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// PodConfig is a configuration mux that merges many sources of pod configuration into a single
// consistent structure, and then delivers incremental change notifications to listeners
// in order.
type PodConfig struct {
	pods *podStorage
	// 聚合器
	mux  *config.Mux

	// the channel of denormalized changes passed to listeners
	updates chan kubetypes.PodUpdate

	// contains the list of all configured sources
	sourcesLock       sync.Mutex
	sources           sets.String
	checkpointManager checkpointmanager.CheckpointManager
}

// podStorage manages the current pod state at any point in time and ensures updates
// to the channel are delivered in order.  Note that this object is an in-memory source of
// "truth" and on creation contains zero entries.  Once all previously read sources are
// available, then this object should be considered authoritative.
type podStorage struct {
	podLock sync.RWMutex
	// map of source name to pod uid to pod reference
	pods map[string]map[types.UID]*v1.Pod
	mode PodConfigNotificationMode

	// ensures that updates are delivered in strict order
	// on the updates channel
	updateLock sync.Mutex
	updates    chan<- kubetypes.PodUpdate

	// contains the set of all sources that have sent at least one SET
	sourcesSeenLock sync.RWMutex
	sourcesSeen     sets.String

	// the EventRecorder to use
	recorder record.EventRecorder
}

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// PodUpdate defines an operation sent on the channel. You can add or remove single services by
// sending an array of size one and Op == ADD|REMOVE (with REMOVE, only the ID is required).
// For setting the state of the system to a given state for this source configuration, set
// Pods as desired and Op to SET, which will reset the system state to that specified in this
// operation for this source channel. To remove all pods, set Pods to empty object and Op to SET.
//
// Additionally, Pods should never be nil - it should always point to an empty slice. While
// functionally similar, this helps our unit tests properly check that the correct PodUpdates
// are generated.
type PodUpdate struct {
    Pods   []*v1.Pod
    Op     PodOperation
    Source string
}

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	if kubeDeps.PodConfig == nil {
		var err error
		// bootstrapCheckpointPath默认为空
		kubeDeps.PodConfig, err = makePodSourceConfig(kubeCfg, kubeDeps, nodeName, bootstrapCheckpointPath)
		if err != nil {
			return nil, err
		}
	}

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// makePodSourceConfig creates a config.PodConfig from the given
// KubeletConfiguration or returns an error.
func makePodSourceConfig(kubeCfg *kubeletconfiginternal.KubeletConfiguration, kubeDeps *Dependencies, nodeName types.NodeName, bootstrapCheckpointPath string) (*config.PodConfig, error) {
	manifestURLHeader := make(http.Header)
	if len(kubeCfg.StaticPodURLHeader) > 0 {
		for k, v := range kubeCfg.StaticPodURLHeader {
			for i := range v {
				manifestURLHeader.Add(k, v[i])
			}
		}
	}

	// source of all configuration
	cfg := config.NewPodConfig(config.PodConfigNotificationIncremental, kubeDeps.Recorder)

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// NewPodConfig creates an object that can merge many configuration sources into a stream
// of normalized updates to a pod configuration.
func NewPodConfig(mode PodConfigNotificationMode, recorder record.EventRecorder) *PodConfig {
	updates := make(chan kubetypes.PodUpdate, 50)
	storage := newPodStorage(updates, mode, recorder)
	podConfig := &PodConfig{
		pods:    storage,
		mux:     config.NewMux(storage),
		updates: updates,
		sources: sets.String{},
	}
	return podConfig
}

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// TODO: PodConfigNotificationMode could be handled by a listener to the updates channel
// in the future, especially with multiple listeners.
// TODO: allow initialization of the current state of the store with snapshotted version.
func newPodStorage(updates chan<- kubetypes.PodUpdate, mode PodConfigNotificationMode, recorder record.EventRecorder) *podStorage {
	return &podStorage{
		pods:        make(map[string]map[types.UID]*v1.Pod),
		mode:        mode,
		updates:     updates,
		sourcesSeen: sets.String{},
		recorder:    recorder,
	}
}

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type Merger interface {
	// Invoked when a change from a source is received.  May also function as an incremental
	// merger if you wish to consume changes incrementally.  Must be reentrant when more than
	// one source is defined.
	Merge(source string, update interface{}) error
}

// Mux is a class for merging configuration from multiple sources.  Changes are
// pushed via channels and sent to the merge function.
type Mux struct {
	// Invoked when an update is sent to a source.
	merger Merger

	// Sources and their lock.
	sourceLock sync.RWMutex
	// Maps source names to channels
	sources map[string]chan interface{}
}

// NewMux creates a new mux that can merge changes from multiple sources.
func NewMux(merger Merger) *Mux {
	mux := &Mux{
		sources: make(map[string]chan interface{}),
		merger:  merger,
	}
	return mux
}

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func (c *PodConfig) Channel(source string) chan<- interface{} {
	c.sourcesLock.Lock()
	defer c.sourcesLock.Unlock()
	c.sources.Insert(source)
	return c.mux.Channel(source)
}

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// Channel returns a channel where a configuration source
// can send updates of new configurations. Multiple calls with the same
// source will return the same channel. This allows change and state based sources
// to use the same channel. Different source names however will be treated as a
// union.
// 
// If a channel for the source already exists, it returns that channel.
// Otherwise, it creates a new channel for the source and starts a goroutine to consume messages from this channel.
// The goroutine processes messages (categorizing them) and sends the final PodUpdate messages to the merger (which is the PodStorage's updates channel).
func (m *Mux) Channel(source string) chan interface{} {
	if len(source) == 0 {
		panic("Channel given an empty name")
	}
	m.sourceLock.Lock()
	defer m.sourceLock.Unlock()
	channel, exists := m.sources[source]
	if exists {
		return channel
	}
	newChannel := make(chan interface{})
	m.sources[source] = newChannel
	go wait.Until(func() { m.listen(source, newChannel) }, 0, wait.NeverStop)
	return newChannel
}

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func (m *Mux) listen(source string, listenChannel <-chan interface{}) {
	for update := range listenChannel {
        // The merger here is the podStorage
		m.merger.Merge(source, update)
	}
}

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// Merge normalizes a set of incoming changes from different sources into a map of all Pods
// and ensures that redundant changes are filtered out, and then pushes zero or more minimal
// updates onto the update channel.  Ensures that updates are delivered in order.
// 
// 将输入source的PodUpdate的pod列表去重
// 将PodUpdate与s.pods[source]的pod进行比对，加工出各个OP类型PodUpdate，发送到s.updates通道中
// 输入PodUpdate的OP可能与输出PodUpdate的OP不一样
func (s *podStorage) Merge(source string, change interface{}) error {
	s.updateLock.Lock()
	defer s.updateLock.Unlock()

	seenBefore := s.sourcesSeen.Has(source)
	adds, updates, deletes, removes, reconciles, restores := s.merge(source, change)
    ......

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    // define file config source
	// 默认StaticPodPath为空，FileCheckFrequency为20s
	if kubeCfg.StaticPodPath != "" {
		klog.Infof("Adding pod path: %v", kubeCfg.StaticPodPath)
		// Start a goroutine to watch file changes and periodically read files, generating PodUpdate messages (with Op set to SET, including all pods) and sending them to the updates channel
		config.NewSourceFile(kubeCfg.StaticPodPath, nodeName, kubeCfg.FileCheckFrequency.Duration, cfg.Channel(kubetypes.FileSource))
	}

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// NewSourceFile watches a config file for changes.
//
// 启动gorotine watch文件变化和周期性读取文件，生成PodUpdate（op为set，包含所有pod）消息发送给updates通道
func NewSourceFile(path string, nodeName types.NodeName, period time.Duration, updates chan<- interface{}) {
	// "github.com/sigma/go-inotify" requires a path without trailing "/"
	path = strings.TrimRight(path, string(os.PathSeparator))

	config := newSourceFile(path, nodeName, period, updates)
	klog.V(1).Infof("Watching path %q", path)
	config.run()
}

func newSourceFile(path string, nodeName types.NodeName, period time.Duration, updates chan<- interface{}) *sourceFile {
	send := func(objs []interface{}) {
		var pods []*v1.Pod
		for _, o := range objs {
			pods = append(pods, o.(*v1.Pod))
		}
		updates <- kubetypes.PodUpdate{Pods: pods, Op: kubetypes.SET, Source: kubetypes.FileSource}
	}
	store := cache.NewUndeltaStore(send, cache.MetaNamespaceKeyFunc)
	return &sourceFile{
		path:           path,
		nodeName:       nodeName,
		period:         period,
		store:          store,
		fileKeyMapping: map[string]string{},
		updates:        updates,
		watchEvents:    make(chan *watchEvent, eventBufferLen),
	}
}

func (s *sourceFile) run() {
	listTicker := time.NewTicker(s.period)

	go func() {
		// Read path immediately to speed up startup.
		if err := s.listConfig(); err != nil {
			klog.Errorf("Unable to read config path %q: %v", s.path, err)
		}
		for {
			select {
			case <-listTicker.C:
				if err := s.listConfig(); err != nil {
					klog.Errorf("Unable to read config path %q: %v", s.path, err)
				}
			case e := <-s.watchEvents:
				if err := s.consumeWatchEvent(e); err != nil {
					klog.Errorf("Unable to process watch event: %v", err)
				}
			}
		}
	}()

	// 启动goroutine，watch文件变化，生产watchEvents
	s.startWatch()
}

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// extractFromFile parses a file for Pod configuration information.
func (s *sourceFile) extractFromFile(filename string) (pod *v1.Pod, err error) {
	klog.V(3).Infof("Reading config file %q", filename)
	defer func() {
		if err == nil && pod != nil {
			objKey, keyErr := cache.MetaNamespaceKeyFunc(pod)
			if keyErr != nil {
				err = keyErr
				return
			}
			s.fileKeyMapping[filename] = objKey
		}
	}()

	file, err := os.Open(filename)
	if err != nil {
		return pod, err
	}
	defer file.Close()

	data, err := utilio.ReadAtMost(file, maxConfigLength)
	if err != nil {
		return pod, err
	}

	defaultFn := func(pod *api.Pod) error {
		return s.applyDefaults(pod, filename)
	}

	// 解析字节流为pod
	// 生成pod的UID、pod的name、转换空的namespace为default、设置Spec.NodeName、ObjectMeta.SelfLink、添加容忍所有NoExecute taint、设置Status.Phase为pending
	parsed, pod, podErr := tryDecodeSinglePod(data, defaultFn)
	if parsed {
		if podErr != nil {
			return pod, podErr
		}
		return pod, nil
	}

	return pod, fmt.Errorf("%v: couldn't parse as pod(%v), please check config file", filename, podErr)
}

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// 生成pod的UID、pod的name、转换空的namespace为default、设置Spec.NodeName、ObjectMeta.SelfLink、添加容忍所有NoExecute taint、设置Status.Phase为pending
func applyDefaults(pod *api.Pod, source string, isFile bool, nodeName types.NodeName) error {
	if len(pod.UID) == 0 {
		hasher := md5.New()
		if isFile {
			fmt.Fprintf(hasher, "host:%s", nodeName)
			fmt.Fprintf(hasher, "file:%s", source)
		} else {
			fmt.Fprintf(hasher, "url:%s", source)
		}
		hash.DeepHashObject(hasher, pod)
		pod.UID = types.UID(hex.EncodeToString(hasher.Sum(nil)[0:]))
		klog.V(5).Infof("Generated UID %q pod %q from %s", pod.UID, pod.Name, source)
	}

	pod.Name = generatePodName(pod.Name, nodeName)
	klog.V(5).Infof("Generated Name %q for UID %q from URL %s", pod.Name, pod.UID, source)

	if pod.Namespace == "" {
		pod.Namespace = metav1.NamespaceDefault
	}
	klog.V(5).Infof("Using namespace %q for pod %q from %s", pod.Namespace, pod.Name, source)

	// Set the Host field to indicate this pod is scheduled on the current node.
	pod.Spec.NodeName = string(nodeName)

	pod.ObjectMeta.SelfLink = getSelfLink(pod.Name, pod.Namespace)

	if pod.Annotations == nil {
		pod.Annotations = make(map[string]string)
	}
	// The generated UID is the hash of the file.
	pod.Annotations[kubetypes.ConfigHashAnnotationKey] = string(pod.UID)

	if isFile {
		// Applying the default Taint tolerations to static pods,
		// so they are not evicted when there are node problems.
		// 容忍所有NoExecute taint
		helper.AddOrUpdateTolerationInPod(pod, &api.Toleration{
			Operator: "Exists",
			Effect:   api.TaintEffectNoExecute,
		})
	}

	// Set the default status to pending.
	pod.Status.Phase = api.PodPending
	return nil
}

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func (s *sourceFile) startWatch() {
	backOff := flowcontrol.NewBackOff(retryPeriod, maxRetryPeriod)
	backOffID := "watch"

	// 如果func()执行完成，等待一秒后重新执行
	// watch文件变化发生错误的时候，等待1秒，查询是否在回退周期内，不在回退周期内，重新执行watch
	go wait.Forever(func() {
		// 在回退周期中
		if backOff.IsInBackOffSinceUpdate(backOffID, time.Now()) {
			return
		}

		if err := s.doWatch(); err != nil {
			klog.Errorf("Unable to read config path %q: %v", s.path, err)
			// 发生不是文件不存在的错误，进行回退
			if _, retryable := err.(*retryableError); !retryable {
				backOff.Next(backOffID, time.Now())
			}
		}
	}, retryPeriod)
}

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	// define url config source
	// 默认StaticPodURL为空，HTTPCheckFrequency默认为20s
	if kubeCfg.StaticPodURL != "" {
		klog.Infof("Adding pod url %q with HTTP header %v", kubeCfg.StaticPodURL, manifestURLHeader)
		// 启动goroutine 周期请求url获取pod或podlist，生成PodUpdate（op为set，包含所有pod）消息发送给updates通道
		config.NewSourceURL(kubeCfg.StaticPodURL, manifestURLHeader, nodeName, kubeCfg.HTTPCheckFrequency.Duration, cfg.Channel(kubetypes.HTTPSource))
	}

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// NewSourceURL specifies the URL where to read the Pod configuration from, then watches it for changes.
//
// 启动goroutine 周期请求url获取pod或podlist，生成PodUpdate（op为set，包含所有pod）消息发送给updates通道
func NewSourceURL(url string, header http.Header, nodeName types.NodeName, period time.Duration, updates chan<- interface{}) {
	config := &sourceURL{
		url:      url,
		header:   header,
		nodeName: nodeName,
		updates:  updates,
		data:     nil,
		// Timing out requests leads to retries. This client is only used to
		// read the manifest URL passed to kubelet.
		client: &http.Client{Timeout: 10 * time.Second},
	}
	klog.V(1).Infof("Watching URL %s", url)
	go wait.Until(config.run, period, wait.NeverStop)
}

func (s *sourceURL) run() {
	if err := s.extractFromURL(); err != nil {
		// Don't log this multiple times per minute. The first few entries should be
		// enough to get the point across.
		if s.failureLogs < 3 {
			klog.Warningf("Failed to read pods from URL: %v", err)
		} else if s.failureLogs == 3 {
			klog.Warningf("Failed to read pods from URL. Dropping verbosity of this message to V(4): %v", err)
		} else {
			klog.V(4).Infof("Failed to read pods from URL: %v", err)
		}
		s.failureLogs++
	} else {
		if s.failureLogs > 0 {
			klog.Info("Successfully read pods from URL.")
			s.failureLogs = 0
		}
	}
}

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func (s *sourceURL) extractFromURL() error {
	req, err := http.NewRequest("GET", s.url, nil)
	if err != nil {
		return err
	}
	req.Header = s.header
	resp, err := s.client.Do(req)
	if err != nil {
		return err
	}
	defer resp.Body.Close()
	data, err := utilio.ReadAtMost(resp.Body, maxConfigLength)
	if err != nil {
		return err
	}
	if resp.StatusCode != http.StatusOK {
		return fmt.Errorf("%v: %v", s.url, resp.Status)
	}
	if len(data) == 0 {
		// Emit an update with an empty PodList to allow HTTPSource to be marked as seen
		s.updates <- kubetypes.PodUpdate{Pods: []*v1.Pod{}, Op: kubetypes.SET, Source: kubetypes.HTTPSource}
		return fmt.Errorf("zero-length data received from %v", s.url)
	}
	// Short circuit if the data has not changed since the last time it was read.
	if bytes.Equal(data, s.data) {
		return nil
	}
	s.data = data

	// First try as it is a single pod.
	parsed, pod, singlePodErr := tryDecodeSinglePod(data, s.applyDefaults)
	if parsed {
		if singlePodErr != nil {
			// It parsed but could not be used.
			return singlePodErr
		}
		s.updates <- kubetypes.PodUpdate{Pods: []*v1.Pod{pod}, Op: kubetypes.SET, Source: kubetypes.HTTPSource}
		return nil
	}

	// That didn't work, so try a list of pods.
	parsed, podList, multiPodErr := tryDecodePodList(data, s.applyDefaults)
	if parsed {
		if multiPodErr != nil {
			// It parsed but could not be used.
			return multiPodErr
		}
		pods := make([]*v1.Pod, 0)
		for i := range podList.Items {
			pods = append(pods, &podList.Items[i])
		}
		s.updates <- kubetypes.PodUpdate{Pods: pods, Op: kubetypes.SET, Source: kubetypes.HTTPSource}
		return nil
	}

	return fmt.Errorf("%v: received '%v', but couldn't parse as "+
		"single (%v) or multiple pods (%v)",
		s.url, string(data), singlePodErr, multiPodErr)
}

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	var updatechannel chan<- interface{}
	// 默认bootstrapCheckpointPath为空
	if bootstrapCheckpointPath != "" {
		klog.Infof("Adding checkpoint path: %v", bootstrapCheckpointPath)
		updatechannel = cfg.Channel(kubetypes.ApiserverSource)
		// 从目录中读取所有checkpoint文件获取所有pod，然后发送PodUpdate（op为restore）到updatechannel
		err := cfg.Restore(bootstrapCheckpointPath, updatechannel)
		if err != nil {
			return nil, err
		}
	}

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// Restore restores pods from the checkpoint path, *once*
func (c *PodConfig) Restore(path string, updates chan<- interface{}) error {
	if c.checkpointManager != nil {
		return nil
	}
	var err error
	c.checkpointManager, err = checkpointmanager.NewCheckpointManager(path)
	if err != nil {
		return err
	}
	pods, err := checkpoint.LoadPods(c.checkpointManager)
	if err != nil {
		return err
	}
	updates <- kubetypes.PodUpdate{Pods: pods, Op: kubetypes.RESTORE, Source: kubetypes.ApiserverSource}
	return nil
}

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type Data struct {
	Pod      *v1.Pod
	Checksum checksum.Checksum
}

// NewPodCheckpoint returns new pod checkpoint
func NewPodCheckpoint(pod *v1.Pod) PodCheckpoint {
	return &Data{Pod: pod}
}

// LoadPods Loads All Checkpoints from disk
func LoadPods(cpm checkpointmanager.CheckpointManager) ([]*v1.Pod, error) {
	pods := make([]*v1.Pod, 0)

	// 获得目录下的所有文件列表
	checkpointKeys, err := cpm.ListCheckpoints()
	if err != nil {
		klog.Errorf("Failed to list checkpoints: %v", err)
	}

	for _, key := range checkpointKeys {
		checkpoint := NewPodCheckpoint(nil)
		// 将文件的内容转化成checkpoint--包含pod和checksum
		err := cpm.GetCheckpoint(key, checkpoint)
		if err != nil {
			klog.Errorf("Failed to retrieve checkpoint for pod %q: %v", key, err)
			continue
		}
		pods = append(pods, checkpoint.GetPod())
	}
	return pods, nil
}

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// GetCheckpoint retrieves checkpoint from CheckpointStore.
func (manager *impl) GetCheckpoint(checkpointKey string, checkpoint Checkpoint) error {
	manager.mutex.Lock()
	defer manager.mutex.Unlock()
    //读取文件
	blob, err := manager.store.Read(checkpointKey)
	if err != nil {
		if err == utilstore.ErrKeyNotFound {
			return errors.ErrCheckpointNotFound
		}
		return err
	}
	err = checkpoint.UnmarshalCheckpoint(blob)
	if err == nil {
		err = checkpoint.VerifyChecksum()
	}
	return err
}

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// UnmarshalCheckpoint returns unmarshalled data
func (cp *Data) UnmarshalCheckpoint(blob []byte) error {
	return json.Unmarshal(blob, cp)
}

// VerifyChecksum verifies that passed checksum is same as calculated checksum
func (cp *Data) VerifyChecksum() error {
	return cp.Checksum.Verify(*cp.Pod)
}

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// Checksum is the data to be stored as checkpoint
type Checksum uint64

// Verify verifies that passed checksum is same as calculated checksum
func (cs Checksum) Verify(data interface{}) error {
	if cs != New(data) {
		return errors.ErrCorruptCheckpoint
	}
	return nil
}

// New returns the Checksum of checkpoint data
func New(data interface{}) Checksum {
	return Checksum(getChecksum(data))
}

// Get returns calculated checksum of checkpoint data
func getChecksum(data interface{}) uint64 {
	hash := fnv.New32a()
	hashutil.DeepHashObject(hash, data)
	return uint64(hash.Sum32())
}

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    if kubeDeps.KubeClient != nil {
		klog.Infof("Watching apiserver")
		if updatechannel == nil {
			updatechannel = cfg.Channel(kubetypes.ApiserverSource)
		}
		config.NewSourceApiserver(kubeDeps.KubeClient, nodeName, updatechannel)
	}

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// NewSourceApiserver creates a config source that watches and pulls from the apiserver.
func NewSourceApiserver(c clientset.Interface, nodeName types.NodeName, updates chan<- interface{}) {
	lw := cache.NewListWatchFromClient(c.CoreV1().RESTClient(), "pods", metav1.NamespaceAll, fields.OneTermEqualSelector(api.PodHostField, string(nodeName)))
	newSourceApiserverFromLW(lw, updates)
}

// newSourceApiserverFromLW holds creates a config source that watches and pulls from the apiserver.
func newSourceApiserverFromLW(lw cache.ListerWatcher, updates chan<- interface{}) {
	send := func(objs []interface{}) {
		var pods []*v1.Pod
		for _, o := range objs {
			pods = append(pods, o.(*v1.Pod))
		}
		updates <- kubetypes.PodUpdate{Pods: pods, Op: kubetypes.SET, Source: kubetypes.ApiserverSource}
	}
	r := cache.NewReflector(lw, &v1.Pod{}, cache.NewUndeltaStore(send, cache.MetaNamespaceKeyFunc), 0)
	go r.Run(wait.NeverStop)
}