But that still doesn't really solve the whole progress reporting part of it. As per my example, the "job" would really be 20 individual cropping/resizing jobs. In order to know that the whole set of jobs is complete, there needs to be a checking job or something similar that looks to see out of the total number of jobs started, if all are now completed, and if so, tell the user.
Is there a pattern for that type of situation? Some sort of watcher pattern or master job monitoring pattern that allows accurate progress reporting?
Send progress events over your push channel. Push an event every 1% or 10% or whatever you need depending on what you need for your experience.
If you're talking about generic progress reporting from a tool that doesn't know what the underlying job consists of (i.e. it only knows "started" "done" "errored"), then I'm not aware of any pattern to provide an accurate progress meter. You could perhaps keep statistics on the length of past runs (like some CI servers do for build times), but it would really depend on your application whether users are willing to accept that those progress bars are just a guess and sometimes run over.
Is there a pattern for that type of situation? Some sort of watcher pattern or master job monitoring pattern that allows accurate progress reporting?