Global EventBus in GoLang

Issue

I am trying to learn GO and in doing so trying different concepts. Right now I am trying a PubSub approach, but within the application. I have an EventBus and I amd trying to pass the instance via Dependency Injection. However when I run the application nothing happens.

main

package main

import (
    "github.com/asaskevich/EventBus"
    modelA "interfaces/internal/modelA"
    modelB "interfaces/internal/modelB"
)

func main() {
    bus := EventBus.New()

    a := &modelA.Bus{EventBus: bus}
    a.Send()

    b := &modelB.Bus{
        EventBus: bus,
    }
    b.Receive()

}

internal/modelA

package modelA

import (
    "fmt"
    "github.com/asaskevich/EventBus"
)

type Bus struct {
    EventBus EventBus.Bus
}

type ModelAService interface {
    Run()
    Send()
}

func calculator(a int, b int) {
    fmt.Printf("ModelA "+"%d\n", a+b)
}

func (bus *Bus) Receive() {
    err := bus.EventBus.Subscribe("testMessageFromB", calculator)
    if err != nil {
        fmt.Printf("Error Receiving message...")
    }
}

func (bus *Bus) Send() {
    bus.EventBus.Publish("testMessageFromA", 33, 33)
}

internal/modelB

package modelB

import (
    "fmt"
    "github.com/asaskevich/EventBus"
)

type Bus struct {
    EventBus EventBus.Bus
}

type ModelBService interface {
    Run()
    Send()
}

func calculator(a int, b int) {
    fmt.Printf("ModelB "+"%d\n", a+b)
}

func (bus *Bus) Receive() {
    err := bus.EventBus.Subscribe("testMessageFromA", calculator)
    if err != nil {
        fmt.Printf("Error Receiving message...")
    }
}

func (bus *Bus) Send() {
    bus.EventBus.Publish("testMessageFromB", 33, 60)
}

Solution

You need to first Subscribe to a topic
then Publish (executes callback defined for a topic).

Try something like this:

func main() {
    bus := EventBus.New()

    a := &modelA.Bus{EventBus: bus}
    b := &modelB.Bus{EventBus: bus}

    b.Receive() // Subscribe
    a.Send()    // Publish
    // Unsubscribe
}

Also see the example:

func calculator(a int, b int) {
    fmt.Printf("%d\n", a + b)
}

func main() {
    bus := EventBus.New();
    bus.Subscribe("main:calculator", calculator);
    bus.Publish("main:calculator", 20, 40);
    bus.Unsubscribe("main:calculator", calculator);
}

My debugging structure and output:

---

Footnotes:
You may rename b.Receive() to b.Subscribe()
and a.Send() to a.Publish() for clarity.

See also gRPC:

Answered By – wasmup

Answer Checked By – Robin (GoLangFix Admin)