kubernetes/vendor/go.etcd.io/etcd/server/v3/etcdserver/api/v2store/event_history.go

type EventHistory …

func newEventHistory(capacity int) *EventHistory { … }

// addEvent function adds event into the eventHistory
func (eh *EventHistory) addEvent(e *Event) *Event { … }

// scan enumerates events from the index history and stops at the first point
// where the key matches.
func (eh *EventHistory) scan(key string, recursive bool, index uint64) (*Event, *v2error.Error) { … }

// clone will be protected by a stop-world lock
// do not need to obtain internal lock
func (eh *EventHistory) clone() *EventHistory { … }