Re: Memory leak with Inline::C

From: Tassilo v. Parseval (tassilo.von.parseval_at_rwth-aachen.de)
Date: 07/11/04 

Date: Sun, 11 Jul 2004 22:22:59 +0200

Also sprach Anno Siegel:

> I'm seeing a memory leak with the Inline code below. The sub by_inline()
> returns a varying number of scalars, which is probably the crux of the
> matter.

Actually, the problem is that your program may produce infinite loops.

> The code works as expected (returning the exponents of 2 used in the
> binary representation of the argument), but the loop leaks. It leaks
> just the same when by_inline() is called in void context.
>
> I don't see anything obviously wrong with the code, in particular the
> newly created SVs are carefully mortalized, but I'd like a second opinion.
>
> I'd also be grateful if one or the other could find the time to run
> the code and report back. For me, the process grows to 500+ MB before
> the loop runs out (I kill it when swapping becomes audible).
>
> Conditions here:
> Darwin 7.4.0, Perl 5.8.4, Inline 0.44, gcc 3.3
>
> Update:
> It also leaks on a Linux with Perl 5.8.1, same Inline, unknown gcc.
>
> Anno
>
> #!/usr/local/bin/perl
> use strict; use warnings; $| = 1;
> use Vi::QuickFix;
>
> my @res = by_inline( int rand 2 ** 32) for 1 .. 100_000;

A value in the above range might not fit into a signed 32bit integer. In
this case it gets wrapped around and 'x' in the below C function ends up
being negative. So 'x' will eventually become -1 and never turn zero.
And there you have your infinite while-loop.

> use Inline C => <<EOC;
> void by_inline( int x) {
> int i;
> Inline_Stack_Vars;
> Inline_Stack_Reset;
> i = 0;
> while ( x ) {
> if ( x & 1 ) {
> Inline_Stack_Push( sv_2mortal( newSViv( i)));
> }
> x >>= 1;
> i ++;
> }
> Inline_Stack_Done;
> }
> EOC
> __END__

One fix would be to increase the range of your numbers:

    void by_inline(double X) {
        long long x = X;
        ...
    }

Tassilo 

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