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Re: Failing Malloc

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On 09/12/2012 05:27 PM, Ian Collins wrote:
> On 09/13/12 09:20 AM, James Kuyper wrote:
>> On 09/12/2012 04:07 PM, Eric wrote:
>>> Hi What is a good way to respond to a failed Malloc (returns Null)? I do
>>> not want to call Abort or Exit immediately.
>>
>> That depends entirely upon what your program is doing. There's only one
>> general piece of advice that's applicable: do NOT do anything with that
>> null pointer value other than copying it or comparing it to other pointers.
>>
>> My own code would generate an error message identifying the fact that
>> malloc() failed, along with the name of the function that called it, and
>> the name of the file containing that function. That much is required by
>> the coding standards for the project I'm working on. Everything else I
>> will say about this reflects my own personal requirements. If the
>> failure occurred inside a loop, the error message would indicate the
>> value of the loop index at the time the problem was identified. If the
>> message would otherwise be identical to another message that could be
>> produced in the same block of code, something will be added to it to
>> allow unique identification of the particular call to malloc() that
>> triggered the problem. That function would then clean up anything that
>> it needed to clean up, and then return an error code to the calling
>> function.
> 
> I can understand this approach on a single use embedded system where 
> such a failure may be repeatable. Do error messages provide any useful 
> data on a multi-user system given the generally random memory usage 
> patterns?

While the systems my programs normally run on are nominally multi-user,
there's one user-id that is used to start the production manager
program. All other programs in the production system (including mine)
are started by the manager, directly or indirectly, and therefore all
run using the same user id. For practical purposes, it's a single-user
system (and definitely NOT an embedded one).

As I said, for failed malloc() calls the information provided by those
error messages is seldom of much use - it's just part of a general
framework for error handling that I've found useful. However, most of
the problems that come up are data-driven, and are unaffected by the
"random memory use patterns" of other programs that might be running at
the same time on the same system. For those kinds of problems, I've
found it a very useful framework.

This is example of how the right way to deal with errors depends very
much on the context in which those errors have to be dealt with, which
is precisely the point I was making.

I was recently assigned to help another group with their work - when it
fails, their software provides much less information in the error
messages than mine does. I keenly miss that information.

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Failing Malloc Eric <nospam@nospam.com> - 2012-09-12 20:07 +0000
  Re: Failing Malloc Xavier Roche <xroche@free.fr.NOSPAM.invalid> - 2012-09-12 22:12 +0200
    Re: Failing Malloc William Ahern <william@wilbur.25thandClement.com> - 2012-09-12 14:25 -0700
  Re: Failing Malloc Andrew Cooper <andrew@nospam.example.com> - 2012-09-12 21:21 +0100
    Re: Failing Malloc Eric <nospam@nospam.com> - 2012-09-12 20:34 +0000
      Re: Failing Malloc Paul N <gw7rib@aol.com> - 2012-09-12 13:46 -0700
        Re: Failing Malloc Eric <nospam@nospam.com> - 2012-09-13 20:21 +0000
          Re: Failing Malloc Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-09-13 17:31 -0400
          Re: Failing Malloc James Kuyper <jameskuyper@verizon.net> - 2012-09-13 17:57 -0400
      Re: Failing Malloc John Gordon <gordon@panix.com> - 2012-09-12 20:55 +0000
        Re: Failing Malloc William Ahern <william@wilbur.25thandClement.com> - 2012-09-12 14:33 -0700
        Re: Failing Malloc falk@rahul.net (Edward A. Falk) - 2012-09-13 22:43 +0000
      Re: Failing Malloc James Kuyper <jameskuyper@verizon.net> - 2012-09-12 17:37 -0400
      Re: Failing Malloc Johann Klammer <klammerj@NOSPAM.a1.net> - 2012-09-13 08:57 +0200
  Re: Failing Malloc James Kuyper <jameskuyper@verizon.net> - 2012-09-12 17:20 -0400
    Re: Failing Malloc Ian Collins <ian-news@hotmail.com> - 2012-09-13 09:27 +1200
      Re: Failing Malloc James Kuyper <jameskuyper@verizon.net> - 2012-09-12 17:56 -0400
        Re: Failing Malloc Ian Collins <ian-news@hotmail.com> - 2012-09-13 10:28 +1200
          Re: Failing Malloc James Kuyper <jameskuyper@verizon.net> - 2012-09-12 18:57 -0400
            Re: Failing Malloc William Ahern <william@wilbur.25thandClement.com> - 2012-09-12 16:21 -0700
            Re: Failing Malloc Ian Collins <ian-news@hotmail.com> - 2012-09-13 12:07 +1200
              Re: Failing Malloc James Kuyper <jameskuyper@verizon.net> - 2012-09-13 13:18 -0400
                Re: Failing Malloc Ian Collins <ian-news@hotmail.com> - 2012-09-14 07:37 +1200
                Re: Failing Malloc James Kuyper <jameskuyper@verizon.net> - 2012-09-13 16:05 -0400
                Re: Failing Malloc William Ahern <william@wilbur.25thandClement.com> - 2012-09-13 14:21 -0700
                Re: Failing Malloc James Kuyper <jameskuyper@verizon.net> - 2012-09-13 17:38 -0400
                Re: Failing Malloc William Ahern <william@wilbur.25thandClement.com> - 2012-09-13 14:03 -0700
                Re: Failing Malloc Ian Collins <ian-news@hotmail.com> - 2012-09-15 10:01 +1200
            Re: Failing Malloc Philip Lantz <prl@canterey.us> - 2012-09-14 02:50 -0700
  Re: Failing Malloc Kaz Kylheku <kaz@kylheku.com> - 2012-09-12 21:36 +0000
  Re: Failing Malloc Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-09-12 17:41 -0400
  Re: Failing Malloc Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2012-09-12 16:07 -0600
    Re: Failing Malloc "christian.bau" <christian.bau@cbau.wanadoo.co.uk> - 2012-09-12 16:03 -0700
  Re: Failing Malloc Kenneth Brody <kenbrody@spamcop.net> - 2012-09-12 19:24 -0400
  Re: Failing Malloc The Great Firewall of China Blue <chine.bleu@yahoo.com> - 2012-09-12 16:34 -0700
  Re: Failing Malloc Malcolm McLean <malcolm.mclean5@btinternet.com> - 2012-09-13 00:14 -0700

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