Here's a simple and reliable way of doing it:

#! perl -slw
use strict;
use threads;
use threads::shared;
use Thread::Queue;

our $TIMEOUT //= 10;
our $THREADS //= 16;
our $PROCESSES //= 100;

my $Q = new Thread::Queue;

my $semSTDOUT :shared;

sub tprint{ lock $semSTDOUT; print @_; }

sub worker {
    my $tid = threads->tid;
    while( my $time = $Q->dequeue ) {
        my $pid :shared;
        my $th = async{
           $pid = open my $pipe, '-|', 
               qq[ perl -le"sleep $time; print \$\$, ' done'" ]
               or warn "Failed to start perl with time: $time" and nex
+t;
           local $/;
           return  <$pipe>;
        };
        sleep 1;
        tprint "$tid: Started pid $pid for $time seconds";
        my $t = 0;
        sleep 1 while kill( 0, $pid ) and ++$t < $TIMEOUT;
        if( kill( 0, $pid ) ) {
            tprint "$tid: $pid still running; killing";
            kill 9, $pid;
        }
        else {
            tprint "$tid: $pid completed sucessfully";
        }
        my $result = $th->join;
        tprint "$tid: pid $pid returned: '$result'";
        ## Check result;
    }
}

my @workers = map async( \&worker ), 1 .. $THREADS;

$Q->enqueue( map int( rand 2 * $TIMEOUT ), 1 .. $PROCESSES );
$Q->enqueue( (undef) x $THREADS );

$_->join for @workers;

__END__
[23:21:02.98] c:\test>857569 -THREADS=4 -PROCESSES=10 -TIMEOUT=10
1: Started pid 4032 for 2 seconds
4: Started pid 3848 for 15 seconds
2: Started pid 3436 for 17 seconds
3: Started pid 2392 for 14 seconds
1: 4032 completed sucessfully
1: pid 4032 returned: '4032 done
'
1: Started pid 3640 for 11 seconds
4: 3848 still running; killing
4: pid 3848 returned: ''
2: 3436 still running; killing
2: pid 3436 returned: ''
3: 2392 still running; killing
3: pid 2392 returned: ''
4: Started pid 2872 for 7 seconds
3: Started pid 3604 for 3 seconds
1: 3640 still running; killing
1: pid 3640 returned: ''
3: 3604 completed sucessfully
3: pid 3604 returned: '3604 done
'
1: Started pid 1156 for 6 seconds
3: Started pid 4452 for 3 seconds
4: 2872 completed sucessfully
4: pid 2872 returned: '2872 done
'
3: 4452 completed sucessfully
3: pid 4452 returned: '4452 done
'
1: 1156 completed sucessfully
1: pid 1156 returned: '1156 done
'
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