my $c;
while( sleep 1 ) {
    print "timer event";
    $c = scalar keys %results;
    last if $c;
}

pp $c;

##</code><code>##

$ perl5.14.1 x.pl
timer event
15466

$ perl5.14.1 x.pl
timer event
timer event
436817

$ perl5.14.1 x.pl
timer event
timer event
445051

$ perl5.14.1 x.pl
timer event
timer event
499204

##</code><code>##

#! perl -lw
use strict;
use bignum;
use threads;
use threads::shared;
use Data::Dump qw[ pp ];

my %results :shared;
async {
    my %comps;
    for my $i ( 1 .. 1e6 ) {
        $comps{ $i } = $i ** $i;
    }
    lock(%results);
    %results = %comps;
}->detach;

my $c;
while( sleep 1 ) {
    print "timer event";
    $c = do {
        lock(%results);
        scalar keys %results;
    };
    last if $c;
}

pp $c;

##</code><code>##

my %results :shared;
my $done    :shared;
async {
    my %comps;
    for my $i ( 1 .. 1e6 ) {
        $comps{ $i } = $i ** $i;
    }
    %results = %comps;
    $done++;  # using $done = 1 doesn't want to work - more thought required!
}->detach;

my $c;
while( sleep 1 ) {
    print "timer event";
    last if $done;
}

pp scalar keys %results;