Re: C++ Memory Management Question

From	"Paul" <pchrist<nospam>or@yahoo.co.uk>
Newsgroups	comp.lang.c++
Subject	Re: C++ Memory Management Question
Date	2012-01-02 15:54 +0000
Organization	Netfront http://www.netfront.net/
Message-ID	<jdsjvs$2em2$1@adenine.netfront.net> (permalink)
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"Leigh Johnston" <leigh@i42.co.uk> wrote in message 
news:166dnXvy0p2XXZzSnZ2dnUVZ8sadnZ2d@giganews.com...
> On 02/01/2012 11:26, Paul <pchrist wrote:
>> "Leigh Johnston"<leigh@i42.co.uk>  wrote in message
>> news:EaOdnR_ieaQwJZ3SnZ2dnUVZ8nCdnZ2d@giganews.com...
>>> On 01/01/2012 19:36, Paul<pchrist wrote:
>>>> "Leigh Johnston"<leigh@i42.co.uk>   wrote in message
>>>> news:wuqdnZzxuYoWM53SnZ2dnUVZ8iCdnZ2d@giganews.com...
>>>>> On 01/01/2012 14:39, Victor Bazarov wrote:
>>>>>> On 1/1/2012 2:25 AM, Goran wrote:
>>>>>>> On Dec 31 2011, 7:04 pm, Victor Bazarov<v.baza...@comcast.invalid>
>>>>>>> wrote:
>>>>>>>> Neither a word processor nor a video editor should even attempt
>>>>>>>> loading
>>>>>>>> anything if it determines that the attempt might cause it to run 
>>>>>>>> out
>>>>>>>> of
>>>>>>>> memory. If they can't determine that before opening the file, they
>>>>>>>> aren't worth our time to discuss them.
>>>>>>>
>>>>>>> I disagree. There's no guarantee whatsoever that any allocation will
>>>>>>> succeed, so theoretically, your idea is unsound. Practically, it's
>>>>>>> difficult to implement more often than not. I was doing it, and
>>>>>>> looking back, it was an error. E.g. it's easy only if you merely 
>>>>>>> load
>>>>>>> file contents into memory. I don't believe that happens all that
>>>>>>> often.
>>>>>>>
>>>>>>> What you're saying is equivalent to going to supermarket to see
>>>>>>> whether it has mayonnaise, then going back for money, then coming 
>>>>>>> back
>>>>>>> to buy.
>>>>>>
>>>>>> Not at all. There is always some reasonable portion that, when
>>>>>> allocated
>>>>>> fresh, is likely to be granted to the process. And if allocating that
>>>>>> reasonable portion fails, quit and tell the user he can't use that
>>>>>> system for that operation without any changes (e.g. making some more
>>>>>> resources available by either adding spare ones or releasing the ones
>>>>>> currently used). I am saying that if you come to the store to buy
>>>>>> mayonnaise, there is (a) no sense to reach into your pocket if the 
>>>>>> mayo
>>>>>> is not on the shelf (file is missing), (b) no need to buy the
>>>>>> lifetime's
>>>>>> worth in advance (even if you know what your lifetime is going to 
>>>>>> be).
>>>>>> We buy mayo in portions, consume, then come to buy some more. 
>>>>>> Besides,
>>>>>> we have replenishment of money, so it's a bad analogy anyway.
>>>>>>
>>>>>> In 1960s programmers wrote solving large systems of linear equations
>>>>>> (hundreds and even thousands) on a system that only had 100 cells of
>>>>>> memory. How did they manage? What is so different about it when it's
>>>>>> not
>>>>>> 100 but 100 billion cells? There will be problems that aren't going 
>>>>>> to
>>>>>> fit in memory whole. Another example: on MS-DOS there was a text 
>>>>>> editor
>>>>>> called MultiEdit that managed to deal with files much larger than the
>>>>>> available 640KB. How did they do it?
>>>>>>
>>>>>> What I am saying is that there is always a way to deal with large
>>>>>> amounts of data without having to load it all in memory.
>>>>>
>>>>> I agree with Goran; you are talking rubbish; there is no standard way 
>>>>> to
>>>>> determine if an allocation *attempt* will succeed or not; to avoid OOM
>>>>> either pre-allocate whatever you need up front if memory requirements
>>>>> are
>>>>> bounded otherwise you must handle allocation *failures*.
>>>>>
>>>> The problem with this discussion is that its very OS speific.
>>>>
>>>> To create a robust memory managment system would require good knowledge
>>>> of
>>>> the underlying OS and an understanding of all possible allocation
>>>> failures.
>>>>
>>>> I think it is possible that an OS may provide methods for checking
>>>> available
>>>> memory.
>>>>
>>>> I do agree with Carlo that profession programmes should exit gracefully 
>>>> ,
>>>> if
>>>> possible. True it may not always be possible as there may be times when 
>>>> a
>>>> complete system crash is inevitable , but a program should at least 
>>>> *try*
>>>> to
>>>> save work or recover under low memory conditions.
>>>
>>> That is fine if "save work" or "recover" do not allocate memory 
>>> otherwise
>>> they may also suffer a memory allocation failure.  Aborting the program
>>> (what you call "crashing") on allocation failure is perfectly acceptable
>>> for a subset of all possible programs and this is what will happen if 
>>> you
>>> don't handle (catch) allocation failure exceptions such as 
>>> std::bad_alloc.
>>>
>>
>> This is not what I meant by crashing, I said a system crash , that is the 
>> OS
>> encountering a unrecoverable and critical error. You are speaking about
>> aborting a program , a program just dying whenever it encounters an
>> exception..
>
> This thread is not about unrecoverable or critical OS errors; it is about 
> memory allocation failures.
>
> Even if an OS provided a mechanism to determine available memory what 
> guarantee would there be that the amount of available memory reported by 
> such a function would be the same as the amount of available memory when 
> the allocation request is actually made?
>
> Are you suggesting that one should check available memory before calling 
> any function that may allocate memory?  This is of course absurd.
>
No not at all. But such functions may exist.

> Are you suggesting that in C++ one should only use the no-throw version of 
> 'new' and check every allocation request at the site of the request and 
> report an error and "save work" or "recover"?  This is of course absurd.
>
Why is it absurd to check each allocation for a failure?



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Thread

C++ Memory Management Question Datesfat Chicks <datesfat.chicks@gmail.com> - 2011-12-31 08:56 -0500
  Re: C++ Memory Management Question Victor Bazarov <v.bazarov@comcast.invalid> - 2011-12-31 09:44 -0500
    Re: C++ Memory Management Question Datesfat Chicks <datesfat.chicks@gmail.com> - 2011-12-31 10:17 -0500
      Re: C++ Memory Management Question "MikeWhy" <boat042-nospam@yahoo.com> - 2011-12-31 12:56 -0600
      Re: C++ Memory Management Question jt@toerring.de (Jens Thoms Toerring) - 2011-12-31 19:05 +0000
    Re: C++ Memory Management Question Carlo Milanesi <carlo.nospam.milanesi@libero.it> - 2011-12-31 18:18 +0100
      Re: C++ Memory Management Question Victor Bazarov <v.bazarov@comcast.invalid> - 2011-12-31 13:04 -0500
        Re: C++ Memory Management Question Carlo Milanesi <carlo.nospam.milanesi@libero.it> - 2011-12-31 19:42 +0100
        Re: C++ Memory Management Question Goran <goran.pusic@gmail.com> - 2011-12-31 23:25 -0800
          Re: C++ Memory Management Question Victor Bazarov <v.bazarov@comcast.invalid> - 2012-01-01 09:39 -0500
            Re: C++ Memory Management Question Goran <goran.pusic@gmail.com> - 2012-01-01 08:20 -0800
            Re: C++ Memory Management Question Leigh Johnston <leigh@i42.co.uk> - 2012-01-01 19:05 +0000
              Re: C++ Memory Management Question "Paul" <pchrist<nospam>or@yahoo.co.uk> - 2012-01-01 19:36 +0000
                Re: C++ Memory Management Question Leigh Johnston <leigh@i42.co.uk> - 2012-01-01 19:49 +0000
                Re: C++ Memory Management Question "Paul" <pchrist<nospam>or@yahoo.co.uk> - 2012-01-02 11:26 +0000
                Re: C++ Memory Management Question Leigh Johnston <leigh@i42.co.uk> - 2012-01-02 14:32 +0000
                Re: C++ Memory Management Question "Paul" <pchrist<nospam>or@yahoo.co.uk> - 2012-01-02 15:54 +0000
                Re: C++ Memory Management Question Leigh Johnston <leigh@i42.co.uk> - 2012-01-02 16:26 +0000
                Re: C++ Memory Management Question "Paul" <pchrist<nospam>or@yahoo.co.uk> - 2012-01-02 16:58 +0000
                Re: C++ Memory Management Question Leigh Johnston <leigh@i42.co.uk> - 2012-01-02 21:14 +0000
                Re: C++ Memory Management Question Ian Collins <ian-news@hotmail.com> - 2012-01-03 11:11 +1300
                Re: C++ Memory Management Question scott@slp53.sl.home (Scott Lurndal) - 2012-01-03 20:53 +0000
                Re: C++ Memory Management Question Leigh Johnston <leigh@i42.co.uk> - 2012-01-03 21:21 +0000
                Re: C++ Memory Management Question Ian Collins <ian-news@hotmail.com> - 2012-01-04 12:15 +1300
                Re: C++ Memory Management Question gwowen <gwowen@gmail.com> - 2012-01-04 08:20 -0800
                Re: C++ Memory Management Question "Paul" <pchrist<nospam>or@yahoo.co.uk> - 2012-01-02 22:24 +0000
                Re: C++ Memory Management Question Leigh Johnston <leigh@i42.co.uk> - 2012-01-02 22:55 +0000
                Re: C++ Memory Management Question "Paul" <pchrist<nospam>or@yahoo.co.uk> - 2012-01-02 23:27 +0000
                Re: C++ Memory Management Question Nick Keighley <nick_keighley_nospam@hotmail.com> - 2012-01-10 01:01 -0800
                Re: C++ Memory Management Question 88888 Dihedral <dihedral88888@googlemail.com> - 2012-01-02 21:45 -0800
                Re: C++ Memory Management Question Goran <goran.pusic@gmail.com> - 2012-01-03 00:32 -0800
                Re: C++ Memory Management Question "Paul" <pchrist<nospam>or@yahoo.co.uk> - 2012-01-03 17:34 +0000
                Re: C++ Memory Management Question Nick Keighley <nick_keighley_nospam@hotmail.com> - 2012-01-10 00:47 -0800
                Re: C++ Memory Management Question BCFD36 <bcfd36@cruzio.com> - 2012-01-10 22:57 -0800
              Re: C++ Memory Management Question Ian Collins <ian-news@hotmail.com> - 2012-01-03 09:31 +1300
                Re: C++ Memory Management Question Leigh Johnston <leigh@i42.co.uk> - 2012-01-02 21:02 +0000
                Re: C++ Memory Management Question Ian Collins <ian-news@hotmail.com> - 2012-01-03 11:09 +1300
          Re: C++ Memory Management Question Leigh Johnston <leigh@i42.co.uk> - 2012-01-01 18:57 +0000
      Re: C++ Memory Management Question jgk@panix.com (Joe keane) - 2012-01-01 22:04 +0000
        Re: C++ Memory Management Question Carlo Milanesi <carlo.nospam.milanesi@libero.it> - 2012-01-02 00:37 +0100
          Re: C++ Memory Management Question yatremblay@bel1lin202.(none) (Yannick Tremblay) - 2012-01-09 17:41 +0000
            Re: C++ Memory Management Question Carlo Milanesi <carlo.milanesi@libero.it> - 2012-01-13 08:14 -0800
    Re: C++ Memory Management Question Jorgen Grahn <grahn+nntp@snipabacken.se> - 2012-01-01 18:05 +0000
  Re: C++ Memory Management Question Nick Keighley <nick_keighley_nospam@hotmail.com> - 2011-12-31 07:25 -0800
  Re: C++ Memory Management Question Torsten Mueller <dev-null@shared-files.de> - 2011-12-31 16:41 +0100
  Re: C++ Memory Management Question Nobody <nobody@nowhere.com> - 2012-01-01 09:16 +0000
    Re: C++ Memory Management Question Datesfat Chicks <datesfat.chicks@gmail.com> - 2012-01-02 16:48 -0500
      Re: C++ Memory Management Question Goran <goran.pusic@gmail.com> - 2012-01-03 00:02 -0800
        Re: C++ Memory Management Question Datesfat Chicks <datesfat.chicks@gmail.com> - 2012-01-03 12:53 -0500
          Re: C++ Memory Management Question Nobody <nobody@nowhere.com> - 2012-01-03 19:46 +0000
          Re: C++ Memory Management Question Goran <goran.pusic@gmail.com> - 2012-01-04 00:11 -0800
            Re: C++ Memory Management Question Nobody <nobody@nowhere.com> - 2012-01-04 09:30 +0000
    Re: C++ Memory Management Question Jorgen Grahn <grahn+nntp@snipabacken.se> - 2012-01-04 19:28 +0000
      Re: C++ Memory Management Question Nobody <nobody@nowhere.com> - 2012-01-04 22:09 +0000
        Re: C++ Memory Management Question Jorgen Grahn <grahn+nntp@snipabacken.se> - 2012-01-05 11:43 +0000
  Re: C++ Memory Management Question Christian Gollwitzer <auriocus@gmx.de> - 2012-01-01 18:13 +0100
    Re: C++ Memory Management Question "io_x" <a@b.c.invalid> - 2012-01-01 20:11 +0100
    Re: C++ Memory Management Question Datesfat Chicks <datesfat.chicks@gmail.com> - 2012-01-02 16:51 -0500
  Re: C++ Memory Management Question Simon Quinn <sq@nospam.com> - 2012-01-05 07:54 +0000
  Re: C++ Memory Management Question darylew@gmail.com - 2012-01-10 10:19 -0800

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