Shared streams: Allow subscribing after reflector is created

[howardjohn]

Would you like to work on this feature?

maybe

What problem are you trying to solve?

I would like to subscribe to a shared stream after a reflector is created. Unlike the example here, I do not know ahead of times how many times I will need to subscribe, and I may want to subscribe later on in the process (for instance, after I win leader election for a subcontroller).

This is how client-go informers behave, for instance, which can register multiple event handlers dynamically. Note they can also de-register them, which his something we may need to consider (presumably by Dropping them?)

Describe the solution you'd like

Either reflect_shared returns an object (not impl stream) that can subscribe(), reflect_shared doesn't take ownership of Writer, or writer has a fn get_subscriber(&self) -> ThingICanCallSubscriberOn

Describe alternatives you've considered

Build my own abstraction on top. This is tricky because we need the ability for the stream to consist of [objects that already exist,..., new events coming in after we started].

In theory you could do this by doing store.state() and getting the initial snapshot, then adding any updates after that. However, there is a race condition here. client-go does this, but they are able to lock the primary stream/store while they do this.

Documentation, Adoption, Migration Strategy

No response

Target crate for feature

kube-runtime