lib's event implement have some flaw

[goolAdapter]

This issue doesn't exist in the current runtime, but as an base lib, I think it's better to more robust.

Lib event designed for multi routine, but AddListenerForEvent and RemoveListener manipulate listener and eventCell in different order.

tendermint/libs/events/events.go

Lines 76 to 78 in 0c9c329

	// Add event and listener
	eventCell.AddListener(listenerID, cb)
	listener.AddEvent(event)

tendermint/libs/events/events.go

Lines 94 to 98 in 0c9c329

	// Remove callback for each event.
	listener.SetRemoved()
	for _, event := range listener.GetEvents() {
	evsw.RemoveListenerForEvent(event, listenerID)
	}

consider two routine，A call AddListenerForEvent and B call RemoveListener simultaneous.

B -> listener.SetRemoved()
A -> eventCell.AddListener(listenerID, cb)
A -> listener.AddEvent(event)
B -> for _, event := range listener.GetEvents() {
		evsw.RemoveListenerForEvent(event, listenerID)
}

At this time, Listener added by A will not be clean up. the fix is to try AddEvent first, only when AddEvent succeeded, eventCell can AddListener.

by the way，eventCell.FireEvent is easy to deadlock, as lock's range is uncontrollable when run callback.

tendermint/libs/events/events.go

Lines 169 to 175 in 0c9c329

	func (cell *eventCell) FireEvent(data EventData) {
	cell.mtx.RLock()
	for _, listener := range cell.listeners {
	listener(data)
	}
	cell.mtx.RUnlock()
	}

[melekes]

note: we'll get rid of the events package in #1692

[xla]

Merged to develop.