Many queueing systems (such as ActiveMQ, Beanstalkd etc) allow items to be given a priority when they are added to a queue, in order to allow applications to determine whether an item should be processed before others. The original issue to get queue API into D7 (http://drupal.org/node/391340) stated:
Queue cleanup and priorities are not yet there -- there is always a next, patch.
Therefore, this issue proposes a patch to the core queue API, allowing createItem() to set a priority. It exposes this in the Database Queue implementation, with priority used as an additional parameter to sort items by when claiming.
No change has so far been made to the MemoryQueue implementation, although this should also be considered.
First aim is to get a change in which is transparent and allows all existing tests to pass, a follow up will add tests to test that the queue prioritisation has the desired effect but I wanted to get views on the change before progressing.