Hi All,

I'm now working on a daemon and am trying to improve garbage collection. Until now, I was under the impression that collection was completely automatic, but this quick test says otherwise (on Linux):

#!/usr/bin/perl
use strict;
use warnings;

show_size();
{
    my @var=(0..1000000);
    show_size();
}
show_size();
exit(0);

sub show_size {
    local $/;
    open(my $pfh, '<', "/proc/$$/status") || die $!;
    my $size = <$pfh> =~ /VmSize:\s+(\d+)/
               ? $1
               : 'unknown';
    close($pfh);
    print "Process size: $size\n";
}

# Output is
# Process size: 49956
# Process size: 53864
# Process size: 53864

[download]

But, if I add in some explicit undefs, the result changes:

#!/usr/bin/perl
use strict;
use warnings;

show_size();
{
    my @var=(0..1000000);
    show_size();
    undef @var;
}
show_size();
exit(0);

sub show_size {
    local $/;
    open(my $pfh, '<', "/proc/$$/status") || die $!;
    my $size = <$pfh> =~ /VmSize:\s+(\d+)/
               ? $1
               : 'unknown';
    close($pfh);
    print "Process size: $size\n";
    undef $pfh;
    undef $size;
}

# Output is
# Process size: 49660
# Process size: 53568
# Process size: 49660

[download]

I was under the impression that when a variable went out of scope it would get cleaned up by Perl's automatic garbage collection. But if that's the case, why does the process size not go down after @var falls out of scope without the explicit undef? Am I misunderstanding how garbage collection works? A colleague says that Perl will free up the memory for re-use, but won't let it go. Is this how it really works?

Either way, what is the best practice for controlling memory use in a daemon setup? Any insights appreciated.

cLive ;-)

In reply to Understanding garbage collection specifics... by cLive ;-)

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