Hi Monks, I'm trying to understand the garbage collector. Please have a look at my code example:

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

package Foo;

sub new {
    my $self = bless { }, shift;
    for (1..2_000_000) {
        $self->{x} .= "x" x 1000;
    }
    return $self;
}

package Bar;

sub new {
    my $self = bless { }, shift;
    for (1..2_000_000) {
        $self->{$_} = "x" x 1000;
    }
    return $self;
}

package main;

print "### Test Foo\n";
my $foo = Foo->new;

print "Object created\n";
print "Size: ", qx{ps -p $$ -o rss=};

$foo = undef;
sleep 3;

print "Object destroyed\n";
print "Size: ", qx{ps -p $$ -o rss=};

print "### Test Bar\n";
my $bar = Bar->new;

print "Object created\n";
print "Size: ", qx{ps -p $$ -o rss=};

$bar = undef;
sleep 3;

print "Object destroyed\n";
print "Size: ", qx{ps -p $$ -o rss=};
[download]

### Test Foo
Object created
Size: 1955472
Object destroyed
Size:  2348
### Test Bar
Object created
Size: 2647552
Object destroyed
Size: 2631164

The Foo example is that what I expect. But I don't understand why the memory is not releases back to the operating system in the Bar example.

Could someone bring some light into my darkness?