sleep¶
sleep() is a PHP function which stops the execution for a given number of seconds.
In web security, stopping a process makes it vulnerable to DOS attack : the process waits, doing nothing yet using resources, allowing an attacker to saturate the server.
On the other hand, slowing down a process reduces the efficiency of a brute force attack. A milli second of sleep may not be significant for a legit user, but it may slow down dramatically any brute force attack, that requires millions of tests.
This also covers usleep, which stops the execution of PHP for a given number of milliseconds; time_sleep_until(), which sleeps until a specified date; time_nanosleep(), which stops the execution of PHP for a given number of nanoseconds.
<?php
// sleeps for 3 seconds
sleep(3);
// sleeps for 2 seconds
usleep(2000000);
?>
See also Mastering PHP’s sleep() and usleep() Functions for Time Delays
