I like this idea. A suggestion for the interface:

use threads::lite;
my $factory = threads::line->new( -threads => 10 ); #reserve 10 thread
+s

my $x_thr = $factory->create( \&doX, \@Xargs, \%optional_configs );
my $y_thr = $factory->create( \&doY, \@Yargs );
[download]

The general ideas are

1. Spawn a number of threads up-front, if you use more, they are spawned as needed. When the factory is created, the threads could run something like:

   sub _default_thread {
      my $thr_id = shift;
      if (defined $s_coderef[$thr_id] && ref $s_coderef[$thr_id] eq 'CODE
   +') {
         $s_coderef[$thr_id]->(@{ $s_param[$thr_id] });
         $s_coderef[$thr_id] = undef;
      }
      else { sleep(1) }
   }
   [download]

2. Pass arguments as single ARRAYref, opening the door for per-thread configuration.

This is just off the top of my head, so take it as such.