回答

<?php
$descriptorspec = array(
   0 => array("pipe", "r"),
   1 => array("pipe", "w"),
   2 => array("pipe", "r")
);
$process = proc_open('php test_gen.php', $descriptorspec, $pipes, null, null); //run test_gen.php
echo ("Start process:\n");
if (is_resource($process))
{
    fwrite($pipes[0], "start\n");    // send start
    echo ("\n\nStart ....".fgets($pipes[1],4096)); //get answer
    fwrite($pipes[0], "get\n");    // send get
    echo ("Get: ".fgets($pipes[1],4096));    //get answer
    fwrite($pipes[0], "stop\n");    //send stop
    echo ("\n\nStop ....".fgets($pipes[1],4096));  //get answer

    fclose($pipes[0]);
    fclose($pipes[1]);
    fclose($pipes[2]);
    $return_value = proc_close($process);  //stop test_gen.php
    echo ("Returned:".$return_value."\n");
}
?>

<?php
$keys=0;
function play_stop()
{
global $keys;
        $stdin_stat_arr=fstat(STDIN);
        if($stdin_stat_arr[size]!=0)
        {
            $val_in=fread(STDIN,4096);
            switch($val_in)
            {
            case "start\n":    echo "Started\n";
                    return false;
                    break;
            case "stop\n":    echo "Stopped\n";
                    $keys=0;
                    return false;
                    break;
            case "pause\n":    echo "Paused\n";
                    return false;
                    break;
            case "get\n":    echo ($keys."\n");
                    return true;
                    break;
            default:    echo("Передан не верный параметр: ".$val_in."\n");
                    return true;
                    exit();
            }
        }else{return true;}
}
while(true)
{
while(play_stop()){usleep(1000);}
while(play_stop()){$keys++;usleep(10);}
}
?>