History when a new subscriber joins

General
1

Hi team, apologies if this has been asked before somewhere else.

I am trying to use the history on the pubsub channels. From what I can see the history with the given size is sent to a joining subscriber only when the publisher publishes a new message.

Is there any way to make the subscriber receive or request the history when it joins the topic? I’m basically trying to achieve state sync by replaying some portion of the history

Is this the recommended way to do it with your library?
Could I call update_connections in a loop from the publisher side or that is an anti-pattern?

Thanks!

2

Calling update_connections in a loop is one way but you can combine this with the event messaging pattern. The idea is, whenever a new subscriber connects and it requires the history, it sends a notification to the publisher process. When it wakes up, it calls update_connections.

You can embedded this easily in your current loop when you have a publisher where you send a sample every second for instance.

It could look a bit like:

loop {
  listener.timed_wait(|_| {
      my_publisher.update_connections(); 
    }, 
    Duration::from_secs(1))?;
}

The basic event example is explained here: iceoryx2/examples/rust/event at main · eclipse-iceoryx/iceoryx2 · GitHub

If you are interested in our vision on how to combine events with pubsub fully, you can take a look at: iceoryx2/examples/rust/event_based_communication at main · eclipse-iceoryx/iceoryx2 · GitHub

This example sends out an event whenever:

  • a new publisher joined
  • a new subscriber joined
  • a publisher sent a sample
  • a subscriber consumed a sample