mule/notifiers/pg

A process-groups notifier over Distributed Erlang — a port of Oban.Notifiers.PG (notifiers/pg.ex). Scales better than the Postgres notifier and needs no database round-trip, but lacks its transactional guarantees and requires a functional Distributed Erlang cluster (on a single unclustered node it degrades gracefully to a local-only notifier — useful for tests, pointless in production).

Every PG notifier in the cluster joins one pg group per namespace; notify sends the notification to EVERY member (its own actor included), and each member relays to its local subscribers. Like Elixir, the default namespace is shared (“public”, the port’s fixed prefix), so ALL instances in the cluster hear each other — pass Namespace to isolate a cluster of instances without renaming them.

Divergence (parity §9): members exchange the TYPED Notification term directly rather than Elixir’s JSON-ish maps — every node must run this library (Elixir-interop remains out of scope), and in return there is no codec to drift. The namespace is a String where Elixir allows any term.

pub type Message {
  Listen(
    channel: notifier.Channel,
    subscriber: process.Subject(notifier.Notification),
  )
  Unlisten(
    channel: notifier.Channel,
    subscriber: process.Subject(notifier.Notification),
  )
  Notify(notification: notifier.Notification)
  Relay(notification: notifier.Notification)
  SubscriberDown(down: process.Down)
}

pub type State {
  State(
    namespace: String,
    subscribers: dict.Dict(
      notifier.Channel,
      set.Set(process.Subject(notifier.Notification)),
    ),
    monitors: dict.Dict(process.Pid, process.Monitor),
  )
}

pub fn child(
  name name: process.Name(Message),
) -> supervision.ChildSpecification(Nil)

pub fn child_in_namespace(
  name name: process.Name(Message),
  namespace namespace: String,
) -> supervision.ChildSpecification(Nil)

pub const default_namespace: String

pub fn new(
  subject: process.Subject(Message),
) -> notifier.Notifier

pub fn start(
  namespace namespace: String,
) -> Result(
  actor.Started(process.Subject(Message)),
  actor.StartError,
)

pub fn start_named(
  name name: process.Name(Message),
  namespace namespace: String,
) -> Result(
  actor.Started(process.Subject(Message)),
  actor.StartError,
)