Caching on shared server - security issue for local cache directory?

I am working with this script: http://www.cforcoding.com/2009/05/supercharging-javascript-part-4-caching.html

Basically the instructions recommend not to use caching if it will be used on a shared server.

Now I am using another script which dynamically generates a gif image from a font file and the text I provide and stores it in a local cache drive. Here is part of that code:

$hash = md5(basename($font_file) . $font_size . $font_color .
        $background_color . $transparent_background . $text) ;
$cache_filename = $cache_folder . '/' . $hash . $extension ;
if($cache_images && ($file = @fopen($cache_filename,'rb'))) {
header('Content-type: ' . $mime_type) ;
while(!feof($file))
    print(($buffer = fread($file,$send_buffer_size))) ;
fclose($file) ;
exit ;
}

So my 2 questions are:

1) For the code I pasted he开发者_运维百科re, is there any security issue?

2) And can I just use this piece of code which is used for caching with the website url I provided at the beginning ( http://www.cforcoding.com/2009/05/supercharging-javascript-part-4-caching.html ) Basically replace their caching method with this one to avoid security issues as mentioned. Or do you recommend some other method?

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The author of the cforcoding.com guide was worried about security on a shared host because he was assuming CACHE_DIR was going to be a shared directory such as /tmp. But there is no reason you have to use /tmp for an arbitrary cache directory. You can just use a subdirectory from your user folder. So in your case as long as $cache_folder is not /tmp or another shared directory you will be okay (such as /home/user/mycache).