// 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
}

// 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
}

// 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)

// 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
}

// 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,
	}
}

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
}

// 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.
// 
// source已经有chan通道，就返回这个chan
// 否则创建一个source的chan，然后启动一个goroutine消费这个chan（对消息进行加工分类，然后将最终的podUpdate消息发送给merger--PodStorage里的updates--chan通道）
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
}

// 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)
    ......

// 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()
}

// 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)
}

// 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
}

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)
}

// 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
		}
	}
}

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)
}

	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
		}
	}

// 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
}

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
}

// 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
}

// 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())
}

// 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)
}