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

type watcherHub …

// newWatchHub creates a watcherHub. The capacity determines how many events we will
// keep in the eventHistory.
// Typically, we only need to keep a small size of history[smaller than 20K].
// Ideally, it should smaller than 20K/s[max throughput] * 2 * 50ms[RTT] = 2000
func newWatchHub(capacity int) *watcherHub { … }

// Watch function returns a Watcher.
// If recursive is true, the first change after index under key will be sent to the event channel of the watcher.
// If recursive is false, the first change after index at key will be sent to the event channel of the watcher.
// If index is zero, watch will start from the current index + 1.
func (wh *watcherHub) watch(key string, recursive, stream bool, index, storeIndex uint64) (Watcher, *v2error.Error) { … }

func (wh *watcherHub) add(e *Event) { … }

// notify function accepts an event and notify to the watchers.
func (wh *watcherHub) notify(e *Event) { … }

func (wh *watcherHub) notifyWatchers(e *Event, nodePath string, deleted bool) { … }

// clone function clones the watcherHub and return the cloned one.
// only clone the static content. do not clone the current watchers.
func (wh *watcherHub) clone() *watcherHub { … }

// isHidden checks to see if key path is considered hidden to watch path i.e. the
// last element is hidden or it's within a hidden directory
func isHidden(watchPath, keyPath string) bool { … }