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From:	Krzysztof Duleba <krzysan AT skrzynka DOT pl>
Subject:	Re: perl - segfault on "free unused scalar"
Date:	Wed, 27 Jul 2005 18:56:19 +0200
Lines:	44
Message-ID:	<dc8ebq$36m$1@sea.gmane.org>
References:	<dc7n8k$m72$1 AT sea DOT gmane DOT org> <42E76865 DOT 4000301 AT familiehaase DOT de> <dc82t0$r0a$1 AT sea DOT gmane DOT org> <42E7B413 DOT 8040203 AT familiehaase DOT de>
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Gerrit P. Haase wrote:

>>> $ ./inter.pl
>>> perl> sub foo($){$a=shift;foo($a+1);}
>>> perl> foo 1
>>> Out of memory during request for 4040 bytes, total sbrk() is 
>>> 402624512 bytes!
>>> Segmentation fault (core dumped)
>>
>> Another version (with "my $a"):
>>
>> perl> sub foo($){my $a=shift;foo($a+1);}
>> perl> foo 1
>> Out of memory during "large" request for 134221824 bytes, total sbrk() 
>> is 304633856 bytes at (eval 19) line 1.
>> perl> foo 1
>> Bad realloc() ignored at (eval 19) line 1.
>> Segmentation fault (core dumped)
>>
>> Is this a perl bug, Cygwin bug, or just a feature?
> 
> I don't know.  Maybe it is a Windows feature that applications running
> out of memory are crashing?

But there's plenty of memory left when perl crashes. I have 1 GB RAM and 1 
GB swap file.

I've simplified the test case. It seems that Cygwin perl can't handle too 
much memory. For instance:

$ perl -e '$a="a"x(200 * 1024 * 1024); sleep 9'

OK, this could have failed because $a might require 200 MB of continuous 
space. But hashes don't, do they? Then why does the following code fail?

$ perl -e '$a="a"x(1024 * 1024);my %b; $b{$_}=$a for(1..400);sleep 9'

Or that one?

$ perl -e '$a="a"x(50 * 1024 * 1024);$b=$a;$c=$a;$d=$a;$e=$a;sleep 10'

On linux there's no such problem - perl can use all available memory.

Krzysztof Duleba


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