This is a somwhat simpler approach and is thread-safe:

#! perl -sw
use strict;
use threads;
use threads::shared;

our $T //= 5;

my $pid :shared;
my( $t ) = threads->create(
    sub{
        my @input;
        $pid = open my $in, '-|', 
            q[ perl -wle"$|++; print() and sleep 1 for 1.. 5" ]
            or die $!;
        push @input, $_ while <$in>;
        return @input;
    }
);

sleep $T;
kill 21, $pid;

my @input = $t->join;

print for @input;

__END__

c:\test>junk82 -T=4
Terminating on signal SIGBREAK(21)
1
2
3
4

c:\test>junk82 -T=5
Terminating on signal SIGBREAK(21)
1
2
3
4
5

c:\test>junk82 -T=6
1
2
3
4
5
[download]

It does have a caveat that you may loose some output buffered by the child process, but is otherwise quite reliable and should work wherever threads do.