Potential deadlock due to calling callbacks while holding a lock

[sergey-shambir]

See golang mutexes aren't recursive / re-entrant

Bus.Publish(...) method locks mutex and calls callbacks under lock, so any access to the bus in callback will cause deadlock.

The following example reproduces issue:

package main

import (
	"fmt"

	"github.com/asaskevich/EventBus"
)

var bus EventBus.Bus

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

	if a == 20 {
		bus.Publish("main:calculator", a+1, b)
	}
}

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

We use another implementation of eventbus (inspired by yours) where this issue was fixed: github.com/ispringteam/goeventbus (see copySubscriptions method and nextID field)

Feel free to adapt our solution or introduce another one ;)

[alielbashir]

Thanks for this, i've been struggling with this lib for real time updates with gRPC streaming and faced many bugs related to unsubscribe. Moving to your implementation seems to fix the problem