A PubSub solution for LabVIEW Actors.
This is a demo as a proof-of-concept. Better dont use it in production code.
Ever got tired of the quirks of keeping references to your actors enqueuers up to date, know which reference can accept which messages and these awful race-conditions in the initialization process of multiple actors (Frontpanels...)? I was... so I implemented some kind of PubSub-like helper that allows to add actors to topics and send messages to topics.
These topics may simple be strings, but -more interstingly- may also be interfaces. So you can simply send a message related to an interface some of your actors implement to the channel associated to this interface. As the sender, you can do nothing wrong. You simply have to make sure, that your actors subscribe to the interfaces they implement. Even better: It doesn't matter if the sender or the reciever comes up first. And subscriptions can be made and rejected anytime in runtime.
You can even retain messages, eleminating race-conditions during startup of actors. And you can create a channel that pushes serialized messages over MQTT. Or you could create your own load-balancing channels... Or a /dev/null channel if you like... Or you can subscribe a channel to all other channels, that logs your messages...
The biggest impact nevertheless is the ability to create zero-coupled extensions and plugins, using PubSub-Channels and interfaces. This way, neither the sender(s) nor the receiver(s) have to know anything of the other side
I use this concept in a big application with ~15 actors and ~50 channels with great performance. This project is an affort to extract this concept in a package.
You can simply clone and try this repo. For installation, download the VIP packages from Releases and install them using VIPM.
Subscribe your actor anytime from a method of the actor (usually in "Actor Core" or "Pre Launch Init") to a topic either given by a string id or by a class / interface:
Send a message (publish) to the topic channel anywhere, anytime:
Unsubscribe the actor anytime or when it stops. If no subscribers are left, the channel will close.
Look at the provided examples ("Simple Chat")!
Every channel has its own message queue and runs asynchronously. It keeps track of the subscribed actors (identified by their enqueuer). When a message is dequeued, copies of it are sent to every subscribed enqueuer, if it matches the given filters of the channel (if any). The management of the channels and their assoicited topics is done using a single VI, which is wrapped by some helpers. This way, no references need to be passed, everything is stored in the non-reentrant registry, which is associated to the application instance.
As another proof-of-concept, I added a MQTT channel. This uses mqtt as its backend, allowing multiple instances to communicate with each other. You can try this by compiling the binary and run the demo from the IDE as well.
MQTT Client (For the mqtt channel only)