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

From	"Chris M. Thomasson" <invalid_chris_thomasson_invalid@invalid.com>
Newsgroups	comp.lang.c++
Subject	Re: Why can't I understand what coroutines are?
Date	2019-08-04 14:03 -0700
Organization	Aioe.org NNTP Server
Message-ID	<qi7h6t$eud$1@gioia.aioe.org> (permalink)
References	(1 earlier) <20190804140857.f1a22df42a76938b234edf4b@cvine--nospam--.freeserve.co.uk> <cone.1564925032.455203.25830.1004@monster.email-scan.com> <20190804143647.511134ccbc3ef6771a692cf7@cvine--nospam--.freeserve.co.uk> <qi77m2$13kh$1@gioia.aioe.org> <20190804203030.9a065d398363744cae8888b0@cvine--nospam--.freeserve.co.uk>

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On 8/4/2019 12:30 PM, Chris Vine wrote:
> On Sun, 4 Aug 2019 11:20:51 -0700
> "Chris M. Thomasson" <invalid_chris_thomasson_invalid@invalid.com>
> wrote:
>> On 8/4/2019 6:36 AM, Chris Vine wrote:
>>> On Sun, 04 Aug 2019 09:23:52 -0400
>>> Sam <sam@email-scan.com> wrote:
>>>> Chris Vine writes:
>>>>
>>>>> Asynchronous programming with callbacks normally works so that when a
>>>>> i/o operation might block because the resource in question (read or
>>>>> write) is unavailable, instead of blocking the function returns
>>>>> immediately and registers a callback with the program's event loop
>>>>> (usually based on select() or poll()), representing the i/o operation's
>>>>> continuation when the resource becomes available.  Programming this way
>>>>> using callbacks in the style of, say, Node.js is troublesome because it
>>>>> gives rise to what is sometimes called inversion of control, aka
>>>>> "callback hell".  In particular, control flow ceases to appear as a
>>>>> sequential series of i/o operations which can easily be reasoned about.
>>>>
>>>> This problem was solved a long time ago. It is called "threads".
>>>>
>>>> The funniest thing about this is that Gnome is most extreme case of this.
>>>> The entire Gnome stack is just one event dispatching main loop. Everything
>>>> is callbacks. But since Gnome is C code, none of this will help it, that's
>>>> the funny part.
>>>
>>> Threads are very definitely not the answer.  Threads work well with
>>> cpu-bound workloads.  They are hopeless with i/o-bound workloads, which
>>> is why co-operative (possibly single-threaded) multi-tasking using
>>> coroutines has become popular.
>>>
>>> If you use native OS threads for i/o bound workloads, you are doing it
>>> wrong.
>>>
>>
>> Threads can work fairly well with IO, take a look at IOCP:
>>
>> https://docs.microsoft.com/en-us/windows/win32/fileio/i-o-completion-ports
> 
> I don't know microsoft's implementations, but as far as I can make out
> the i/o is still done asynchronously (the file operations themselves do
> not block) but when an asynchronous operation completes that completion
> is handled by the completion port.  Although threads can wait on the
> completion port for an i/o operation to reach completion, there appears
> to be some form of multiplexing so that one thread can handle a number
> of completions, and the documentation suggests that having a number of
> threads equal to the number of cores (as opposed to the number of
> connections) as a good starting point, which seems reasonable.
> 
> But I cannot say the documentation you refer to is that clear: is my
> summary wrong (and if so, what's the point of completion ports in the
> first place)?  I find it hard to believe microsoft would have gone for
> the one thread per connection option favoured by my respondent.
> 

You treat each connection as a little state machine. This state has a 
socket, file, whatever, along with a memory buffer, or a pointer into 
some memory for io. It gets associated with the IOCP. Create several 
worker threads, one or two per CPU, and set the concurrency level to the 
number of CPUs. Now, worker threads wait on the IOCP for events. Each 
event has the state of the connection. If a read event fires, the memory 
buffer has the data, or there might be an error, whatever.

Actually, imvho, creating servers with IOCP is fairly straightforward.

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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