<?php
function register_action($action) {
  error_log(microtime(true) . "\n", 3, "/tmp/tagmy.$action");
}

function log_info($msg) {
  error_log(date("Y-m-d H:i:s") . " $msg\n", 3, "/tmp/tagmy.log.info");
}

function try_from_cache() {
  global $memcache;

  if ($memcache) {
    $img = $memcache->get(file_name());
    if ($img) {
      log_info('memcache hit for ' . file_name() . ' ' . $_SERVER["REQUEST_URI"]);
      register_action("image.cached");
      send_headers();
      echo $img;
      exit();
    } else {
      log_info('memcache miss for ' . file_name() . ' ' . $_SERVER["REQUEST_URI"]);
    }
  }
}

function do_image() {
  global $UriParts;

  try_from_cache();

  ... lots of work to make the image ...

  register_action("image.created");
}