程序独占该文件，不允许其他操作，直到该程序完成对文件的操作
1 $content = ' 2 asdfasdfasdf 3 asdfasdfasdf 4 asdfasdfasd 5 asdfasdf 6 asdfasdf 7 ';
1 $file = '/var/www/file.txt';
1 $fp = @fopen($file, 'wb') ; 2 if(@feof($file)) return;
3 flock($fp, LOCK_EX);
4 $len = @fwrite($fp, $content);
5 flock($fp, LOCK_UN);
6 @fclose($fp);
7 exec("chmod 777 $file");