Quickly and lightly pick a random file from a folder

Question

Im working on a site with multiple div containers. All of them have one common class, called qcnt , defining their structure, general looks and position.

They each have also assigned a different class, one of about 100, to give each of them one image of about 100 respective sets of about 4 images as the background-image . These sets are currently organized in folders for each class. The CSS for each class currently references a file called random.php , which i found on the web that automatically returns one of the images in their respective folder randomly.

I figured that this is a very performance-intensive task to let the server run for 25 to 100 or more containers per page visit.

I'd like to know what approach would be more reasonable and effective in this scenario. Thanks in advance!

I could post the random.php code here, but i'll guess that my general structure is an ineffective approach from the ground up.

EDIT: Okay, i did not realize this, here is the code:

<?php
$folder = '.';

$extList = array();
$extList['gif'] = 'image/gif';
$extList['jpg'] = 'image/jpeg';
$extList['jpeg'] = 'image/jpeg';
$extList['png'] = 'image/png';


$img = null;

if (substr($folder,-1) != '/') {
    $folder = $folder.'/';
}

if (isset($_GET['img'])) {
$imageInfo = pathinfo($_GET['img']);
if (
    isset( $extList[ strtolower( $imageInfo['extension'] ) ] ) &&
    file_exists( $folder.$imageInfo['basename'] )
) {
    $img = $folder.$imageInfo['basename'];
}
} else {
$fileList = array();
$handle = opendir($folder);
while ( false !== ( $file = readdir($handle) ) ) {
    $file_info = pathinfo($file);
    if (
        isset( $extList[ strtolower( $file_info['extension'] ) ] )
    ) {
        $fileList[] = $file;
    }
}
closedir($handle);

if (count($fileList) > 0) {
    $imageNumber = time() % count($fileList);
    $img = $folder.$fileList[$imageNumber];
}
}

if ($img!=null) {
$imageInfo = pathinfo($img);
$contentType = 'Content-type: '.$extList[ $imageInfo['extension'] ];
header ($contentType);
readfile($img);
} else {
if ( function_exists('imagecreate') ) {
    header ("Content-type: image/png");
    $im = @imagecreate (100, 100)
        or die ("Cannot initialize new GD image stream");
    $background_color = imagecolorallocate ($im, 255, 255, 255);
    $text_color = imagecolorallocate ($im, 0,0,0);
    imagestring ($im, 2, 5, 5,  "IMAGE ERROR", $text_color);
    imagepng ($im);
    imagedestroy($im);
}
}

?>

Answer 1

First, add an http cache expiration to your random.php: How to use HTTP cache headers with PHP

You don't need a lot, anything from 1 minute to half an hour should be a good balance depending on your exact needs (lower cache = less performance but quicker to update if you make changes).

Second, add a random variable from 1-100 to your CSS like so:

random.php?b=13
random.php?b=79
random.php?b=27
random.php?b=1
...

The random variable will ensure that even though you're caching random.php, each container will still get a random image. But because you've added caching and are restricting the variable to 1-100, the max number of calls you'll see on average is 100 / cache time regardless of your site load.