coro_timeout.pl

#!/usr/bin/env perl

use strict;
use warnings;
use feature qw/say/;

use Coro;
use Coro::AnyEvent;

my $var;
my $timeout_timer;
my $worker;
my $timeout_watcher;

$timeout_watcher = async {
    $timeout_timer = AE::timer 2, 0, sub {
        if (! eval { $worker->safe_cancel }) {
            eval { $worker->cancel };
            warn "error: $@" if $@;
        }
        say "Worker canceled";
        eval { say $var };
    };
};

$worker = async {
    $var = "Substituted at client!";
    Coro::AnyEvent::sleep 5;
    say "I'm worker"; # <= unreachable!
};

$worker->join;
if (! eval { $timeout_watcher->safe_cancel }) {
    $timeout_watcher->cancel;
}

say "Finished";