func (fum *FakeUnitManager) GetUnitStates(filter pkg.Set) (map[string]*UnitState, error) {
	fum.RLock()
	defer fum.RUnlock()

	states := make(map[string]*UnitState)
	for _, name := range filter.Values() {
		if _, ok := fum.u[name]; ok {
			states[name] = &UnitState{"loaded", "active", "running", "", "", name}
		}
	}

	return states, nil
}

func (m *systemdUnitManager) GetUnitStates(filter pkg.Set) (map[string]*unit.UnitState, error) {
	// Unfortunately we need to lock for the entire operation to ensure we
	// have a consistent view of the hashes. Otherwise, Load/Unload
	// operations could mutate the hashes before we've retrieved the state
	// for every unit in the filter, since they won't necessarily all be
	// present in the initial ListUnits() call.
	m.mutex.Lock()
	defer m.mutex.Unlock()
	dbusStatuses, err := m.systemd.ListUnits()

	if err != nil {
		return nil, err
	}

	states := make(map[string]*unit.UnitState)
	for _, dus := range dbusStatuses {
		if !filter.Contains(dus.Name) {
			continue
		}

		us := &unit.UnitState{
			LoadState:   dus.LoadState,
			ActiveState: dus.ActiveState,
			SubState:    dus.SubState,
		}
		if h, ok := m.hashes[dus.Name]; ok {
			us.UnitHash = h.String()
		}
		states[dus.Name] = us
	}

	// grab data on subscribed units that didn't show up in ListUnits, most
	// likely due to being inactive
	for _, name := range filter.Values() {
		if _, ok := states[name]; ok {
			continue
		}

		us, err := m.getUnitState(name)
		if err != nil {
			return nil, err
		}
		if h, ok := m.hashes[name]; ok {
			us.UnitHash = h.String()
		}
		states[name] = us
	}

	return states, nil
}

func (ar *AgentReconciler) calculateTasksForOffer(dState *agentState, ms *machine.MachineState, j *job.Job, bids pkg.Set, taskchan chan *task) {
	if bids.Contains(ms.ID) {
		log.V(1).Infof("Bid already submitted for unresolved JobOffer(%s)", j.Name)
		return
	}

	if able, reason := ar.ableToRun(dState, ms, j); !able {
		log.V(1).Infof("Not bidding on Job(%s): %s", j.Name, reason)
		return
	}

	taskchan <- &task{
		Type:   taskTypeSubmitBid,
		Job:    j,
		Reason: taskReasonAbleToResolveOffer,
	}
}

// Generate returns and fills a channel with *UnitStateHeartbeat objects. Objects will
// only be returned for units to which this generator is currently subscribed.
func (g *UnitStateGenerator) Generate() (<-chan *UnitStateHeartbeat, error) {
	var lastSubscribed pkg.Set
	if g.lastSubscribed != nil {
		lastSubscribed = g.lastSubscribed.Copy()
	}

	subscribed := g.subscribed.Copy()
	g.lastSubscribed = subscribed

	reportable, err := g.mgr.GetUnitStates(subscribed)
	if err != nil {
		return nil, err
	}

	beatchan := make(chan *UnitStateHeartbeat)
	go func() {
		for name, us := range reportable {
			us := us
			beatchan <- &UnitStateHeartbeat{
				Name:  name,
				State: us,
			}
		}

		if lastSubscribed != nil {
			// For all units that were part of the subscription list
			// last time Generate ran, but are now not part of that
			// list, send nil-State heartbeats to signal removal
			for _, name := range lastSubscribed.Sub(subscribed).Values() {
				beatchan <- &UnitStateHeartbeat{
					Name: name,
				}
			}
		}

		close(beatchan)
	}()

	return beatchan, nil
}

func (m *systemdUnitManager) GetUnitStates(filter pkg.Set) (map[string]*unit.UnitState, error) {
	// Unfortunately we need to lock for the entire operation to ensure we
	// have a consistent view of the hashes. Otherwise, Load/Unload
	// operations could mutate the hashes before we've retrieved the state
	// for every unit in the filter, since they won't necessarily all be
	// present in the initial ListUnits() call.
	fallback := false

	m.mutex.Lock()
	defer m.mutex.Unlock()
	dbusStatuses, err := m.systemd.ListUnitsByNames(filter.Values())

	if err != nil {
		fallback = true
		log.Debugf("ListUnitsByNames is not implemented in your systemd version (requires at least systemd 230), fallback to ListUnits: %v", err)
		dbusStatuses, err = m.systemd.ListUnits()
		if err != nil {
			return nil, err
		}
	}

	states := make(map[string]*unit.UnitState)
	for _, dus := range dbusStatuses {
		if fallback && !filter.Contains(dus.Name) {
			// If filter could not be applied on DBus side, we will filter unit files here
			continue
		}

		us := &unit.UnitState{
			LoadState:   dus.LoadState,
			ActiveState: dus.ActiveState,
			SubState:    dus.SubState,
		}
		if h, ok := m.hashes[dus.Name]; ok {
			us.UnitHash = h.String()
		}
		states[dus.Name] = us
	}

	// grab data on subscribed units that didn't show up in ListUnits in fallback mode, most
	// likely due to being inactive
	if fallback {
		for _, name := range filter.Values() {
			if _, ok := states[name]; ok {
				continue
			}

			us, err := m.getUnitState(name)
			if err != nil {
				return nil, err
			}
			if h, ok := m.hashes[name]; ok {
				us.UnitHash = h.String()
			}
			states[name] = us
		}
	}

	return states, nil
}