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Re: global/static variables & loops

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James Kuyper <jameskuyper@verizon.net> writes:

> On 02/15/2012 02:30 PM, Anders Wegge Keller wrote:

>>  If it quacks like a duck, walks like a duck and swims like a duck, it
>> probably is a duck, no matter how you dress it up. 
> 
> Well, that works both ways - labeling it a prejudice doesn't make it
> cease to be a well-justified judgment.

 Yoy have missed the point. I'm talking about cases like

 int debug_level;

 versus:

 static int debug_level
 int get_debug_level(void) { return debug_level; }
 void set_debug_level(int lvl) { debug_level = lvl; }

 I'm not trying to justify "All data should be global", as you seem to
imply. I'm questioning "No data should be global". There is a world
between those two statements.
 
>>  Scratch the getter/setter pattern, and the global struct pointer
>> that's passed down the call tree then. *OR* prototype the darn things
>> as const outside the translation unit that actually has to modify
>> them, and see where the compiler complains. (And remember to remove
>> the const prototype afterwards, unless you want to see some
>> spectacular failures :)
 
> I'm not sure what any of that word salad has to do with what I was
> talking about. Can you re-write it to make the relevance clearer?

 If my explanation above doesn't make it clearer, please ask
again. But I think we have two very different opinions about what
"state" actually means at present.

>>  Unless you have a very limited state space, that will lead to some
>> very convoluted and error-prone code. 
 
> Not in my experience.

 Try implementing GNU ls without globals. I know that the whole lot
are statics, since the code is in just one TU, but imagine something
of a similar magnitude then. The first few levels of functions will
have prototypes of several pages.

>>  You should try to do real-time machine control with 10-15
>> co-concurrent tasks running on a 80186 platform, where each
>> individual thread has a stack in the range 128 to 256 bytes, and
>> avoid overdoing need-to-know :) I'm in the 0.1%, where overdoing
>> things are a real-world problem.
 
> Limited stack space is something I've little recent experience with,
> but I agree that it's an excellent reason to avoid using the stack;
> in extreme cases, even passing pointers on the stack becomes
> problematic - but you should rarely need to go all the way to global
> visibility to avoid that problem. You have a greater need to use
> objects with static storage duration than I do, but you don't have
> to make every single one of them globally visible. I've a number of
> such objects in my own code.  Most of them have block scope, a few
> have file scope - but none has external linkage.

 When data is shared between several threads, and each thread live in
its own translation unit, that cannot be helped. The central part is
an array-esque (80186 memory model limitations) representation of
system state. Most manipulation happens through a set of state-event
machines, each doing their part. 

 And mind, this is hardware that was state of the art in the late
1980's, and we have been stuck on that ever since, because it works
too good to warrant a major architecture rewrite.

-- 
/Wegge

Leder efter redundant peering af dk.*,linux.debian.*

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global/static variables & loops Rob Janecek <robs@invalid.com> - 2012-02-14 19:56 +0000
  Re: global/static variables & loops Malcolm McLean <malcolm.mclean5@btinternet.com> - 2012-02-14 12:42 -0800
  Re: global/static variables & loops Stephen Sprunk <stephen@sprunk.org> - 2012-02-14 15:01 -0600
  Re: global/static variables & loops Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-02-14 20:35 -0500
    Re: global/static variables & loops Philip Lantz <prl@canterey.us> - 2012-02-14 21:18 -0800
    Re: global/static variables & loops pete <pfiland@mindspring.com> - 2012-02-15 00:53 -0500
      Re: global/static variables & loops Jonathan Leffler <jleffler@earthlink.net> - 2012-02-18 21:15 -0800
        Re: global/static variables & loops Kaz Kylheku <kaz@kylheku.com> - 2012-02-19 06:05 +0000
          Re: global/static variables & loops Phil Carmody <thefatphil_demunged@yahoo.co.uk> - 2012-02-22 03:15 +0200
        Re: global/static variables & loops Shao Miller <sha0.miller@gmail.com> - 2012-02-19 04:14 -0500
          Re: global/static variables & loops Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-02-19 12:32 +0000
            Re: Array 'typedef's and exclusive use of '->' versus '.' Shao Miller <sha0.miller@gmail.com> - 2012-02-19 17:00 -0500
              Re: Array 'typedef's and exclusive use of '->' versus '.' Keith Thompson <kst-u@mib.org> - 2012-02-19 16:43 -0800
                Re: Array 'typedef's and exclusive use of '->' versus '.' Shao Miller <sha0.miller@gmail.com> - 2012-02-19 20:32 -0500
              Re: Array 'typedef's and exclusive use of '->' versus '.' Phil Carmody <thefatphil_demunged@yahoo.co.uk> - 2012-02-22 03:27 +0200
                Re: Array 'typedef's and exclusive use of '->' versus '.' Shao Miller <sha0.miller@gmail.com> - 2012-02-25 02:19 -0500
                Re: Array 'typedef's and exclusive use of '->' versus '.' Phil Carmody <thefatphil_demunged@yahoo.co.uk> - 2012-02-25 10:14 +0200
    Re: global/static variables & loops "BartC" <bc@freeuk.com> - 2012-02-15 10:47 +0000
      Re: global/static variables & loops Kaz Kylheku <kaz@kylheku.com> - 2012-02-15 11:42 +0000
        Re: global/static variables & loops "BartC" <bc@freeuk.com> - 2012-02-15 12:54 +0000
        Re: global/static variables & loops Malcolm McLean <malcolm.mclean5@btinternet.com> - 2012-02-15 05:17 -0800
      Re: global/static variables & loops Phil Carmody <thefatphil_demunged@yahoo.co.uk> - 2012-02-22 03:28 +0200
    Re: global/static variables & loops August Karlstrom <fusionfile@gmail.com> - 2012-02-15 15:19 +0100
    Re: global/static variables & loops Phil Carmody <thefatphil_demunged@yahoo.co.uk> - 2012-02-22 03:12 +0200
  Re: global/static variables & loops Nick Keighley <nick_keighley_nospam@hotmail.com> - 2012-02-15 01:23 -0800
    Re: global/static variables & loops August Karlstrom <fusionfile@gmail.com> - 2012-02-15 14:03 +0100
      Re: global/static variables & loops Malcolm McLean <malcolm.mclean5@btinternet.com> - 2012-02-15 05:20 -0800
        Re: global/static variables & loops James Kuyper <jameskuyper@verizon.net> - 2012-02-15 08:41 -0500
          Re: global/static variables & loops Kaz Kylheku <kaz@kylheku.com> - 2012-02-16 00:20 +0000
            Re: global/static variables & loops Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-02-15 21:02 -0500
              Re: global/static variables & loops "BartC" <bc@freeuk.com> - 2012-02-16 10:03 +0000
                Re: global/static variables & loops Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-02-16 07:58 -0500
              Re: global/static variables & loops Markus Wichmann <nullplan@gmx.net> - 2012-02-19 20:44 +0100
                Re: global/static variables & loops Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-02-19 15:37 -0500
                Re: global/static variables & loops Kaz Kylheku <kaz@kylheku.com> - 2012-02-22 05:01 +0000
                Re: global/static variables & loops Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-02-22 08:12 -0500
    Re: global/static variables & loops Anders Wegge Keller <wegge@wegge.dk> - 2012-02-15 15:55 +0100
      Re: global/static variables & loops James Kuyper <jameskuyper@verizon.net> - 2012-02-15 11:05 -0500
      Re: global/static variables & loops Malcolm McLean <malcolm.mclean5@btinternet.com> - 2012-02-15 09:13 -0800
        Re: global/static variables & loops Anders Wegge Keller <wegge@wegge.dk> - 2012-02-15 18:25 +0100
          Re: global/static variables & loops James Kuyper <jameskuyper@verizon.net> - 2012-02-15 13:25 -0500
            Re: global/static variables & loops Malcolm McLean <malcolm.mclean5@btinternet.com> - 2012-02-15 10:51 -0800
              Re: global/static variables & loops James Kuyper <jameskuyper@verizon.net> - 2012-02-15 14:45 -0500
              Re: global/static variables & loops Anders Wegge Keller <wegge@wegge.dk> - 2012-02-15 20:47 +0100
                Re: global/static variables & loops Nick Keighley <nick_keighley_nospam@hotmail.com> - 2012-02-16 04:45 -0800
                Re: global/static variables & loops Anders Wegge Keller <wegge@wegge.dk> - 2012-02-16 14:25 +0100
                Re: global/static variables & loops Malcolm McLean <malcolm.mclean5@btinternet.com> - 2012-02-16 08:10 -0800
                Re: global/static variables & loops Nick Keighley <nick_keighley_nospam@hotmail.com> - 2012-02-17 00:59 -0800
            Re: global/static variables & loops Anders Wegge Keller <wegge@wegge.dk> - 2012-02-15 20:30 +0100
              Re: global/static variables & loops James Kuyper <jameskuyper@verizon.net> - 2012-02-15 15:00 -0500
                Re: global/static variables & loops Anders Wegge Keller <wegge@wegge.dk> - 2012-02-15 21:30 +0100
                Re: global/static variables & loops James Kuyper <jameskuyper@verizon.net> - 2012-02-15 16:00 -0500
                Re: global/static variables & loops Anders Wegge Keller <wegge@wegge.dk> - 2012-02-15 23:10 +0100
                Re: global/static variables & loops Malcolm McLean <malcolm.mclean5@btinternet.com> - 2012-02-15 15:50 -0800
                Re: global/static variables & loops James Kuyper <jameskuyper@verizon.net> - 2012-02-15 19:50 -0500
                Re: global/static variables & loops Anders Wegge Keller <wegge@wegge.dk> - 2012-02-16 14:36 +0100
            Re: global/static variables & loops Nick Keighley <nick_keighley_nospam@hotmail.com> - 2012-02-16 03:29 -0800
      Re: global/static variables & loops Anders Wegge Keller <wegge@wegge.dk> - 2012-02-15 23:37 +0100
      Re: global/static variables & loops Kaz Kylheku <kaz@kylheku.com> - 2012-02-16 00:23 +0000
        Re: global/static variables & loops Anders Wegge Keller <wegge@wegge.dk> - 2012-02-16 01:29 +0100
        Re: global/static variables & loops Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-02-15 21:20 -0500
      Re: global/static variables & loops Shao Miller <sha0.miller@gmail.com> - 2012-02-15 22:24 -0500
        Re: global/static variables & loops Malcolm McLean <malcolm.mclean5@btinternet.com> - 2012-02-16 01:08 -0800
      Re: global/static variables & loops Nick Keighley <nick_keighley_nospam@hotmail.com> - 2012-02-16 03:17 -0800

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