// watchStorageAttachment starts watching the storage attachment with
// the specified storage tag, waits for its first event, and records
// the information in the current snapshot.
func (w *RemoteStateWatcher) watchStorageAttachment(
	tag names.StorageTag,
	life params.Life,
	in apiwatcher.NotifyWatcher,
) error {
	var storageSnapshot StorageSnapshot
	select {
	case <-w.tomb.Dying():
		return tomb.ErrDying
	case _, ok := <-in.Changes():
		if !ok {
			return watcher.EnsureErr(in)
		}
		var err error
		storageSnapshot, err = getStorageSnapshot(w.st, tag, w.unit.Tag())
		if params.IsCodeNotProvisioned(err) {
			// If the storage is unprovisioned, we still want to
			// record the attachment, but we'll mark it as
			// unattached. This allows the uniter to wait for
			// pending storage attachments to be provisioned.
			storageSnapshot = StorageSnapshot{Life: life}
		} else if err != nil {
			return errors.Annotatef(err, "processing initial storage attachment change")
		}
	}
	w.current.Storage[tag] = storageSnapshot
	w.storageAttachmentWatchers[tag] = newStorageAttachmentWatcher(
		w.st, in, w.unit.Tag(), tag, w.storageAttachmentChanges,
	)
	return nil
}

// watchForProxyChanges kicks off a go routine to listen to the watcher and
// update the proxy settings.
func (u *Uniter) watchForProxyChanges(environWatcher apiwatcher.NotifyWatcher) {
	go func() {
		for {
			select {
			case <-u.tomb.Dying():
				return
			case _, ok := <-environWatcher.Changes():
				logger.Debugf("new environment change")
				if !ok {
					return
				}
				environConfig, err := u.st.EnvironConfig()
				if err != nil {
					logger.Errorf("cannot load environment configuration: %v", err)
				} else {
					u.updatePackageProxy(environConfig)
				}
			}
		}
	}()
}

// WaitForEnviron waits for an valid environment to arrive from
// the given watcher. It terminates with tomb.ErrDying if
// it receives a value on dying.
func WaitForEnviron(w apiwatcher.NotifyWatcher, st EnvironConfigGetter, dying <-chan struct{}) (environs.Environ, error) {
	for {
		select {
		case <-dying:
			return nil, tomb.ErrDying
		case _, ok := <-w.Changes():
			if !ok {
				return nil, watcher.EnsureErr(w)
			}
			config, err := st.EnvironConfig()
			if err != nil {
				return nil, err
			}
			environ, err := environs.New(config)
			if err == nil {
				return environ, nil
			}
			logger.Errorf("loaded invalid environment configuration: %v", err)
			loadedInvalid()
		}
	}
}

func (w *storageprovisioner) loop() error {
	var environConfigChanges <-chan struct{}
	var volumesWatcher apiwatcher.StringsWatcher
	var filesystemsWatcher apiwatcher.StringsWatcher
	var volumesChanges <-chan []string
	var filesystemsChanges <-chan []string
	var volumeAttachmentsWatcher apiwatcher.MachineStorageIdsWatcher
	var filesystemAttachmentsWatcher apiwatcher.MachineStorageIdsWatcher
	var volumeAttachmentsChanges <-chan []params.MachineStorageId
	var filesystemAttachmentsChanges <-chan []params.MachineStorageId
	var machineBlockDevicesWatcher apiwatcher.NotifyWatcher
	var machineBlockDevicesChanges <-chan struct{}
	machineChanges := make(chan names.MachineTag)

	environConfigWatcher, err := w.environ.WatchForEnvironConfigChanges()
	if err != nil {
		return errors.Annotate(err, "watching environ config")
	}
	defer watcher.Stop(environConfigWatcher, &w.tomb)
	environConfigChanges = environConfigWatcher.Changes()

	// Machine-scoped provisioners need to watch block devices, to create
	// volume-backed filesystems.
	if machineTag, ok := w.scope.(names.MachineTag); ok {
		machineBlockDevicesWatcher, err = w.volumes.WatchBlockDevices(machineTag)
		if err != nil {
			return errors.Annotate(err, "watching block devices")
		}
		defer watcher.Stop(machineBlockDevicesWatcher, &w.tomb)
		machineBlockDevicesChanges = machineBlockDevicesWatcher.Changes()
	}

	// The other watchers are started dynamically; stop only if started.
	defer w.maybeStopWatcher(volumesWatcher)
	defer w.maybeStopWatcher(volumeAttachmentsWatcher)
	defer w.maybeStopWatcher(filesystemsWatcher)
	defer w.maybeStopWatcher(filesystemAttachmentsWatcher)

	startWatchers := func() error {
		var err error
		volumesWatcher, err = w.volumes.WatchVolumes()
		if err != nil {
			return errors.Annotate(err, "watching volumes")
		}
		filesystemsWatcher, err = w.filesystems.WatchFilesystems()
		if err != nil {
			return errors.Annotate(err, "watching filesystems")
		}
		volumeAttachmentsWatcher, err = w.volumes.WatchVolumeAttachments()
		if err != nil {
			return errors.Annotate(err, "watching volume attachments")
		}
		filesystemAttachmentsWatcher, err = w.filesystems.WatchFilesystemAttachments()
		if err != nil {
			return errors.Annotate(err, "watching filesystem attachments")
		}
		volumesChanges = volumesWatcher.Changes()
		filesystemsChanges = filesystemsWatcher.Changes()
		volumeAttachmentsChanges = volumeAttachmentsWatcher.Changes()
		filesystemAttachmentsChanges = filesystemAttachmentsWatcher.Changes()
		return nil
	}

	ctx := context{
		scope:                             w.scope,
		storageDir:                        w.storageDir,
		volumeAccessor:                    w.volumes,
		filesystemAccessor:                w.filesystems,
		life:                              w.life,
		machineAccessor:                   w.machines,
		statusSetter:                      w.status,
		time:                              w.clock,
		volumes:                           make(map[names.VolumeTag]storage.Volume),
		volumeAttachments:                 make(map[params.MachineStorageId]storage.VolumeAttachment),
		volumeBlockDevices:                make(map[names.VolumeTag]storage.BlockDevice),
		filesystems:                       make(map[names.FilesystemTag]storage.Filesystem),
		filesystemAttachments:             make(map[params.MachineStorageId]storage.FilesystemAttachment),
		machines:                          make(map[names.MachineTag]*machineWatcher),
		machineChanges:                    machineChanges,
		schedule:                          schedule.NewSchedule(w.clock),
		pendingVolumeBlockDevices:         make(set.Tags),
		incompleteVolumeParams:            make(map[names.VolumeTag]storage.VolumeParams),
		incompleteVolumeAttachmentParams:  make(map[params.MachineStorageId]storage.VolumeAttachmentParams),
		pendingFilesystems:                make(map[names.FilesystemTag]storage.FilesystemParams),
		pendingFilesystemAttachments:      make(map[params.MachineStorageId]storage.FilesystemAttachmentParams),
		pendingDyingFilesystemAttachments: make(map[params.MachineStorageId]storage.FilesystemAttachmentParams),
	}
	ctx.managedFilesystemSource = newManagedFilesystemSource(
		ctx.volumeBlockDevices, ctx.filesystems,
	)
	defer func() {
		for _, w := range ctx.machines {
			w.stop()
		}
	}()

	for {
		// Check if any pending operations can be fulfilled.
		if err := processPending(&ctx); err != nil {
			return errors.Trace(err)
//.........这里部分代码省略.........

func (f *filter) loop(unitTag string) (err error) {
	// TODO(dfc) named return value is a time bomb
	defer func() {
		if params.IsCodeNotFoundOrCodeUnauthorized(err) {
			err = worker.ErrTerminateAgent
		}
	}()
	tag, err := names.ParseUnitTag(unitTag)
	if err != nil {
		return err
	}
	if f.unit, err = f.st.Unit(tag); err != nil {
		return err
	}
	if err = f.unitChanged(); err != nil {
		return err
	}
	f.service, err = f.unit.Service()
	if err != nil {
		return err
	}
	if err = f.serviceChanged(); err != nil {
		return err
	}
	unitw, err := f.unit.Watch()
	if err != nil {
		return err
	}
	defer f.maybeStopWatcher(unitw)
	servicew, err := f.service.Watch()
	if err != nil {
		return err
	}
	defer f.maybeStopWatcher(servicew)
	// configw and relationsw can get restarted, so we need to use
	// their eventual values in the defer calls.
	var configw apiwatcher.NotifyWatcher
	var configChanges <-chan struct{}
	curl, err := f.unit.CharmURL()
	if err == nil {
		configw, err = f.unit.WatchConfigSettings()
		if err != nil {
			return err
		}
		configChanges = configw.Changes()
		f.upgradeFrom.url = curl
	} else if err != uniter.ErrNoCharmURLSet {
		filterLogger.Errorf("unit charm: %v", err)
		return err
	}
	defer func() {
		if configw != nil {
			watcher.Stop(configw, &f.tomb)
		}
	}()
	actionsw, err := f.unit.WatchActions()
	if err != nil {
		return err
	}
	f.actionsPending = make([]string, 0)
	defer func() {
		if actionsw != nil {
			watcher.Stop(actionsw, &f.tomb)
		}
	}()
	relationsw, err := f.service.WatchRelations()
	if err != nil {
		return err
	}
	defer func() {
		if relationsw != nil {
			watcher.Stop(relationsw, &f.tomb)
		}
	}()
	var addressChanges <-chan struct{}
	addressesw, err := f.unit.WatchAddresses()
	if err != nil {
		return err
	}
	defer watcher.Stop(addressesw, &f.tomb)

	// Config events cannot be meaningfully discarded until one is available;
	// once we receive the initial change, we unblock discard requests by
	// setting this channel to its namesake on f.
	var discardConfig chan struct{}
	for {
		var ok bool
		select {
		case <-f.tomb.Dying():
			return tomb.ErrDying

		// Handle watcher changes.
		case _, ok = <-unitw.Changes():
			filterLogger.Debugf("got unit change")
			if !ok {
				return watcher.MustErr(unitw)
			}
			if err = f.unitChanged(); err != nil {
				return err
			}
//.........这里部分代码省略.........

func stopWatcher(c *gc.C, w apiwatcher.NotifyWatcher) {
	err := w.Stop()
	c.Check(err, jc.ErrorIsNil)
}

func (f *filter) loop(unitTag names.UnitTag) (err error) {
	// TODO(dfc) named return value is a time bomb
	defer func() {
		if params.IsCodeNotFoundOrCodeUnauthorized(err) {
			err = worker.ErrTerminateAgent
		}
	}()
	if f.unit, err = f.st.Unit(unitTag); err != nil {
		return err
	}
	if err = f.unitChanged(); err != nil {
		return err
	}
	if err = f.meterStatusChanged(); err != nil {
		return err
	}
	f.service, err = f.unit.Service()
	if err != nil {
		return err
	}
	if err = f.serviceChanged(); err != nil {
		return err
	}
	unitw, err := f.unit.Watch()
	if err != nil {
		return err
	}
	defer f.maybeStopWatcher(unitw)
	servicew, err := f.service.Watch()
	if err != nil {
		return err
	}
	defer f.maybeStopWatcher(servicew)
	// configw and relationsw can get restarted, so we need to use
	// their eventual values in the defer calls.
	var configw apiwatcher.NotifyWatcher
	var configChanges <-chan struct{}
	curl, err := f.unit.CharmURL()
	if err == nil {
		configw, err = f.unit.WatchConfigSettings()
		if err != nil {
			return err
		}
		configChanges = configw.Changes()
		f.upgradeFrom.url = curl
	} else if err != uniter.ErrNoCharmURLSet {
		filterLogger.Errorf("unit charm: %v", err)
		return err
	}
	defer f.maybeStopWatcher(configw)
	actionsw, err := f.unit.WatchActionNotifications()
	if err != nil {
		return err
	}
	f.actionsPending = make([]string, 0)
	defer f.maybeStopWatcher(actionsw)
	relationsw, err := f.service.WatchRelations()
	if err != nil {
		return err
	}
	defer f.maybeStopWatcher(relationsw)
	meterStatusw, err := f.unit.WatchMeterStatus()
	if err != nil {
		return err
	}
	defer f.maybeStopWatcher(meterStatusw)
	addressesw, err := f.unit.WatchAddresses()
	if err != nil {
		return err
	}
	defer watcher.Stop(addressesw, &f.tomb)
	storagew, err := f.unit.WatchStorage()
	if err != nil {
		return err
	}
	defer watcher.Stop(storagew, &f.tomb)
	leaderSettingsw, err := f.st.LeadershipSettings.WatchLeadershipSettings(f.service.Tag().Id())
	if err != nil {
		return err
	}
	defer watcher.Stop(leaderSettingsw, &f.tomb)

	// Ignore external requests for leader settings behaviour until we see the first change.
	var discardLeaderSettings <-chan struct{}
	var wantLeaderSettings <-chan bool
	// By default we send all leaderSettings onwards.
	sendLeaderSettings := true

	// Config events cannot be meaningfully discarded until one is available;
	// once we receive the initial config and address changes, we unblock
	// discard requests by setting this channel to its namesake on f.
	var discardConfig chan struct{}
	var seenConfigChange bool
	var seenAddressChange bool
	maybePrepareConfigEvent := func() {
		if !seenAddressChange {
			filterLogger.Debugf("no address change seen yet, skipping config event")
			return
		}
		if !seenConfigChange {
//.........这里部分代码省略.........