$pm->run_on_finish(
     sub {
            my ($pid, $exit_code, $ident) = @_;       
            print "run_on_finish: $ident (pid: $pid) exited " . "with 
+code: [$exit_code]\n";
    insert_into_db(\$dbh, $pid, $exit_code);      
+    
          }
);

for my $host (@hosts) { 
    $pm->start($host) and next; 
    exec(@some_command); 
    print(STDERR "exec failed: $!\n"); _exit($!); 
}

##</code><code>##

my $pm = new Parallel::ForkManager( 20 );

for my $host (@hosts) { 
    $pm->start($host) and next; 
    exec(@some_command); 
    print(STDERR "exec failed: $!\n"); _exit($!); 
}