Signal for other processes when Monstache is done with direct reads

[DagW]

Hello! We would like to automate the handling of indices and their sync state,
for example swithing to use a new index once Monstache is done with direct reads and switch to following updates - marking the index as "up to date" and ready to use.

I think it can be done from our other process if the stateful direct read is written when its completed, instead of at shutdown.
Suggestion: #682

Is there any other strategy?

Thanks for Monstache by the way! Super useful