proxy/grpcproxy/leader.go
func (l *leader) lostNotify() <-chan struct{} {
	l.mu.RLock()
	defer l.mu.RUnlock()
	return l.leaderc
}
func (l *leader) lostNotify() <-chan struct{} {
	l.mu.RLock()
	defer l.mu.RUnlock()
	return l.leaderc
}
// lostNotify returns a channel that is closed if there has been
// a leader loss not yet followed by a leader reacquire.