Is there any official doc that explain how to use the producer consumer event mechanism in dspace ? I have been looking for it but I only find a project proposal. Anything official on the matter?
There is something about the (newer) Spring-based event mechanism in the official docs: https://wiki.duraspace.org/display/DSDOC5x/DSpace+Services+Framework#DSpaceServicesFramework-EventService
I can't see any mention about the older event mechanism in the official docs other than in the configuration reference: https://wiki.duraspace.org/display/DSDOC5x/Configuration+Reference#ConfigurationReference-EventSystemConfiguration and this has a (broken) link to presumably the project proposal you have already found.
What are you trying to achieve? Perhaps someone here can walk you through your specific case and someone can distill that into useful documentation.