操作文件加锁

$file = 'log.txt';  
$fp = fopen($file, 'a+');  
if(!is_writable($file)){  
    exit("The $file is not writable!");  
}  
flock($fp, LOCK_EX);// 加锁  
fwrite($fp, 'here');  
flock($fp, LOCK_UN);// 解锁  
fclose($fp);