folly::Observer

folly::Observer

Summary:
This is a basic implementation of a new Observer API. I mostly see this being useful as a replacement for various configuration subscription APIs (Configerator, SMC etc.)

The library provides an Observer primitive. At any time user can take a Snapshot of data in the Observer (which is a view with the most recent version of the data). New Observer can be created by providing a generator functor. Such Observer mays depend on other Observers and its generator functor is re-run automatically every time, when at least one of the dependencies are updated. The implementation may also ignore intermediate updates and will only use the most recent version of other Observers, when re-computing Observer data.

Reviewed By: yfeldblum

Differential Revision: D3481231

fbshipit-source-id: 96c165f8081cff0141d5814ec2bc88adeb2e1e74