Re: Why can't I understand what coroutines are?

From	"Alf P. Steinbach" <alf.p.steinbach+usenet@gmail.com>
Newsgroups	comp.lang.c++
Subject	Re: Why can't I understand what coroutines are?
Date	2019-08-05 01:11 +0200
Organization	A noiseless patient Spider
Message-ID	<qi7omo$v95$1@dont-email.me> (permalink)
References	<qi6910$1eht$1@adenine.netfront.net>

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On 04.08.2019 11:37, Juha Nieminen wrote:
> C++20 will introduce support for coroutines. To this day, for reasons
> that are completely mysterious even to me, I have *absolutely no idea*
> what they are. I just don't get it.
> 
> I go to the Wikipedia page "Coroutine"... and it tells me nothing.

[snip]

I'll address the conceptual only.

When I saw this posting earlier today I thought I'd whip up a concrete 
example, like I implemented coroutines in the mid 1990's. However, I 
discovered that I would then be late for a dinner, so I put it on hold.

Coroutines are just cooperative multitasking, multitasking with a single 
thread of execution but multiple call stacks. When you CALL a coroutine 
you create a new instance, with its own stack. There is nothing like 
that in the standard library. When a coroutine TRANSFERs to another 
coroutine it's like a `longjmp`, except that `longjmp` was designed to 
jump up to an earlier point in a call chain, while a coroutine transfer 
jumps to a separate call chain.

As I recall you're familiar with 16-bit Windows programming.

In 16-bit Windows (Windows 3.x in the early 1990s) each program 
execution was a coroutine. When a program was launched, a stack area was 
allocated for it. That's a call of a coroutine. When the program called 
`GetMessage` or `Yield`, some other program instance would get a chance 
to continue to run (after waiting for /its/ call to `GetMessage` or 
`Yield` to return). That's a coroutine transfer.

The 16-bit Windows program execution were /huge/, heavy coroutines.

However, the main advantage of coroutines in ordinary programming is 
with coroutines as a very light-weight multitasking solution. Since 
there's only one thread of execution there are fewer synchronization 
issues. In particular one doesn't have to worry about whether one 
coroutine sees the memory changes effected by some other coroutine.

Cheers & hht.,

- Alf

Thread

Why can't I understand what coroutines are? Juha Nieminen <nospam@thanks.invalid> - 2019-08-04 09:37 +0000
  Re: Why can't I understand what coroutines are? "Chris M. Thomasson" <invalid_chris_thomasson_invalid@invalid.com> - 2019-08-04 02:58 -0700
    Re: Why can't I understand what coroutines are? Sam <sam@email-scan.com> - 2019-08-04 09:18 -0400
      Re: Why can't I understand what coroutines are? "Chris M. Thomasson" <invalid_chris_thomasson_invalid@invalid.com> - 2019-08-04 11:15 -0700
  Re: Why can't I understand what coroutines are? Louis Krupp <lkrupp@nospam.pssw.com.invalid> - 2019-08-04 04:58 -0600
    Re: Why can't I understand what coroutines are? Juha Nieminen <nospam@thanks.invalid> - 2019-08-05 08:31 +0000
      Re: Why can't I understand what coroutines are? Martijn van Buul <pino@dohd.org> - 2019-08-05 09:51 +0000
        Re: Why can't I understand what coroutines are? "Chris M. Thomasson" <invalid_chris_thomasson_invalid@invalid.com> - 2019-08-05 14:44 -0700
  Re: Why can't I understand what coroutines are? Chris Vine <chris@cvine--nospam--.freeserve.co.uk> - 2019-08-04 14:08 +0100
    Re: Why can't I understand what coroutines are? Sam <sam@email-scan.com> - 2019-08-04 09:23 -0400
      Re: Why can't I understand what coroutines are? Chris Vine <chris@cvine--nospam--.freeserve.co.uk> - 2019-08-04 14:36 +0100
        Re: Why can't I understand what coroutines are? Sam <sam@email-scan.com> - 2019-08-04 10:31 -0400
          Re: Why can't I understand what coroutines are? Chris Vine <chris@cvine--nospam--.freeserve.co.uk> - 2019-08-04 16:42 +0100
            Re: Why can't I understand what coroutines are? Sam <sam@email-scan.com> - 2019-08-04 16:43 -0400
              Re: Why can't I understand what coroutines are? "Chris M. Thomasson" <invalid_chris_thomasson_invalid@invalid.com> - 2019-08-04 13:58 -0700
                Re: Why can't I understand what coroutines are? Sam <sam@email-scan.com> - 2019-08-04 17:36 -0400
                Re: Why can't I understand what coroutines are? Mr Flibble <flibbleREMOVETHISBIT@i42.co.uk> - 2019-08-04 22:43 +0100
                Re: Why can't I understand what coroutines are? Chris Vine <chris@cvine--nospam--.freeserve.co.uk> - 2019-08-04 22:52 +0100
                Re: Why can't I understand what coroutines are? Mr Flibble <flibbleREMOVETHISBIT@i42.co.uk> - 2019-08-04 23:10 +0100
                Re: Why can't I understand what coroutines are? Sam <sam@email-scan.com> - 2019-08-04 21:32 -0400
                Re: Why can't I understand what coroutines are? Mr Flibble <flibbleREMOVETHISBIT@i42.co.uk> - 2019-08-05 18:32 +0100
                Re: Why can't I understand what coroutines are? scott@slp53.sl.home (Scott Lurndal) - 2019-08-05 17:48 +0000
                Re: Why can't I understand what coroutines are? Sam <sam@email-scan.com> - 2019-08-05 20:14 -0400
                Re: Why can't I understand what coroutines are? leigh.v.johnston@googlemail.com - 2019-08-06 04:13 -0700
                Re: Why can't I understand what coroutines are? leigh.v.johnston@googlemail.com - 2019-08-06 04:23 -0700
                Re: Why can't I understand what coroutines are? Chris Vine <chris@cvine--nospam--.freeserve.co.uk> - 2019-08-06 22:19 +0100
                Re: Why can't I understand what coroutines are? "Chris M. Thomasson" <invalid_chris_thomasson_invalid@invalid.com> - 2019-08-06 15:19 -0700
                Re: Why can't I understand what coroutines are? Chris Vine <chris@cvine--nospam--.freeserve.co.uk> - 2019-08-07 00:01 +0100
                Re: Why can't I understand what coroutines are? scott@slp53.sl.home (Scott Lurndal) - 2019-08-06 23:52 +0000
                Re: Why can't I understand what coroutines are? Öö Tiib <ootiib@hot.ee> - 2019-08-06 16:57 -0700
                Re: Why can't I understand what coroutines are? scott@slp53.sl.home (Scott Lurndal) - 2019-08-07 14:41 +0000
                Re: Why can't I understand what coroutines are? Öö Tiib <ootiib@hot.ee> - 2019-08-08 07:10 -0700
                Re: Why can't I understand what coroutines are? scott@slp53.sl.home (Scott Lurndal) - 2019-08-06 23:49 +0000
                Re: Why can't I understand what coroutines are? Robert Wessel <robertwessel2@yahoo.com> - 2019-08-04 22:04 -0500
                Re: Why can't I understand what coroutines are? "Chris M. Thomasson" <invalid_chris_thomasson_invalid@invalid.com> - 2019-08-04 20:10 -0700
        Re: Why can't I understand what coroutines are? "Chris M. Thomasson" <invalid_chris_thomasson_invalid@invalid.com> - 2019-08-04 11:20 -0700
          Re: Why can't I understand what coroutines are? Chris Vine <chris@cvine--nospam--.freeserve.co.uk> - 2019-08-04 20:30 +0100
            Re: Why can't I understand what coroutines are? "Chris M. Thomasson" <invalid_chris_thomasson_invalid@invalid.com> - 2019-08-04 14:03 -0700
            Re: Why can't I understand what coroutines are? Paavo Helde <myfirstname@osa.pri.ee> - 2019-08-05 09:36 +0300
              Re: Why can't I understand what coroutines are? "Chris M. Thomasson" <invalid_chris_thomasson_invalid@invalid.com> - 2019-08-05 14:34 -0700
        Re: Why can't I understand what coroutines are? scott@slp53.sl.home (Scott Lurndal) - 2019-08-04 19:46 +0000
      Re: Why can't I understand what coroutines are? Juha Nieminen <nospam@thanks.invalid> - 2019-08-05 08:37 +0000
        Re: Why can't I understand what coroutines are? David Brown <david.brown@hesbynett.no> - 2019-08-05 12:06 +0200
          Re: Why can't I understand what coroutines are? Juha Nieminen <nospam@thanks.invalid> - 2019-08-05 12:20 +0000
            Re: Why can't I understand what coroutines are? David Brown <david.brown@hesbynett.no> - 2019-08-06 15:06 +0200
              Re: Why can't I understand what coroutines are? David Brown <david.brown@hesbynett.no> - 2019-08-06 15:18 +0200
          Re: Why can't I understand what coroutines are? Bonita Montero <Bonita.Montero@gmail.com> - 2019-08-06 13:58 +0200
  Re: Why can't I understand what coroutines are? Sam <sam@email-scan.com> - 2019-08-04 09:17 -0400
  Re: Why can't I understand what coroutines are? Robert Wessel <robertwessel2@yahoo.com> - 2019-08-04 10:12 -0500
    Re: Why can't I understand what coroutines are? Juha Nieminen <nospam@thanks.invalid> - 2019-08-05 08:42 +0000
      Re: Why can't I understand what coroutines are? Chris Vine <chris@cvine--nospam--.freeserve.co.uk> - 2019-08-05 13:35 +0100
      Re: Why can't I understand what coroutines are? Bart <bc@freeuk.com> - 2019-08-05 20:19 +0100
      Re: Why can't I understand what coroutines are? Christian Gollwitzer <auriocus@gmx.de> - 2019-08-05 22:26 +0200
        Re: Why can't I understand what coroutines are? "Alf P. Steinbach" <alf.p.steinbach+usenet@gmail.com> - 2019-08-05 23:09 +0200
          Re: Why can't I understand what coroutines are? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2019-08-09 19:49 -0700
            Re: Why can't I understand what coroutines are? "Alf P. Steinbach" <alf.p.steinbach+usenet@gmail.com> - 2019-08-10 05:13 +0200
          Re: Why can't I understand what coroutines are? Christian Gollwitzer <auriocus@gmx.de> - 2019-08-10 08:23 +0200
            Re: Why can't I understand what coroutines are? "Alf P. Steinbach" <alf.p.steinbach+usenet@gmail.com> - 2019-08-10 10:43 +0200
              Re: Why can't I understand what coroutines are? Christian Gollwitzer <auriocus@gmx.de> - 2019-08-11 22:19 +0200
                Re: Why can't I understand what coroutines are? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2019-08-14 08:25 -0700
        Re: Why can't I understand what coroutines are? "Chris M. Thomasson" <invalid_chris_thomasson_invalid@invalid.com> - 2019-08-10 00:19 -0700
        Re: Why can't I understand what coroutines are? Juha Nieminen <nospam@thanks.invalid> - 2019-08-11 21:16 +0000
      Re: Why can't I understand what coroutines are? "Chris M. Thomasson" <invalid_chris_thomasson_invalid@invalid.com> - 2019-08-05 23:43 -0700
      Re: Why can't I understand what coroutines are? Bonita Montero <Bonita.Montero@gmail.com> - 2019-08-10 10:50 +0200
  Re: Why can't I understand what coroutines are? Mr Flibble <flibbleREMOVETHISBIT@i42.co.uk> - 2019-08-04 17:57 +0100
  Re: Why can't I understand what coroutines are? "Alf P. Steinbach" <alf.p.steinbach+usenet@gmail.com> - 2019-08-05 01:11 +0200
    Re: Why can't I understand what coroutines are? Juha Nieminen <nospam@thanks.invalid> - 2019-08-05 08:50 +0000
      Re: Why can't I understand what coroutines are? "Alf P. Steinbach" <alf.p.steinbach+usenet@gmail.com> - 2019-08-05 16:59 +0200
    Re: Why can't I understand what coroutines are? Manfred <noname@add.invalid> - 2019-08-06 16:24 +0200
    Re: Why can't I understand what coroutines are? "Alf P. Steinbach" <alf.p.steinbach+usenet@gmail.com> - 2019-08-07 00:52 +0200
      Re: Why can't I understand what coroutines are? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2019-08-09 18:11 -0700
  Re: Why can't I understand what coroutines are? Martijn van Buul <pino@dohd.org> - 2019-08-05 07:46 +0000

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