Clarification on "periodic task" processor

[Russell Bateman]

I'm doing something I've never done before in a custom processor. I'm 
writing a processor that will awaken every /n/ minutes, query a 
database, perform work as indicated by the result of the query, then go 
back to sleep for /n/ minutes.

This processor will never expect a flowfile because it doesn't work on 
flowfile attributes or content. It may, I think, emit some flowfiles 
downstream.

Will onTrigger()be called without a flowfile? That point seems unclear 
in the Developer Guide. Or is there some other lifecycle, like 
@OnScheduledthat I should expect to use for this?

Thanks,

Russ