This is what Expect is for. The Expect module handles the pseudo-tty details, so you don't have to!

This program is called 'consumer.pl'. I added a clue for Expect to use to find the end of the output. You can do without the ending markers, you just have to be a little more clever with Expect. This sample program is similar to yours, in that it uses multiple input streams. It writes a file for each stream.

use File::Slurp;

my $out='';
while(<>)
{
  $out .= "1:$_";
}
$out .= "end1\n";
write_file("out1.txt", $out);

$out='';
while(<>)
{
  $out .= "2:$_";
}
$out .= "end2\n";
write_file("out2.txt", $out);
[download]

Here is a program to communicate with it, and send it two streams of data. The Expect module sends control-D with the string "\cD".

use Expect;

my $proc= new Expect();
$proc->spawn("./consumer.pl");

$proc->send("hello there\n");
$proc->send("\cD");
$proc->send("this is\n");
$proc->send("\cD");

$proc->expect(1,
  [
    /end1/ => sub
    {
      exp_continue;
    }
  ],
  [
    /end2/ => sub
    {
      exp_continue;
    }
  ]
);
[download]

I'm sure that this code could be better, it is intended as proof of concept. I have only used Expect a few times. I find it difficult but worthwhile.

minor update: pushed the code around a bit