Neither it seems is ikegami's original suggestion:

#! perl -slw
use strict;
use Data::Dump qw[ pp ];
use Time::HiRes qw[ time ];
use List::Util qw[ shuffle ];
use threads;
use threads::shared;

our $START //= 'aaa';
our $END   //= 'zzz';

my %sems :shared = map{ my $n :shared = 0; $_ => \$n } $START .. $END;
my %hash :shared = map{ $_ => 0 } $START .. $END;

my $start = time;
$_->join for map{
    async{
        my @order = shuffle keys %hash;
        for ( @order ) {
            lock ${ $sems{ $_ } };
            ++$hash{ $_ };
        }
    }
} 1 .. 4;

printf "Lock scalar ref took %.3f seconds\n", time() - $start;

my @fails = grep $_ != 4, values %hash;

warn @fails . " fails\n" if @fails;

__END__
C:\test>909437-3
Lock scalar ref took 2.937 seconds
2840 fails
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