Hacky caching with PHP

query.php

$key = $_SERVER['REMOTE_ADDR'] . serialize($_REQUEST);
if(strlen($key) < 500){ // help prevent flooding.
        $key = md5($key);
        // global so we can find it in the shutdown function
        $GLOBALS['wordpress_temp_file'] = dirname(__FILE__).'/cache/wp_'.basename($key);
        if(is_file($GLOBALS['wordpress_temp_file']) && filemtime($GLOBALS['wordpress_temp_file']) > (time() - 3600)){
                $data = unserialize(file_get_contents($GLOBALS['wordpress_temp_file']));
                echo $data['content'];
                exit;
        }
        ob_start();
        function wordpress_shutdown() {
                $data = array(
                        'request' => $_REQUEST,
                        'content' => ob_get_clean(),
                );
                if(isset($GLOBALS['wordpress_temp_file'])) {
                        file_put_contents( $GLOBALS['wordpress_temp_file'], serialize( $data ) );
                }
                echo $data['content'];
        }
        register_shutdown_function('wordpress_shutdown');
}
// run your resource intensive stuff here... 
echo "Hello!";