做了个弱统计，写入到文件中，引起并发问题，加锁解决

function pageCount($fileName){
    if ($fp = fopen($fileName, ‘r+‘)) {
        $startTime = microtime();
        do {
            $canWrite = flock($fp, LOCK_EX | LOCK_NB);
            if (!$canWrite) {
                usleep(round(rand(0, 100) * 1000));
            }
        } while ((!$canWrite) && ((microtime() - $startTime) < 1000));
        if ($canWrite) {
            $count = intval(fgets($fp));
            ++$count;
            ftruncate($fp,0); // 将文件截断到给定的长度 
            rewind($fp); // 倒回文件指针的位置 
            fwrite($fp, $count);
            flock($fp , LOCK_UN);
        }
        fclose($fp);
    }
}