func (u *Uniter) loop(unitTag names.UnitTag) (err error) {
	if err := u.init(unitTag); err != nil {
		if err == worker.ErrTerminateAgent {
			return err
		}
		return fmt.Errorf("failed to initialize uniter for %q: %v", unitTag, err)
	}
	logger.Infof("unit %q started", u.unit)

	// Install is a special case, as it must run before there
	// is any remote state, and before the remote state watcher
	// is started.
	var charmURL *corecharm.URL
	var charmModifiedVersion int
	opState := u.operationExecutor.State()
	if opState.Kind == operation.Install {
		logger.Infof("resuming charm install")
		op, err := u.operationFactory.NewInstall(opState.CharmURL)
		if err != nil {
			return errors.Trace(err)
		}
		if err := u.operationExecutor.Run(op); err != nil {
			return errors.Trace(err)
		}
		charmURL = opState.CharmURL
	} else {
		curl, err := u.unit.CharmURL()
		if err != nil {
			return errors.Trace(err)
		}
		charmURL = curl
		svc, err := u.unit.Service()
		if err != nil {
			return errors.Trace(err)
		}
		charmModifiedVersion, err = svc.CharmModifiedVersion()
		if err != nil {
			return errors.Trace(err)
		}
	}

	var (
		watcher   *remotestate.RemoteStateWatcher
		watcherMu sync.Mutex
	)

	logger.Infof("hooks are retried %v", u.hookRetryStrategy.ShouldRetry)
	retryHookChan := make(chan struct{}, 1)
	retryHookTimer := utils.NewBackoffTimer(utils.BackoffTimerConfig{
		Min:    u.hookRetryStrategy.MinRetryTime,
		Max:    u.hookRetryStrategy.MaxRetryTime,
		Jitter: u.hookRetryStrategy.JitterRetryTime,
		Factor: u.hookRetryStrategy.RetryTimeFactor,
		Func: func() {
			// Don't try to send on the channel if it's already full
			// This can happen if the timer fires off before the event is consumed
			// by the resolver loop
			select {
			case retryHookChan <- struct{}{}:
			default:
			}
		},
		Clock: u.clock,
	})
	defer func() {
		// Whenever we exit the uniter we want to stop a potentially
		// running timer so it doesn't trigger for nothing.
		retryHookTimer.Reset()
	}()

	restartWatcher := func() error {
		watcherMu.Lock()
		defer watcherMu.Unlock()

		if watcher != nil {
			// watcher added to catacomb, will kill uniter if there's an error.
			worker.Stop(watcher)
		}
		var err error
		watcher, err = remotestate.NewWatcher(
			remotestate.WatcherConfig{
				State:               remotestate.NewAPIState(u.st),
				LeadershipTracker:   u.leadershipTracker,
				UnitTag:             unitTag,
				UpdateStatusChannel: u.updateStatusAt,
				CommandChannel:      u.commandChannel,
				RetryHookChannel:    retryHookChan,
			})
		if err != nil {
			return errors.Trace(err)
		}
		if err := u.catacomb.Add(watcher); err != nil {
			return errors.Trace(err)
		}
		return nil
	}

	onIdle := func() error {
		opState := u.operationExecutor.State()
		if opState.Kind != operation.Continue {
//.........这里部分代码省略.........

func (u *Uniter) loop(unitTag names.UnitTag) (err error) {
	if err := u.init(unitTag); err != nil {
		if err == worker.ErrTerminateAgent {
			return err
		}
		return fmt.Errorf("failed to initialize uniter for %q: %v", unitTag, err)
	}
	logger.Infof("unit %q started", u.unit)

	// Install is a special case, as it must run before there
	// is any remote state, and before the remote state watcher
	// is started.
	var charmURL *corecharm.URL
	opState := u.operationExecutor.State()
	if opState.Kind == operation.Install {
		logger.Infof("resuming charm install")
		op, err := u.operationFactory.NewInstall(opState.CharmURL)
		if err != nil {
			return errors.Trace(err)
		}
		if err := u.operationExecutor.Run(op); err != nil {
			return errors.Trace(err)
		}
		charmURL = opState.CharmURL
	} else {
		curl, err := u.unit.CharmURL()
		if err != nil {
			return errors.Trace(err)
		}
		charmURL = curl
	}

	var (
		watcher   *remotestate.RemoteStateWatcher
		watcherMu sync.Mutex
	)

	restartWatcher := func() error {
		watcherMu.Lock()
		defer watcherMu.Unlock()

		if watcher != nil {
			if err := watcher.Stop(); err != nil {
				return errors.Trace(err)
			}
		}
		var err error
		watcher, err = remotestate.NewWatcher(
			remotestate.WatcherConfig{
				State:               remotestate.NewAPIState(u.st),
				LeadershipTracker:   u.leadershipTracker,
				UnitTag:             unitTag,
				UpdateStatusChannel: u.updateStatusAt,
			})
		if err != nil {
			return errors.Trace(err)
		}
		// Stop the uniter if the watcher fails. The watcher may be
		// stopped cleanly, so only kill the tomb if the error is
		// non-nil.
		go func(w *remotestate.RemoteStateWatcher) {
			if err := w.Wait(); err != nil {
				u.tomb.Kill(err)
			}
		}(watcher)
		return nil
	}

	// watcher may be replaced, so use a closure.
	u.addCleanup(func() error {
		watcherMu.Lock()
		defer watcherMu.Unlock()

		if watcher != nil {
			return watcher.Stop()
		}
		return nil
	})

	onIdle := func() error {
		opState := u.operationExecutor.State()
		if opState.Kind != operation.Continue {
			// We should only set idle status if we're in
			// the "Continue" state, which indicates that
			// there is nothing to do and we're not in an
			// error state.
			return nil
		}
		return setAgentStatus(u, params.StatusIdle, "", nil)
	}

	clearResolved := func() error {
		if err := u.unit.ClearResolved(); err != nil {
			return errors.Trace(err)
		}
		watcher.ClearResolvedMode()
		return nil
	}

	for {
//.........这里部分代码省略.........