bond Sam <sam@email-scan.com> - 2021-09-22 18:43 -0400
        Re: "C++20 Coroutines" by Martin Bond Juha Nieminen <nospam@thanks.invalid> - 2021-09-23 07:45 +0000
          Re: "C++20 Coroutines" by Martin Bond "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2021-09-23 01:53 -0700
          Re: "C++20 Coroutines" by Martin Bond Sam <sam@email-scan.com> - 2021-09-24 19:21 -0400
            Re: "C++20 Coroutines" by Martin Bond HorseyWorsey@the_stables.com - 2021-09-25 09:28 +0000
              Re: "C++20 Coroutines" by Martin Bond Branimir Maksimovic <branimir.maksimovic@gmail.com> - 2021-09-25 12:38 +0000
            Re: "C++20 Coroutines" by Martin Bond Juha Nieminen <nospam@thanks.invalid> - 2021-09-27 05:42 +0000
  Re: "C++20 Coroutines" by Martin Bond "Alf P. Steinbach" <alf.p.steinbach@gmail.com> - 2021-09-25 15:14 +0200
    Re: "C++20 Coroutines" by Martin Bond Manfred <noname@add.invalid> - 2021-09-25 23:07 +0200
      Re: "C++20 Coroutines" by Martin Bond "Alf P. Steinbach" <alf.p.steinbach@gmail.com> - 2021-09-26 01:50 +0200
        Re: "C++20 Coroutines" by Martin Bond Manfred <noname@add.invalid> - 2021-09-26 19:12 +0200

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