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Groups > comp.lang.c > #69959

Re: lalloc() -- local stack allocation

From Ben Bacarisse <ben.usenet@bsb.me.uk>
Newsgroups comp.lang.c
Subject Re: lalloc() -- local stack allocation
Date 2015-09-08 20:32 +0100
Organization A noiseless patient Spider
Message-ID <87fv2oogft.fsf@bsb.me.uk> (permalink)
References <e9abe69a-2532-44f3-be7b-aaa236783cfb@googlegroups.com> <fe75fd6a-a46e-42db-ac7c-3d9ab9fc8da0@googlegroups.com> <mntum4$pf0$1@news.albasani.net> <73cc6924-226c-4615-9d03-fc7f7a5e4667@googlegroups.com>

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supercat@casperkitty.com writes:

> On Sunday, July 12, 2015 at 9:47:45 AM UTC-5, Johannes Bauer wrote:
>> Which completely defies the purpose of using the system stack. Because
>> there you don't have to free because free is implicit at the end of a
>> function scope when the stackframe is cleared.
>
> A well-designed stack-allocate mechanism would have included a stack-free
> function and required that code must use it to free objects in the reverse
> order of allocation.  Such requirements would have meant that every platform
> that can run a reasonable dialect of C could support code using such
> functions merely by chaining them to "malloc" and "free", but platforms which
> can benefit from distinguishing between temporary and persistent objects
> could make use of that knowledge.  Even platforms would require that such
> objects be allocated on the heap rather than the CPU stack may be able to
> benefit from having separate functions for temporary allocations (e.g. by
> maintaining a pre-allocated area for such allocations which is separate from
> the main heap).
>
> The lack of a "free" function is bad in a number of ways:
>
> 1. It's incompatible with a pattern of "read size, allocate array, read and
>    process data, release array, read next size, etc." since memory that gets
>    stack-allocated within a method can't be freed.
>
> 2. On many platforms it makes it impossible to use a compatibility library
>    to allow code which is written to use alloca() to be run on a platforms
>    which doesn't include explicit support for it.
>
> 3. Unless a compiler adds some rather sophisticated alloca-related support,
>    it precludes the possibility of alloca() using a heap allocation rather
>    than a stack allocation in cases where stack memory is scarce.
>
> Having a function which allocates memory take care of releasing it isn't
> hard, and while I could see semantic benefit to having a compiler squawk if
> stack-allocate/stack-free calls aren't balanced, I don't see any upside to
> the implicit freeing of alloca() memory which are even remotely close to
> outweighing the drawbacks.

I'm not good at assessing advantages and drawbacks, but you can always
make yourself use such a language (in fact I have done so, knowing that
alloca is fast on some target systems and simply absent in others).
I.e. you write salloc and sfree which are either malloc and free or are
alloca and an empty stub.  It's not the same as having mandated features
of course, but I suspect its the kind of thing that is considered by
standards committees.  (And if I understand the intent, you don't get
number 3 as that's on the implementation side.)

-- 
Ben.

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lalloc() -- local stack allocation "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-07-12 02:23 -0700
  Re: lalloc() -- local stack allocation Johannes Bauer <dfnsonfsduifb@gmx.de> - 2015-07-12 11:48 +0200
    Re: lalloc() -- local stack allocation Johannes Bauer <dfnsonfsduifb@gmx.de> - 2015-07-12 11:48 +0200
  Re: lalloc() -- local stack allocation Philipp Klaus Krause <pkk@spth.de> - 2015-07-12 13:33 +0200
  Re: lalloc() -- local stack allocation Robert Wessel <robertwessel2@yahoo.com> - 2015-07-12 06:54 -0500
  Re: lalloc() -- local stack allocation Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-07-12 06:17 -0700
    Re: lalloc() -- local stack allocation Johannes Bauer <dfnsonfsduifb@gmx.de> - 2015-07-12 16:47 +0200
      Re: lalloc() -- local stack allocation Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-07-12 11:12 -0700
      Re: lalloc() -- local stack allocation supercat@casperkitty.com - 2015-09-08 11:53 -0700
        Re: lalloc() -- local stack allocation "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-09-08 12:16 -0700
          Re: lalloc() -- local stack allocation supercat@casperkitty.com - 2015-09-08 15:46 -0700
            Re: lalloc() -- local stack allocation "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-09-08 16:12 -0700
              Re: lalloc() -- local stack allocation supercat@casperkitty.com - 2015-09-09 06:53 -0700
                Re: lalloc() -- local stack allocation "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-09-09 16:06 -0700
                Re: lalloc() -- local stack allocation "Chris M. Thomasson" <nospam@nospam.nospam> - 2015-09-09 16:17 -0700
                Re: lalloc() -- local stack allocation "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-09-09 16:26 -0700
                Re: lalloc() -- local stack allocation "Chris M. Thomasson" <nospam@nospam.nospam> - 2015-09-09 19:22 -0700
                Re: lalloc() -- local stack allocation "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-09-09 19:55 -0700
                Re: lalloc() -- local stack allocation "Chris M. Thomasson" <nospam@nospam.nospam> - 2015-09-09 20:46 -0700
                Re: lalloc() -- local stack allocation "Chris M. Thomasson" <nospam@nospam.nospam> - 2015-09-09 20:50 -0700
                Re: lalloc() -- local stack allocation "Chris M. Thomasson" <nospam@nospam.nospam> - 2015-09-11 23:59 -0700
                Re: lalloc() -- local stack allocation "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-09-12 06:22 -0700
                Re: lalloc() -- local stack allocation "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-09-09 21:10 -0700
                Re: lalloc() -- local stack allocation supercat@casperkitty.com - 2015-09-10 07:08 -0700
                Re: lalloc() -- local stack allocation "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-09-10 08:17 -0700
                Re: lalloc() -- local stack allocation supercat@casperkitty.com - 2015-09-10 08:54 -0700
                Re: lalloc() -- local stack allocation "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-09-10 09:19 -0700
                Re: lalloc() -- local stack allocation supercat@casperkitty.com - 2015-09-10 16:55 -0700
                Re: lalloc() -- local stack allocation "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-09-10 18:41 -0700
                Re: lalloc() -- local stack allocation supercat@casperkitty.com - 2015-09-11 09:04 -0700
                Re: lalloc() -- local stack allocation "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-09-11 10:17 -0700
                Re: lalloc() -- local stack allocation supercat@casperkitty.com - 2015-09-11 11:34 -0700
                Re: lalloc() -- local stack allocation "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-09-11 11:47 -0700
                Re: lalloc() -- local stack allocation supercat@casperkitty.com - 2015-09-11 13:44 -0700
                Re: lalloc() -- local stack allocation "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-09-11 17:52 -0700
                Re: lalloc() -- local stack allocation "Chris M. Thomasson" <nospam@nospam.nospam> - 2015-09-11 11:37 -0700
                Re: lalloc() -- local stack allocation Richard Damon <Richard@Damon-Family.org> - 2015-09-10 08:24 -0400
                Re: lalloc() -- local stack allocation "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-09-10 05:55 -0700
                RDC (Was: lalloc() -- local stack allocation) gazelle@shell.xmission.com (Kenny McCormack) - 2015-09-10 13:01 +0000
                Re: lalloc() -- local stack allocation Richard Damon <Richard@Damon-Family.org> - 2015-09-11 00:29 -0400
                Re: lalloc() -- local stack allocation "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-09-11 05:37 -0700
                Re: lalloc() -- local stack allocation Richard Damon <Richard@Damon-Family.org> - 2015-09-11 22:48 -0400
                Re: lalloc() -- local stack allocation "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-09-11 20:05 -0700
                Re: lalloc() -- local stack allocation "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-09-11 20:22 -0700
                Re: lalloc() -- local stack allocation Melzzzzz <mel@zzzzz.com> - 2015-09-12 11:57 +0200
                Re: lalloc() -- local stack allocation fir <profesor.fir@gmail.com> - 2015-09-12 04:34 -0700
                Re: lalloc() -- local stack allocation fir <profesor.fir@gmail.com> - 2015-09-12 07:28 -0700
                Re: lalloc() -- local stack allocation "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-09-12 05:44 -0700
                Re: lalloc() -- local stack allocation Ian Collins <ian-news@hotmail.com> - 2015-09-12 13:02 +1200
                Re: lalloc() -- local stack allocation "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-09-11 18:25 -0700
                Re: lalloc() -- local stack allocation Ian Collins <ian-news@hotmail.com> - 2015-09-12 13:42 +1200
                Re: lalloc() -- local stack allocation "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-09-11 19:11 -0700
                Re: lalloc() -- local stack allocation Melzzzzz <mel@zzzzz.com> - 2015-09-12 04:27 +0200
                Re: lalloc() -- local stack allocation "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-09-11 19:44 -0700
                Re: lalloc() -- local stack allocation James Kuyper <jameskuyper@verizon.net> - 2015-09-11 23:01 -0400
                Re: lalloc() -- local stack allocation Richard Heathfield <rjh@cpax.org.uk> - 2015-09-12 11:12 +0100
                Re: lalloc() -- local stack allocation "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-09-12 05:55 -0700
                Re: lalloc() -- local stack allocation Richard Heathfield <rjh@cpax.org.uk> - 2015-09-12 14:16 +0100
                Re: lalloc() -- local stack allocation "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-09-12 06:24 -0700
                Re: lalloc() -- local stack allocation Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-09-12 10:57 -0700
                Re: lalloc() -- local stack allocation fir <profesor.fir@gmail.com> - 2015-09-12 11:13 -0700
                Re: lalloc() -- local stack allocation Gareth Owen <gwowen@gmail.com> - 2015-09-12 19:31 +0100
                Re: lalloc() -- local stack allocation gazelle@shell.xmission.com (Kenny McCormack) - 2015-09-12 19:20 +0000
                Re: lalloc() -- local stack allocation "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-09-12 12:06 -0700
                Re: lalloc() -- local stack allocation supercat@casperkitty.com - 2015-09-12 14:24 -0700
                Re: lalloc() -- local stack allocation "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-09-12 19:22 -0700
                Re: lalloc() -- local stack allocation Ian Collins <ian-news@hotmail.com> - 2015-09-12 14:54 +1200
                Re: lalloc() -- local stack allocation "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-09-11 20:18 -0700
                Re: lalloc() -- local stack allocation Ian Collins <ian-news@hotmail.com> - 2015-09-12 16:20 +1200
                Re: lalloc() -- local stack allocation "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-09-12 05:43 -0700
                Re: lalloc() -- local stack allocation "Chris M. Thomasson" <nospam@nospam.nospam> - 2015-09-12 14:02 -0700
                Re: lalloc() -- local stack allocation Melzzzzz <mel@zzzzz.com> - 2015-09-12 04:25 +0200
                Re: lalloc() -- local stack allocation Bartc <bc@freeuk.com> - 2015-09-12 10:32 +0100
                Re: lalloc() -- local stack allocation supercat@casperkitty.com - 2015-09-09 16:23 -0700
                Re: lalloc() -- local stack allocation "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-09-09 16:38 -0700
                Re: lalloc() -- local stack allocation supercat@casperkitty.com - 2015-09-09 17:01 -0700
                Re: lalloc() -- local stack allocation "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-09-09 17:08 -0700
                Re: lalloc() -- local stack allocation "Chris M. Thomasson" <nospam@nospam.nospam> - 2015-09-09 17:37 -0700
                Re: lalloc() -- local stack allocation "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-09-09 18:06 -0700
                Re: lalloc() -- local stack allocation Bartc <bc@freeuk.com> - 2015-09-10 10:54 +0100
                Re: lalloc() -- local stack allocation supercat@casperkitty.com - 2015-09-09 16:24 -0700
        Re: lalloc() -- local stack allocation Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-09-08 20:32 +0100
        Re: lalloc() -- local stack allocation jadill33@gmail.com - 2015-09-08 13:25 -0700
  Re: lalloc() -- local stack allocation "Chris M. Thomasson" <nospam@nospam.nospam> - 2015-07-12 10:17 -0700
  Re: lalloc() -- local stack allocation gordonb.zziiu@burditt.org (Gordon Burditt) - 2015-07-27 22:41 -0500
    Re: lalloc() -- local stack allocation Keith Thompson <kst-u@mib.org> - 2015-07-28 08:35 -0700

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