PHP长轮询失败

Question

I have this loop to long poll:

$time = time(); //send a blank response after 15sec
    while((time() - $time) < 15) {
            $last_modif = filemtime("./logs.txt");
            if($_SESSION['lasttime'] != $last_modif) {
                $_SESSION['lasttime'] = $last_modif;
                $logs = file_get_contents("./logs.txt");
                print nl2br($logs);
                ob_flush();
                flush();
                die();
        }

        usleep(10000);
    }

problem is: the "if" condition is never entered in the middle of the while loop, even if logs.txt is modified. I have to wait 15sec till the next call to this file to obtain the updated content (so it becomes a regular, "setTimeout style" AJAX polling, not a long-poll). Any idea why ?

Answer 1

This is because of the filemtime() function : its results are cached. Thus each time your loop is executed the timestamp's the same for 15 seconds.

I have not tried it myself, but according to w3cschools :

The result of this function are cached. Use clearstatcache() to clear the cache.

Hope that helps !