PHP stream_set_timeout有什么用

$server="www.yahoo.com";  
$port = 80;  
  
$data="GET / HTTP/1.0rn";  
$data.="Connection: Closern";  
$data.="User-Agent: Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1)rnrn";  
  
$start_time = time();  
$fp=fsockopen($server, $port, $errno, $errstr, 5);  
if (!$fp) {  
die("Connect Timeout.n");  
} else {  
stream_set_blocking($fp, True);  
stream_set_timeout($fp, 3);  
  
fputs($fp, "$data");  
while (!feof($fp)) {  
$text .= fread($fp, 2000);  
  
$diff = time() - $start_time;  
if ($diff > 24) {  
die("Timeout!n");  
}  
  
$status = stream_get_meta_data($fp);  
if ($status[’timed_out’]) {  
die("Stream Timeout!n");  
}  
}  
}  
  
fclose($fp);