xds: deletion only to watchers of same control plane

[temawi]

When XdsClient learns that a control plane no longer tracks a resource, it should only notify watchers associated with that control plane.

This matters in control plane federation cases when more than one control plane is in use.

[ejona86]

The test takes 12.5 s on my machine. That isn't the deletion detection timer. It looks to be the control plane shutdown awaitTermination. Because you neither unregister the watches not shutdown the xdsClient, xdsClient still has an ADS stream to the fake control planes so you pay 2*5 seconds. The remaining 2.5s may just be classloading.

[YifeiZhuang]

Do we know that the two control planes will never use the same resource names among all resource types? To allow for it, we ultimately need to have different subscribers for the same name but different control planes.

[ejona86]

Do we know that the two control planes will never use the same resource names among all resource types?

Well, we are the one that requests resources by names from a particular control plane. So the initial resources (listeners) would definitely have to have different xdstp authorities, otherwise we'd just talk to one control plane. When a listener references other resources, we use the authority of that resource which is totally allowed to be a different server. That allows servers to delegate to one other.