Re: realloc() - frequency, conditions, or experiences about relocation?

From	Keith Thompson <Keith.S.Thompson+u@gmail.com>
Newsgroups	comp.lang.c
Subject	Re: realloc() - frequency, conditions, or experiences about relocation?
Date	2024-06-17 16:39 -0700
Organization	None to speak of
Message-ID	<87h6dr16md.fsf@nosuchdomain.example.com> (permalink)
References	<v4ojs8$gvji$1@dont-email.me> <875xu8vsen.fsf@bsb.me.uk> <v4ovqf$j5hq$1@dont-email.me> <87zfrjvqp6.fsf@bsb.me.uk> <v4pb4v$lhgk$1@dont-email.me>

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Malcolm McLean <malcolm.arthur.mclean@gmail.com> writes:
[...]
> We have a continuously growing buffer, and we want the best strategy
> for reallocations as the stream of characters comes at us. So, given
> we now how many characters have arrived, can we predict how many will
> arrive, and therefore ask for the best amount when we reallocate, so
> that we neither make too many reallocation (reallocate on every byte
> received) or ask for too much (demand SIZE_MAX memory when the first
> byte is received).?
[...]

That's going to depend on the behavior of the implementations
realloc() function.

malloc() and realloc() typically allocate more memory than they're
asked for, so that another realloc() call can often expand the
allocated memory in place.

I have a small test program that uses realloc() to expand a 1-byte
allocated buffer to 2 bytes, then 3, then 4, and so on.  In one
implementation, in one test run, it reallocates at 25 bytes, and
then not again until just over 128 kbytes.  Other implementations
behave differently.

A realloc() call that's able to return its first argument is likely
to be much quicker than one that does an actual reallocation.
If you want to fine tune for performance, you'll have to allow
for the implementation you're using, either by performing run-time
measurements or by analyzing the implementation (which could change
in the next release).

Multiplying the size by 2 or 1.5 as needed is likely to be good enough.

-- 
Keith Thompson (The_Other_Keith) Keith.S.Thompson+u@gmail.com
void Void(void) { Void(); } /* The recursive call of the void */

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realloc() - frequency, conditions, or experiences about relocation? Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2024-06-17 08:08 +0200
  Re: realloc() - frequency, conditions, or experiences about relocation? "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-06-16 23:34 -0700
  Re: realloc() - frequency, conditions, or experiences about relocation? Ben Bacarisse <ben@bsb.me.uk> - 2024-06-17 10:18 +0100
    Re: realloc() - frequency, conditions, or experiences about relocation? Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2024-06-17 10:31 +0100
      Re: realloc() - frequency, conditions, or experiences about relocation? Ben Bacarisse <ben@bsb.me.uk> - 2024-06-17 10:55 +0100
        Re: realloc() - frequency, conditions, or experiences about relocation? Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2024-06-17 13:45 +0100
          Re: realloc() - frequency, conditions, or experiences about relocation? Ben Bacarisse <ben@bsb.me.uk> - 2024-06-17 15:33 +0100
            Re: realloc() - frequency, conditions, or experiences about relocation? Anton Shepelev <anton.txt@g{oogle}mail.com> - 2024-06-17 18:10 +0300
              Re: realloc() - frequency, conditions, or experiences about relocation? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2024-06-18 00:09 -0700
                Re: realloc() - frequency, conditions, or experiences about relocation? Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2024-06-18 11:19 +0100
                Re: realloc() - frequency, conditions, or experiences about relocation? Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2024-06-18 11:46 +0100
                Re: realloc() - frequency, conditions, or experiences about relocation? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2024-06-24 09:32 -0700
                Re: realloc() - frequency, conditions, or experiences about relocation? David Brown <david.brown@hesbynett.no> - 2024-06-24 19:19 +0200
                Indefinite pronouns [was:Re: realloc() - frequency, conditions, or experiences about relocation?] Anton Shepelev <anton.txt@gmail.moc> - 2024-06-20 02:51 +0300
                Re: Indefinite pronouns vallor <vallor@cultnix.org> - 2024-06-20 00:34 +0000
                Re: Indefinite pronouns David Brown <david.brown@hesbynett.no> - 2024-06-21 12:59 +0200
                Re: Indefinite pronouns Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-06-21 10:31 -0700
                Re: Indefinite pronouns [was:Re: realloc() - frequency, conditions, or experiences about relocation?] gazelle@shell.xmission.com (Kenny McCormack) - 2024-06-20 12:10 +0000
                Re: Indefinite pronouns [was: Re: <something technical>] Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2024-06-20 15:04 +0200
                Re: Indefinite pronouns [was:Re: realloc() - frequency, conditions, or experiences about relocation?] Cri-Cri <cri@cri.cri.invalid> - 2024-06-21 00:55 +0000
                Re: Indefinite pronouns [was:Re: realloc() - frequency, conditions, or experiences about relocation?] Tim Rentsch <tr.17687@z991.linuxsc.com> - 2024-06-20 23:23 -0700
            Re: realloc() - frequency, conditions, or experiences about relocation? Richard Harnden <richard.nospam@gmail.invalid> - 2024-06-17 16:15 +0100
              Re: realloc() - frequency, conditions, or experiences about relocation? "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-06-17 13:05 -0700
            Re: realloc() - frequency, conditions, or experiences about relocation? Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2024-06-17 16:36 +0100
          Re: realloc() - frequency, conditions, or experiences about relocation? Anton Shepelev <anton.txt@g{oogle}mail.com> - 2024-06-17 18:02 +0300
            Re: realloc() - frequency, conditions, or experiences about relocation? "David Jones" <dajhawk18xx@@nowhere.com> - 2024-06-18 17:59 +0000
            Re: realloc() - frequency, conditions, or experiences about relocation? davidd02@tpg.com.au (David Duffy) - 2024-06-19 06:48 +0000
              Re: realloc() - frequency, conditions, or experiences about relocation? Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2024-06-19 10:12 +0100
                Re: realloc() - frequency, conditions, or experiences about relocation? Ben Bacarisse <ben@bsb.me.uk> - 2024-06-19 16:36 +0100
                Re: realloc() - frequency, conditions, or experiences about relocation? David Brown <david.brown@hesbynett.no> - 2024-06-19 19:41 +0200
                Re: realloc() - frequency, conditions, or experiences about relocation? Ben Bacarisse <ben@bsb.me.uk> - 2024-06-19 22:24 +0100
                Re: realloc() - frequency, conditions, or experiences about relocation? David Brown <david.brown@hesbynett.no> - 2024-06-20 13:22 +0200
                Re: realloc() - frequency, conditions, or experiences about relocation? Anton Shepelev <anton.txt@gmail.moc> - 2024-06-20 01:53 +0300
              Re: realloc() - frequency, conditions, or experiences about relocation? Anton Shepelev <anton.txt@g{oogle}mail.com> - 2024-06-19 15:20 +0300
          Re: realloc() - frequency, conditions, or experiences about relocation? scott@slp53.sl.home (Scott Lurndal) - 2024-06-17 16:58 +0000
            Re: realloc() - frequency, conditions, or experiences about relocation? "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-06-17 13:12 -0700
          Re: realloc() - frequency, conditions, or experiences about relocation? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-06-17 16:39 -0700
            Re: realloc() - frequency, conditions, or experiences about relocation? Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2024-06-18 06:12 +0100
            Re: realloc() - frequency, conditions, or experiences about relocation? Bonita Montero <Bonita.Montero@gmail.com> - 2024-06-18 09:56 +0200
      Re: realloc() - frequency, conditions, or experiences about relocation? David Brown <david.brown@hesbynett.no> - 2024-06-17 20:11 +0200
  Re: realloc() - frequency, conditions, or experiences about relocation? Bonita Montero <Bonita.Montero@gmail.com> - 2024-06-17 11:22 +0200
    Re: realloc() - frequency, conditions, or experiences about relocation? Vir Campestris <vir.campestris@invalid.invalid> - 2024-06-20 21:08 +0100
      Re: realloc() - frequency, conditions, or experiences about relocation? Bonita Montero <Bonita.Montero@gmail.com> - 2024-06-21 21:12 +0200
        Re: realloc() - frequency, conditions, or experiences about relocation? Lawrence D'Oliveiro <ldo@nz.invalid> - 2024-06-24 08:40 +0000
          Re: realloc() - frequency, conditions, or experiences about relocation? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-06-24 02:55 -0700
            Re: realloc() - frequency, conditions, or experiences about relocation? David Brown <david.brown@hesbynett.no> - 2024-06-24 13:40 +0200
              Re: realloc() - frequency, conditions, or experiences about relocation? Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2024-06-24 18:50 +0100
                Re: realloc() - frequency, conditions, or experiences about relocation? scott@slp53.sl.home (Scott Lurndal) - 2024-06-24 18:20 +0000
                Re: realloc() - frequency, conditions, or experiences about relocation? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-06-24 14:28 -0700
                Re: realloc() - frequency, conditions, or experiences about relocation? Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2024-06-25 00:22 +0100
                Re: realloc() - frequency, conditions, or experiences about relocation? "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-06-24 18:31 -0700
                Re: realloc() - frequency, conditions, or experiences about relocation? Lawrence D'Oliveiro <ldo@nz.invalid> - 2024-06-25 07:06 +0000
                Re: realloc() - frequency, conditions, or experiences about relocation? Bonita Montero <Bonita.Montero@gmail.com> - 2024-06-25 10:38 +0200
                Re: realloc() - frequency, conditions, or experiences about relocation? Lawrence D'Oliveiro <ldo@nz.invalid> - 2024-06-26 00:51 +0000
              Re: realloc() - frequency, conditions, or experiences about relocation? "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-06-24 12:33 -0700
                Re: realloc() - frequency, conditions, or experiences about relocation? Bonita Montero <Bonita.Montero@gmail.com> - 2024-06-24 21:48 +0200
              Re: realloc() - frequency, conditions, or experiences about relocation? Lawrence D'Oliveiro <ldo@nz.invalid> - 2024-06-24 22:59 +0000
            Re: realloc() - frequency, conditions, or experiences about relocation? Bonita Montero <Bonita.Montero@gmail.com> - 2024-06-24 16:19 +0200
            Re: realloc() - frequency, conditions, or experiences about relocation? Lawrence D'Oliveiro <ldo@nz.invalid> - 2024-06-25 07:02 +0000
              Re: realloc() - frequency, conditions, or experiences about relocation? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-06-25 03:05 -0700
                Re: realloc() - frequency, conditions, or experiences about relocation? Richard Damon <richard@damon-family.org> - 2024-06-25 07:21 -0400
                Re: realloc() - frequency, conditions, or experiences about relocation? Phil Carmody <pc+usenet@asdf.org> - 2024-06-28 11:01 +0300
                Re: realloc() - frequency, conditions, or experiences about relocation? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-06-28 04:04 -0700
                Re: realloc() - frequency, conditions, or experiences about relocation? James Kuyper <jameskuyper@alumni.caltech.edu> - 2024-06-28 06:37 -0400
                Re: realloc() - frequency, conditions, or experiences about relocation? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-06-28 04:05 -0700
              Re: realloc() - frequency, conditions, or experiences about relocation? James Kuyper <jameskuyper@alumni.caltech.edu> - 2024-06-28 06:36 -0400
          Re: realloc() - frequency, conditions, or experiences about relocation? Bonita Montero <Bonita.Montero@gmail.com> - 2024-06-24 16:16 +0200
            Down the hall, past the water cooler, third door on the left... (Was: realloc() - frequency, conditions, or experiences about) relocation? gazelle@shell.xmission.com (Kenny McCormack) - 2024-06-24 15:44 +0000
              Re: Down the hall, past the water cooler, third door on the left... (Was: realloc() - frequency, conditions, or experiences about) relocation? Bonita Montero <Bonita.Montero@gmail.com> - 2024-06-24 20:16 +0200
  Re: realloc() - frequency, conditions, or experiences about relocation? David Brown <david.brown@hesbynett.no> - 2024-06-17 14:15 +0200
    Re: realloc() - frequency, conditions, or experiences about relocation? Bonita Montero <Bonita.Montero@gmail.com> - 2024-06-17 14:18 +0200
  Re: realloc() - frequency, conditions, or experiences about relocation? Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2024-06-17 15:21 +0200
  Re: realloc() - frequency, conditions, or experiences about relocation? scott@slp53.sl.home (Scott Lurndal) - 2024-06-17 16:50 +0000
    Re: realloc() - frequency, conditions, or experiences about relocation? Michael S <already5chosen@yahoo.com> - 2024-06-17 20:20 +0300
      Re: realloc() - frequency, conditions, or experiences about relocation? scott@slp53.sl.home (Scott Lurndal) - 2024-06-17 19:02 +0000
  Re: realloc() - frequency, conditions, or experiences about relocation? Rosario19 <Ros@invalid.invalid> - 2024-06-18 11:50 +0200
  Re: realloc() - frequency, conditions, or experiences about relocation? Bonita Montero <Bonita.Montero@gmail.com> - 2024-06-25 10:48 +0200
    Re: realloc() - frequency, conditions, or experiences about relocation? Vir Campestris <vir.campestris@invalid.invalid> - 2024-06-25 11:55 +0100
      Re: realloc() - frequency, conditions, or experiences about relocation? Bonita Montero <Bonita.Montero@gmail.com> - 2024-06-25 13:28 +0200
        Re: realloc() - frequency, conditions, or experiences about relocation? Vir Campestris <vir.campestris@invalid.invalid> - 2024-06-26 12:15 +0100
          Re: realloc() - frequency, conditions, or experiences about relocation? Bonita Montero <Bonita.Montero@gmail.com> - 2024-06-26 15:01 +0200
    Re: realloc() - frequency, conditions, or experiences about relocation? DFS <nospam@dfs.com> - 2024-06-25 09:56 -0400
      Re: realloc() - frequency, conditions, or experiences about relocation? Bonita Montero <Bonita.Montero@gmail.com> - 2024-06-25 16:16 +0200

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