update

byteview.go

@@ -31,6 +31,7 @@ import (
 // a pointer (like a time.Time).
 type ByteView struct {
  // If b is non-nil, b is used, else s is used.
+ // 当b是nil 的时候，s作为存储内容的容器
  b []byte
  s string
 }

http.go

@@ -40,17 +40,22 @@ type HTTPPool struct {
  // Context optionally specifies a context for the server to use when it
  // receives a request.
  // If nil, the server uses the request's context
+ // 其中 Context可根据情况定制，主要用于服务端，将接收到的http请求转换成指定的context类型，便于进一步处理
  Context func(*http.Request) context.Context
 
  // Transport optionally specifies an http.RoundTripper for the client
  // to use when it makes a request.
  // If nil, the client uses http.DefaultTransport.
+ // Transport可根据情况定制，主要用于客户端，将一个向对等节点发起的请求context，转换成指定的Http访问方式，其中 RoundTripper为实现了
+ // RoundTrip(*Request) (*Response, error)的接口，故而，HTTPPool可以实现访问方式的灵活定制
  Transport func(context.Context) http.RoundTripper
 
  // this peer's base URL, e.g. "https://example.net:8000"
+ // 该节点本身的URL，为监听服务的地址
  self string
 
  // opts specifies the options.
+ // HTTP池的默认选项
  opts HTTPPoolOptions
 
  mu sync.Mutex // guards peers and httpGetters
@@ -62,14 +67,17 @@ type HTTPPool struct {
 type HTTPPoolOptions struct {
  // BasePath specifies the HTTP path that will serve groupcache requests.
  // If blank, it defaults to "/_groupcache/".
+ // http服务地址前缀，默认为 "/_groupcache/".
  BasePath string
 
  // Replicas specifies the number of key replicas on the consistent hash.
  // If blank, it defaults to 50.
+ // 分布式一致性hash中虚拟节点数量，默认 50.
  Replicas int
 
  // HashFn specifies the hash function of the consistent hash.
  // If blank, it defaults to crc32.ChecksumIEEE.
+ // 分布式一致性hash的hash算法，默认 crc32.ChecksumIEEE.
  HashFn consistenthash.Hash
 }
 
@@ -139,11 +147,14 @@ func (p *HTTPPool) PickPeer(key string) (ProtoGetter, bool) {
  return nil, false
 }
 
+// ServeHTTP 实现了http服务的具体方法
 func (p *HTTPPool) ServeHTTP(w http.ResponseWriter, r *http.Request) {
  // Parse request.
+ // 判断URL前缀是否合法
  if !strings.HasPrefix(r.URL.Path, p.opts.BasePath) {
  panic("HTTPPool serving unexpected path: " + r.URL.Path)
  }
+ // 分割URL，并从中提取group和key值，示例请求URL为：https://example.net:8000/_groupcache/groupname/key
  parts := strings.SplitN(r.URL.Path[len(p.opts.BasePath):], "/", 2)
  if len(parts) != 2 {
  http.Error(w, "bad request", http.StatusBadRequest)
@@ -152,6 +163,7 @@ func (p *HTTPPool) ServeHTTP(w http.ResponseWriter, r *http.Request) {
  groupName := parts[0]
  key := parts[1]
 
+ // 根据url中提取的groupname 获取group
  // Fetch the value for this group/key.
  group := GetGroup(groupName)
  if group == nil {
@@ -160,26 +172,31 @@ func (p *HTTPPool) ServeHTTP(w http.ResponseWriter, r *http.Request) {
  }
  var ctx context.Context
  if p.Context != nil {
+ // 如Context不为空，说明需要使用定制的context
  ctx = p.Context(r)
  } else {
  ctx = r.Context()
  }
 
  group.Stats.ServerRequests.Add(1)
  var value []byte
+ // 获取指定key对应的缓存
  err := group.Get(ctx, key, AllocatingByteSliceSink(&value))
  if err != nil {
  http.Error(w, err.Error(), http.StatusInternalServerError)
  return
  }
 
  // Write the value to the response body as a proto message.
+ // 序列化响应内容
  body, err := proto.Marshal(&pb.GetResponse{Value: value})
  if err != nil {
  http.Error(w, err.Error(), http.StatusInternalServerError)
  return
  }
+ // 设置http头
  w.Header().Set("Content-Type", "application/x-protobuf")
+ // 设置http body
  w.Write(body)
 }
 
@@ -208,6 +225,7 @@ func (h *httpGetter) Get(ctx context.Context, in *pb.GetRequest, out *pb.GetResp
  if h.transport != nil {
  tr = h.transport(ctx)
  }
+ // 执行请求
  res, err := tr.RoundTrip(req)
  if err != nil {
  return err

sinks.go

@@ -26,6 +26,7 @@ import (
 //
 // Implementation of Getter must call exactly one of the Set methods
 // on success.
+// stringSink、byteViewSink、protoSink、allocBytesSink、truncBytesSink，顾名思义，不同的类型代表了其内部的存储方式的不同
 type Sink interface {
  // SetString sets the value to s.
  SetString(s string) error