use IO::Select;

open FHANDA,"processA|" || die("..");
open FHANDB,"processA|" || die("..");
open FHANDC,"processA|" || die("..");

$Select = IO::Select->new();
$Select->add(*FHANDA);
$Select->add(*FHANDB);
$Select->add(*FHANDC);
if (@ready = $slect->can_read(0))
{
  for (@ready)
  {
    #Process the file handle (do the read and write)
  }
}