Thanks !

but that still make a circular reference because of $self

This works

use strict;
use warnings;

use Devel::Cycle;

package A;

sub new {
    my ( $class, $href ) = @_;
    my $self = { dbi => $$href{dbi} }; 
    $self->{helper} =
        Helper->new( helper_function => sub {
                     &this_is_from_A( $$href{dbi}, @_)
                 }
             );
    bless $self, $class;
}

sub do_something {
    my $self = shift;
    $self->{helper}->called_from_helper();
}

sub this_is_from_A {
    my ($dbi, $arg) = @_;
    print "$arg\nthis_is_from_A using $dbi\n";
}

package Helper;

sub new {
    my $class = shift;
    my %def = ( a => "something");
    my %arg   = ( ref $_[0] eq "HASH" ? ( %def, %{ $_[0] } ) : ( %def,
+ @_ ) );
    my $self  = \%arg;
    bless $self, $class;
}

sub called_from_helper {
    my $self = shift;
    print "called_from_helper\n";
    $self->{helper_function}->("param from Helper");
}

package main;
my $a = A->new( { dbi => "some dbi object" } );
$a->do_something();
$a->do_something();
find_cycle($a);
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