Session 函数
在线手册：中文 英文
PHP手册

session_cache_expire

(PHP 4 >= 4.2.0, PHP 5)

session_cache_expire — Return current cache expire

说明

int session_cache_expire ([ string $new_cache_expire ] )

session_cache_expire() returns the current setting of session.cache_expire.

The cache expire is reset to the default value of 180 stored in session.cache_expire at request startup time. Thus, you need to call session_cache_expire() for every request (and before session_start() is called).

参数

new_cache_expire

If new_cache_expire is given, the current cache expire is replaced with new_cache_expire.

Note: Setting new_cache_expire is of value only, if session.cache_limiter is set to a value different from nocache.

返回值

Returns the current setting of session.cache_expire. The value returned should be read in minutes, defaults to 180.

范例

Example #1 session_cache_expire() example

<?php

/* set the cache limiter to 'private' */

session_cache_limiter('private');
$cache_limiter = session_cache_limiter();

/* set the cache expire to 30 minutes */
session_cache_expire(30);
$cache_expire = session_cache_expire();

/* start the session */

session_start();

echo "The cache limiter is now set to $cache_limiter<br />";
echo "The cached session pages expire after $cache_expire minutes";
?>

参见

Session 函数
在线手册：中文 英文
PHP手册
PHP手册 - N: Return current cache expire

用户评论:

karel at narfum dot org (27-Apr-2011 10:33)

What most people also don't know, is that most Linux distributions (Debian and Ubuntu for me atleast) have a cronbjob that cleans up your session dir using the value set in the global /etc/php5/php.ini (which defaults to 24mins). So even if you set a value larger in your scripts, the cronbjob will still cleanup sessions using the global value.

If you run into that situation, you can set the global value higher in /etc/php5/php.ini, disable the cronjob or even better, do your own session cleanup in a non-systemwide directory or a database.

Anonymous (20-Feb-2008 04:50)

The manual probably doesn't stress this enough:

** This has nothing to do with lifetime of a session **

Whatever you set this setting to, it won't change how long sessions live on your server.

This only changes HTTP cache expiration time (Expires: and Cache-Control: max-age headers), which advise browser for how long it can keep pages cached in user's cache without having to reload them from the server.

info at ericbontenbal dot nl (08-Aug-2006 08:34)

you can change the max lifetime for a session with the function ini_set().

<?php
ini_set("session.gc_maxlifetime", "18000");
?>
This will set the max lifetime of the script to 5 hours. You have to use this in every script that you want to change the default lifetime for.

if you want to know the lifetime of your current script, you can use:

<?php
echo ini_get("session.gc_maxlifetime");
?>

lukasz at pilorz dot net (21-Nov-2005 01:49)

I had a problem with session expiration time on a server where I didn't have access to php.ini. My solution was to use session_save_path with my own dir.

djmaze (AT) dragonflycms (23-Sep-2005 03:21)

After recieving a "bogus" mark on a bug report i've tried to find out the differences between cache_expire and what was causing a session delete after 24 minutes.

cache_expire is used for cached session pages and has nothing to do with the session data

The garbage collector controls the session data and destroys sessions which are older then 1440 seconds (24 minutes) by default.

So to keep a session alive longer then 24 minutes (for example when a visitor tries to POST a huge message that took him 1 hour to type), you must modify the session.gc_maxlifetime thru ini_set()

Somehow i couldn't find anything in the PHP documentation regarding this and due to that me (and i think many others) got the wrong ideas regarding PHP sessions.
A few examples to fix session timeout are already posted below but in my opinion they all missed session.gc_maxlifetime

lance_rushing at hotmail dot com (17-Jun-2005 10:47)

I've encountered the same problem of loosing focus when using IE and a javascript window.location.refresh/replace().

After fusing around I found that a <meta http-equiv="refresh" content="600"> works without move the focus on the parent frame's form.  The down side is loading up the browser history and an annoying 'click' in IE on the page load.

bermiferrer[at]akelos[NOSPAM]com (03-Jun-2004 09:11)

Hello,
Some of my customers asked me for a solution form their session not to expire when filling large forms. Sometimes it takes them more than 2 hours to submit (phone, desk customers...).
I know I could have forced an ilayer to be refreshed dynamically and then include PHP code using session_cache_expire() function, but this refreshing a page changes the form focus. So I found this the only solution for them not to loose focus over their form element.

You can make a session not to expire by using this code.
Its a mixture of PHP and JavaScript and can be used on the same page were your code goes or it can be called using an ilayer/iframe from your page.

I know this is not the best practice, but in some cases were user has no control over server globals and security is not important this can help.

Here is the code.

<?

//First of all we prevent browsers from caching the image
header("Cache-Control: no-store, no-cache, must-revalidate");
header("Cache-Control: post-check=0, pre-check=0", false);
header("Pragma: no-cache");
header("Expires: Mon, 26 Jul 1997 05:00:00 GMT");
header("Last-Modified: " . gmdate("D, d M Y H:i:s") . " GMT");

//This piece of code returns a blank gif
if($_GET[img] > 0){
    header('Content-Type: image/gif');
    header("Content-Disposition: inline; filename=".time().".gif");
    echo base64_decode(str_replace("\n","","
R0lGODlhAQABAPcAAAAAAAAAQAAAgAAA/
wAgAAAgQAAggAAg/wBAAABAQABAgABA/
wBgAABgQABggABg/wCAAACAQACAgACA/
wCgAACgQACggACg/wDAAADAQADAgADA/
wD/AAD/QAD/gAD//yAAACAAQCAAgCAA/
yAgACAgQCAggCAg/yBAACBAQCBAgCBA/
yBgACBgQCBggCBg/yCAACCAQCCAgCCA/
yCgACCgQCCggCCg/yDAACDAQCDAgCDA/
yD/ACD/QCD/gCD//0AAAEAAQEAAgEAA/
0AgAEAgQEAggEAg/0BAAEBAQEBAgEBA/
0BgAEBgQEBggEBg/0CAAECAQECAgECA/
0CgAECgQECggECg/0DAAEDAQEDAgEDA/
0D/AED/QED/gED//2AAAGAAQGAAgGAA/
2AgAGAgQGAggGAg/2BAAGBAQGBAgGBA/
2BgAGBgQGBggGBg/2CAAGCAQGCAgGCA/
2CgAGCgQGCggGCg/2DAAGDAQGDAgGDA/
2D/AGD/QGD/gGD//4AAAIAAQIAAgIAA/
4AgAIAgQIAggIAg/4BAAIBAQIBAgIBA/
4BgAIBgQIBggIBg/4CAAICAQICAgICA/
4CgAICgQICggICg/4DAAIDAQIDAgIDA/
4D/AID/QID/gID//6AAAKAAQKAAgKAA/
6AgAKAgQKAggKAg/6BAAKBAQKBAgKBA/
6BgAKBgQKBggKBg/6CAAKCAQKCAgKCA/
6CgAKCgQKCggKCg/6DAAKDAQKDAgKDA/
6D/AKD/QKD/gKD//8AAAMAAQMAAgMAA/
8AgAMAgQMAggMAg/8BAAMBAQMBAgMBA/
8BgAMBgQMBggMBg/8CAAMCAQMCAgMCA/
8CgAMCgQMCggMCg/8DAAMDAQMDAgMDA/
8D/AMD/QMD/gMD///8AAP8AQP8AgP8A/
/8gAP8gQP8ggP8g//9AAP9AQP9AgP9A/
/9gAP9gQP9ggP9g//+AAP+AQP+AgP+A/
/+gAP+gQP+ggP+g///AAP/AQP/AgP/A/
///AP//QP//gP///yH5BAEAAP8ALAAAA
AABAAEAAAgEAP8FBAA7"));
    exit;
}

?>

<!-- HERE YOU CAN INSERT THE HTML OR PHP CODE -->

<img name="keepUpdated" src="<?=$_SELF?>?img=999">
<script language="Javascript">
<!--
var updateEvery = 30;//Seconds
function keepUpdated() {
    timer=setTimeout("updateImage()",1000*updateEvery)
}
function updateImage() {
    var randNum = Math.floor(Math.random()*999);
    document.images.keepUpdated.src ="<?=$_SELF?>?img="+randNum;
    keepUpdated();
}
keepUpdated();
//-->
</script>

I hope this can be helpful for someone.

Bermi Ferrer