func isCompatibleWithVers(vers map[string]*version.Versions, local types.ID, minV, maxV *semver.Version) bool {
	var ok bool
	for id, v := range vers {
		// ignore comparasion with local version
		if id == local.String() {
			continue
		}
		if v == nil {
			continue
		}
		clusterv, err := semver.NewVersion(v.Cluster)
		if err != nil {
			plog.Errorf("cannot understand the cluster version of member %s (%v)", id, err)
			continue
		}
		if clusterv.LessThan(*minV) {
			plog.Warningf("the running cluster version(%v) is lower than the minimal cluster version(%v) supported", clusterv.String(), minV.String())
			return false
		}
		if maxV.LessThan(*clusterv) {
			plog.Warningf("the running cluster version(%v) is higher than the maximum cluster version(%v) supported", clusterv.String(), maxV.String())
			return false
		}
		ok = true
	}
	return ok
}

func (c *cluster) SetVersion(ver *semver.Version) {
	c.Lock()
	defer c.Unlock()
	if c.version != nil {
		plog.Noticef("updated the cluster version from %v to %v", c.version.String(), ver.String())
	} else {
		plog.Noticef("set the initial cluster version to %v", ver.String())
	}
	c.version = ver
}

// capabilityLoop checks the cluster version every 500ms and updates
// the enabledCapability when the cluster version increased.
// capabilityLoop MUST be ran in a goroutine before checking capability
// or using capabilityHandler.
func capabilityLoop(s *etcdserver.EtcdServer) {
	stopped := s.StopNotify()

	var pv *semver.Version
	for {
		if v := s.ClusterVersion(); v != pv {
			if pv == nil {
				pv = v
			} else if v != nil && pv.LessThan(*v) {
				pv = v
			}
			enableMapMu.Lock()
			enabledMap = capabilityMaps[pv.String()]
			enableMapMu.Unlock()
		}

		select {
		case <-stopped:
			return
		case <-time.After(500 * time.Millisecond):
		}
	}
}

func MustDetectDowngrade(cv *semver.Version) {
	lv := semver.Must(semver.NewVersion(version.Version))
	// only keep major.minor version for comparison against cluster version
	lv = &semver.Version{Major: lv.Major, Minor: lv.Minor}
	if cv != nil && lv.LessThan(*cv) {
		plog.Fatalf("cluster cannot be downgraded (current version: %s is lower than determined cluster version: %s).", version.Version, version.Cluster(cv.String()))
	}
}