многопоточность в пхп

<? // index.php
system('php -f thread1.php &');
system('php -f thread2.php &');
?>

<? // index.php 
system('php -f thread1.php &'); 
system('php -f thread2.php &'); 
?>

//Author: Esrun - http://www.onlinehoster.com

$urls = array("http://www.google.com",
"http://www.yahoo.com", 
"http://www.msn.com", 
"http://www.ask.com",
"http://www.esrun.co.uk", 
"http://www.onlinehoster.com");

$socketh = curl_multi_init();

foreach($urls as $i => $url){
  $socket[$i] = curl_init($url);
  curl_setopt(
     $socket[$i], CURLOPT_RETURNTRANSFER, 1);
  curl_setopt(
     $socket[$i], CURLOPT_FOLLOWLOCATION, 1);
  curl_multi_add_handle($socketh, $socket[$i]);
}

do { 
   $x = curl_multi_exec($socketh, $working); 
} while ($working);

foreach($urls as $i => $url) {
  $data[] = curl_multi_getcontent($socket[$i]);
  curl_close($socket[$i]);
}

print_r($data);