use Proc::Queue size => 5, # => 5 parallel processes max.
                qw(system_back);

use POSIX ":sys_wait_h";
use Errno qw(EINTR);

my %pid2date;

sub reap_children {
  my $wait = shift;
  my $pid = waitpid(-1, ($wait ? 0 : WNOHANG));
  if ($pid > 0) {
    print "process for date $pid2date{$pid} (pid $pid) exited with cod
+e ". ($? >> 8) . "\n";
    return 1;
  }
  return ($! == EINTR);
}

while ($currentdate <= $enddate) {
  reap_children(0);
  print "$command\n";
  my $pid = system_back($command);
  $pid2date{$pid} = $currentdate;
  $currentdate = nextdate($currentdate);
}

1 while reap_children(1);
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