Difference among sleep() and usleep() in PHP

问题

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"; 
}
?>

回答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.

回答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

回答3:

usleep() is used to delay execution in "microseconds" while sleep() is used to delay execution in seconds. So usleep(25000) is 0.025 seconds.

Is there any difference between the two?

回答4:

Simply

usleep uses CPU Cycles while sleep does not.

sleep takes seconds as argument

while usleep takes microseconds as argument

回答5:

One other difference is sleep returns 0 on success, false on error. usleep doesn't return anything.

来源：https://stackoverflow.com/questions/19557642/difference-among-sleep-and-usleep-in-php