Simple bus implementation

[ziollek]

Introduction

I've prepared a simplified implementation of an event bus that exposes interfaces very similar to those of the original Bus. This eliminates the need to use reflection in Publish.

Why?

The main goal was to provide a more efficient solution that does not rely entirely on reflection. However, this approach comes with limitations related to how generic types are handled in Go. Specifically, it allows subscribing with callbacks that accept only a single parameter of the type associated with a particular instance of SimpleBus.

How to use it

func main() {
	bus := EventBus.NewSimpleBus[string]()
	ref := bus.Subscribe("topic", func(arg string) {
		fmt.Printf("Hello %s!\n", arg)
	})
	bus.Publish("topic", "world")
        bus.Unsubscribe("topic", ref)
}

Key differences:

• Subscription methods do not return errors since type safety is ensured by Go, they return SubscriptionRef that allow Unsubscribe without engaging reflection
• When calling Publish, there is no lock held for the entire duration of executing listener callbacks.

if subscribers, ok := bus.fetchSubscribers(topic); ok {
	fire := make(chan *genericHandler[T], len(*subscribers))
	bus.Lock()
	for _, subscriber := range *subscribers {
		fire <- subscriber
		if subscriber.once {
			bus.handlers[topic].delete(subscriber)
		}
	}
	bus.Unlock()
	close(fire)
	// calling the callbacks will not block the whole bus
	for subscriber := range fire {
		subscriber.Call(arg, &bus.wg)
	}
}

Performance analysis

To simplify performance comparisons, benchmarks have been added to the test files. Below are the results from my workstation:

Benchmark using a single core:

% GOMAXPROCS=1 go test -bench=.
2
goos: darwin
goarch: amd64
pkg: github.com/ziollek/EventBus
cpu: Intel(R) Core(TM) i7-9750H CPU @ 2.60GHz
BenchmarkSynchronousPublishing        	 2877297	       406.9 ns/op
BenchmarkAsynchronousPublishing       	  548457	      2101 ns/op
BenchmarkSimpleSynchronousPublishing  	 3939492	       305.5 ns/op
BenchmarkSimpleAsynchronousPublishing 	 1000000	      1141 ns/op

Benchmark using a two cores:

GOMAXPROCS=2 go test -bench=.
2
goos: darwin
goarch: amd64
pkg: github.com/ziollek/EventBus
cpu: Intel(R) Core(TM) i7-9750H CPU @ 2.60GHz
BenchmarkSynchronousPublishing-2          	 3146671	       379.3 ns/op
BenchmarkAsynchronousPublishing-2         	 1050337	      1148 ns/op
BenchmarkSimpleSynchronousPublishing-2    	 5079916	       246.0 ns/op
BenchmarkSimpleAsynchronousPublishing-2   	 2124786	       548.2 ns/op

[asaskevich]

Hi, @ziollek! Thank you! I'll take a look into it and merge once I'm done