added default hwm and per-subscriber queues

wyang5 commented 4 months ago

Hey! I'm a fan of this library. A couple of tweaks:

Default high-water mark:
- The HWM is currently set to zero, which allows the queue to grow infinitely - https://github.com/go-zeromq/zmq4/issues/151.
- The spec states that we "SHOULD constrain queue sizes to a runtime-configurable limit". In libzmq, the default is 1000, so that seemed like a sensible choice. Side note, there was a TODO to allow for "per subscriber hwm". The zmq docs are a bit vague in some places but it seems like it's supposed to be per-socket rather than per-subscriber.
- This allows us to use Go's buffered channels instead of Queue.
Per-subscriber queues:
- Currently, the pub socket maintains a single outbound queue, which can cause issues (e.g. what happens if a single connection hangs?)
- Instead, we can spawn a goroutine for each Conn added. This also address this TODO.
- Again looking at the spec: we "SHALL maintain a single outgoing message queue for each connected subscriber".

Flixnore commented 3 months ago

Would love to see this resolved @sbinet

sbinet commented 3 months ago

sbinet commented 3 months ago

thanks for the PR and sticking with us.

go-zeromq / zmq4