#!/usr/bin/perl -w
use strict;
use Scalar::Util qw(weaken);

my $data = [1, 2, 3];

print time, " test 0: main start\n";
&gogogo();
print time, " test 3: main end\n";

sub gogogo {
    print time, " test 1: func start\n";
    my @h;
    for (1 .. 200000) {
        my %hash = (data => $data);
        weaken($hash{data});
        push @h, \%hash;
    }
    print time, " test 2: func end\n";
    undef $data;
    return;
}
[download]

The undef can't be the last statement for reasons unclear to me.