// DataChange blocks until the data of the watched Zookeeper node changes
// reltive to the returned values of the last invokation of Data or DataChange.
// It returns the new data and stat values.
func (w *Watch) DataChange(sinceStat *zookeeper.Stat, expire time.Duration) (data string, stat *zookeeper.Stat, err error) {
// Still alive?
w.lk.Lock()
z, dwatch := w.zookeeper, w.dwatch
w.lk.Unlock()
if z == nil {
return "", nil, ErrClosed
}
// Wait if watch present, otherwise read from Zookeeper
if dwatch != nil {
// If we already have a newer revision, return it
w.lk.Lock()
if sinceStat == nil || w.dstat.Version() > sinceStat.Version() {
defer w.lk.Unlock()
return w.data, w.dstat, nil
}
w.lk.Unlock()
if expire == 0 {
<-dwatch
} else {
select {
case <-dwatch:
case <-time.After(expire):
return "", nil, ErrExpire
}
}
}
return w.fetchData()
}
