raft/read_only.go
func (ro *readOnly) lastPendingRequestCtx() string {
	if len(ro.readIndexQueue) == 0 {
		return ""
	}
	return ro.readIndexQueue[len(ro.readIndexQueue)-1]
}
func (ro *readOnly) lastPendingRequestCtx() string {
	if len(ro.readIndexQueue) == 0 {
		return ""
	}
	return ro.readIndexQueue[len(ro.readIndexQueue)-1]
}
// lastPendingRequestCtx returns the context of the last pending read only
// request in readonly struct.