Difference among sleep() and usleep() in PHP

Question

Can any body explain me what is the difference among sleep() and usleep() in PHP.

I have directed to use following scripts to do chat application for long pulling but in this script I am getting same effect using usleep(25000); or without usleep(25000);

page1.php

<script src="http://ajax.googleapis.com/ajax/libs/jquery/1/jquery.min.js"         type="text/javascript"></script>  <script> var lpOnComplete = function(response) {     console.log(response);     // do more processing     lpStart(); };  var lpStart = function() {     $.post('page2.php', {}, lpOnComplete, 'json'); };  $(document).ready(lpStart); </script> 

page2.php

<?php $time = time(); while((time() - $time) < 30) {     // query memcache, database, etc. for new data     $data = getLatest();      // if we have new data return it     if(!empty($data)) {         echo json_encode($data);         break;     }      usleep(25000); }  function getLatest() {     sleep(2);     return "Test Data";  } ?> 

Answer 1

The argument to sleep is seconds, the argument to usleep is microseconds. Other than that, I think they're identical.

sleep($n) == usleep($n * 1000000) 

usleep(25000) only sleeps for 0.025 seconds.

Answer 2

sleep() allows your code to sleep in seconds.

• sleep(5); // sleeps for 5 seconds

usleep() allows your code with respect to microseconds.

• usleep(2500000); // sleeps for 2.5 seconds