See the Parallel::ForkManager demonstration, here. Something similar can be done with MCE::Child. Subsequently, MCE. Notice the PIDs in the 2nd demonstration where the workers persist.

MCE::Child

use strict;
use warnings;
use MCE::Child qw( );
use Time::HiRes qw( time );
 
my @testLists = qw( sun moon wind air );
my $opts = 'foo';
my $status = 0;

sub regressions {
   my ($opts, $list) = @_;
   print "$$: $list\n";
   sleep 1; # simulate processing
   return 1;
}

my $start = time();

MCE::Child->init(
   max_workers => 2,
   on_finish => sub {
      my ( $pid, $exit_code, $ident, $exit_signal, $core_dump, $data )
+ = @_;
      if ( $exit_code || $exit_signal || $core_dump ) {
         # Handle error.
      }
      $status += $data->{ status };
   }
);
 
for my $list ( @testLists ) {
   MCE::Child->create(sub {
      my $status = regressions( $opts, $list );
      return { status => 1 };
   });
}

MCE::Child->wait_all();
print "status: $status\n";
printf "duration: %0.3f seconds\n", time() - $start;

__END__
27481: sun
27482: moon
27483: wind
27484: air
status: 4
duration: 2.013 seconds
[download]

MCE

use strict;
use warnings;
use MCE::Loop qw( );
use Time::HiRes qw( time );
 
my @testLists = qw( sun moon wind air );
my $opts = 'foo';
my $status = 0;

sub regressions {
   my ($opts, $list) = @_;
   print "$$: $list\n";
   sleep 1; # simulate processing
   return 1;
}

my $start = time();

MCE->new(
   max_workers => 2,
   chunk_size  => 1,
   input_data  => \@testLists,
   gather      => sub { $status += $_[0] },
   user_func   => sub {
      my $list   = $_;
      my $status = regressions( $opts, $list );
      MCE->gather( $status );
   },
)->run();
 
print "status: $status\n";
printf "duration: %0.3f seconds\n", time() - $start;

__END__
27562: sun
27563: moon
27562: wind
27563: air
status: 4
duration: 2.005 seconds
[download]