源码阅读之storm操作zookeeper-cluster.clj

storm操作zookeeper的主要函数都定义在命名空间backtype.storm.cluster中（即cluster.clj文件中）。 backtype.storm.cluster定义了两个重要protocol：ClusterState和StormClusterState。

clojure中的protocol可以看成java中的接口，封装了一组方法。ClusterState协议中封装了一组与zookeeper进行交互的基础函数，如获取子节点函数，获取子节点数据函数等，ClusterState协议定义如下：

ClusterState协议

(defprotocol ClusterState
  (set-ephemeral-node [this path data])
  (delete-node [this path])
  (create-sequential [this path data])
  ;; if node does not exist, create persistent with this data
  (set-data [this path data])
  (get-data [this path watch?])
  (get-version [this path watch?])
  (get-data-with-version [this path watch?])
  (get-children [this path watch?])
  (mkdirs [this path])
  (close [this])
  (register [this callback])
  (unregister [this id]))

StormClusterState协议封装了一组storm与zookeeper进行交互的函数，可以将StormClusterState协议中的函数看成ClusterState协议中函数的"组合"。StormClusterState协议定义如下：

StormClusterState协议

(defprotocol StormClusterState
 (assignments [this callback])
 (assignment-info [this storm-id callback])
 (assignment-info-with-version [this storm-id callback])
 (assignment-version [this storm-id callback])
 (active-storms [this])
 (storm-base [this storm-id callback])
 (get-worker-heartbeat [this storm-id node port])
 (executor-beats [this storm-id executor->node+port])
 (supervisors [this callback])
 (supervisor-info [this supervisor-id]) ;; returns nil if doesn't exist
 (setup-heartbeats! [this storm-id])
 (teardown-heartbeats! [this storm-id])
 (teardown-topology-errors! [this storm-id])
 (heartbeat-storms [this])
 (error-topologies [this])
 (worker-heartbeat! [this storm-id node port info])
 (remove-worker-heartbeat! [this storm-id node port])
 (supervisor-heartbeat! [this supervisor-id info])
 (activate-storm! [this storm-id storm-base])
 (update-storm! [this storm-id new-elems])
 (remove-storm-base! [this storm-id])
 (set-assignment! [this storm-id info])
 (remove-storm! [this storm-id])
 (report-error [this storm-id task-id node port error])
 (errors [this storm-id task-id])
 (disconnect [this]))

命名空间backtype.storm.cluster除了定义ClusterState和StormClusterState这两个重要协议外，还定义了两个重要函数：mk-distributed-cluster-state和mk-storm-cluster-state。

mk-distributed-cluster-state函数如下：

该函数返回一个实现了ClusterState协议的对象，通过这个对象就可以与zookeeper进行交互了。

mk-distributed-cluster-state函数

(defn mk-distributed-cluster-state
;; conf绑定了storm.yaml中的配置信息，是一个map对象
[conf]
;; zk绑定一个zk client，Storm使用CuratorFramework与Zookeeper进行交互
(let [zk (zk/mk-client conf (conf STORM-ZOOKEEPER-SERVERS) (conf STORM-ZOOKEEPER-PORT)            :auth-conf conf)]
  ;; 创建storm集群在zookeeper上的根目录，默认值为/storm
  (zk/mkdirs zk (conf STORM-ZOOKEEPER-ROOT))
  (.close zk))
;; callbacks绑定回调函数集合，是一个map对象
(let [callbacks (atom {})
  ;; active标示zookeeper集群状态
  active (atom true)
  ;; zk重新绑定新的zk client，该zk client设置了watcher，这样当zookeeper集群的状态发生变化时，zk server会给zk client发送相应的event，zk client设置的watcher会调用callbacks中相应回调函数来处理event
  ;; 启动nimbus时，callbacks是一个空集合，所以nimbus端收到event后不会调用任何回调函数；但是启动supervisor时，callbacks中注册了回调函数，所以当supervisor收到zk server发送的event后，会调用相应的回调函数
  ;; mk-client函数定义在zookeeper.clj文件中，请参见其定义部分
  zk (zk/mk-client conf
           (conf STORM-ZOOKEEPER-SERVERS)
           (conf STORM-ZOOKEEPER-PORT)
           :auth-conf conf
           :root (conf STORM-ZOOKEEPER-ROOT)
           ;; :watcher绑定一个函数，指定zk client的默认watcher函数，state标示当前zk client的状态；type标示事件类型；path标示zookeeper上产生该事件的znode
           ;; 该watcher函数主要功能就是执行callbacks集合中的函数，callbacks集合中的函数是在mk-storm-cluster-state函数中通过调用ClusterState的register函数添加的
           :watcher (fn [state type path]
                (when @active
                 (when-not (= :connected state)
                  (log-warn "Received event " state ":" type ":" path " with disconnected Zookeeper."))
                 (when-not (= :none type)
                  (doseq [callback (vals @callbacks)]
                   (callback type path))))))]
;; reify相当于java中的implements，这里表示实现一个协议
(reify
 ClusterState
 ;; register函数用于将回调函数加入callbacks中，key是一个32位的标识
 (register
  [this callback]
  (let [id (uuid)]
   (swap! callbacks assoc id callback)
   id))
 ;; unregister函数用于将指定key的回调函数从callbacks中删除
 (unregister
  [this id]
  (swap! callbacks dissoc id))
 ;; 在zookeeper上添加一个临时节点
 (set-ephemeral-node
  [this path data]
  (zk/mkdirs zk (parent-path path))
  (if (zk/exists zk path false)
   (try-cause
    (zk/set-data zk path data) ; should verify that it's ephemeral
    (catch KeeperException$NoNodeException e
     (log-warn-error e "Ephemeral node disappeared between checking for existing and setting data")
     (zk/create-node zk path data :ephemeral)
     ))
   (zk/create-node zk path data :ephemeral)))
 ;; 在zookeeper上添加一个顺序节点
 (create-sequential
  [this path data]
  (zk/create-node zk path data :sequential))
 ;; 修改某个节点数据
 (set-data
  [this path data]
  ;; note: this does not turn off any existing watches
  (if (zk/exists zk path false)
   (zk/set-data zk path data)
   (do
    (zk/mkdirs zk (parent-path path))
    (zk/create-node zk path data :persistent))))
 ;; 删除指定节点
 (delete-node
  [this path]
  (zk/delete-recursive zk path))
 ;; 获取指定节点数据。path标示节点路径；watch?是一个布尔类型值，表示是否需要对该节点进行"观察"，如果watch?=true，当调用set-data函数修改该节点数据后，
 ;; 会给zk client发送一个事件，zk client接收事件后，会调用创建zk client时指定的默认watcher函数（即:watcher绑定的函数）
 (get-data
  [this path watch?]
  (zk/get-data zk path watch?))
 ;; 与get-data函数的区别就是获取指定节点数据的同时，获取节点数据的version，version表示节点数据修改的次数
 (get-data-with-version
  [this path watch?]
  (zk/get-data-with-version zk path watch?))
 ;; 获取指定节点的version，watch?的含义与get-data函数中的watch?相同
 (get-version
  [this path watch?]
  (zk/get-version zk path watch?))
 ;; 获取指定节点的子节点列表，watch?的含义与get-data函数中的watch?相同
 (get-children
  [this path watch?]
  (zk/get-children zk path watch?))
 ;; 在zookeeper上创建一个节点
 (mkdirs
  [this path]
  (zk/mkdirs zk path))
 ;; 关闭zk client
 (close
  [this]
  (reset! active false)
  (.close zk)))))

mk-storm-cluster-state函数定义如下：

mk-storm-cluster-state函数非常重要，该函数返回一个实现了StormClusterState协议的实例，通过该实例storm就可以更加方便与zookeeper进行交互。

在启动nimbus和supervisor的函数中均调用了mk-storm-cluster-state函数。关于nimbus和supervisor的启动将在之后的文章中介绍。

mk-storm-cluster-state函数

(defn mk-storm-cluster-state
 [cluster-state-spec]
 ;; satisfies?谓词相当于java中的instanceof，判断cluster-state-spec是不是ClusterState实例
 (let [[solo? cluster-state] (if (satisfies? ClusterState cluster-state-spec)
              [false cluster-state-spec]
              [true (mk-distributed-cluster-state cluster-state-spec)])
  ;; 绑定topology id->回调函数的map，当/assignments/{topology id}数据发生变化时，zk client执行assignment-info-callback中topology id所对应的回调函数
  assignment-info-callback (atom {})
  ;; assignment-info-with-version-callback与assignment-info-callback类似
  assignment-info-with-version-callback (atom {})
  ;; assignment-version-callback与assignments-callback类似
  assignment-version-callback (atom {})
  ;; 当/supervisors标示的znode的子节点发生变化时，zk client执行supervisors-callback指向的函数
  supervisors-callback (atom nil)
  ;; 当/assignments标示的znode的子节点发生变化时，zk client执行assignments-callback指向的函数
  assignments-callback (atom nil)
  ;; 当/storms/{topology id}标示的znode的数据发生变化时，zk client执行storm-base-callback中topology id所对应的回调函数
  storm-base-callback (atom {})
  ;; register函数将"回调函数(fn ...)"添加到cluster-state的callbacks集合中，并返回标示该回调函数的uuid
  state-id (register
        cluster-state
        ;; 定义"回调函数"，type标示事件类型，path标示znode
        (fn [type path]
         ;; subtree绑定路径前缀如"assignments"、"storms"、"supervisors"等，args存放topology id
         (let [[subtree & args] (tokenize-path path)]
          ;; condp相当于java中的switch
          (condp = subtree
           ;; 当subtree="assignments"时，如果args为空，说明是/assignments的子节点发生变化，执行assignments-callback指向的回调函数，否则
     ;; 说明/assignments/{topology id}标示的节点数据发生变化，执行assignment-info-callback指向的回调函数
           ASSIGNMENTS-ROOT (if (empty? args)
                    (issue-callback! assignments-callback)
                    (issue-map-callback! assignment-info-callback (first args)))
           ;; 当subtree="supervisors"时，说明是/supervisors的子节点发生变化，执行supervisors-callback指向的回调函数
           SUPERVISORS-ROOT (issue-callback! supervisors-callback)
           ;; 当subtree="storms"时，说明是/storms/{topology id}标示的节点数据发生变化，执行storm-base-callback指向的回调函数
           STORMS-ROOT (issue-map-callback! storm-base-callback (first args))
           ;; this should never happen
           (exit-process! 30 "Unknown callback for subtree " subtree args)))))]
;; 在zookeeper上创建storm运行topology所必需的znode
(doseq [p [ASSIGNMENTS-SUBTREE STORMS-SUBTREE SUPERVISORS-SUBTREE WORKERBEATS-SUBTREE ERRORS-SUBTREE]]
 (mkdirs cluster-state p))
;; 返回一个实现StormClusterState协议的实例
(reify
 StormClusterState
 ;; 获取/assignments的子节点列表，如果callback不为空，将其赋值给assignments-callback，并对/assignments添加"节点观察"
 (assignments
  [this callback]
  (when callback
   (reset! assignments-callback callback))
  (get-children cluster-state ASSIGNMENTS-SUBTREE (not-nil? callback)))
 ;; 获取/assignments/{storm-id}节点数据，即storm-id的分配信息，如果callback不为空，将其添加到assignment-info-callback中，并对/assignments/{storm-id}添加"数据观察"
 (assignment-info
  [this storm-id callback]
  (when callback
   (swap! assignment-info-callback assoc storm-id callback))
  (maybe-deserialize (get-data cluster-state (assignment-path storm-id) (not-nil? callback))))
 ;; 获取/assignments/{storm-id}节点数据包括version信息，如果callback不为空，将其添加到assignment-info-with-version-callback中，并对/assignments/{storm-id}添加"数据观察"
 (assignment-info-with-version
  [this storm-id callback]
  (when callback
   (swap! assignment-info-with-version-callback assoc storm-id callback))
  (let [{data :data version :version}
     (get-data-with-version cluster-state (assignment-path storm-id) (not-nil? callback))]
  {:data (maybe-deserialize data)
   :version version}))
 ;; 获取/assignments/{storm-id}节点数据的version信息，如果callback不为空，将其添加到assignment-version-callback中，并对/assignments/{storm-id}添加"数据观察"
 (assignment-version
  [this storm-id callback]
  (when callback
   (swap! assignment-version-callback assoc storm-id callback))
  (get-version cluster-state (assignment-path storm-id) (not-nil? callback)))
 ;; 获取storm集群中正在运行的topology id即/storms的子节点列表
 (active-storms
  [this]
  (get-children cluster-state STORMS-SUBTREE false))
 ;; 获取storm集群中所有有心跳的topology id即/workerbeats的子节点列表
 (heartbeat-storms
  [this]
  (get-children cluster-state WORKERBEATS-SUBTREE false))
 ;; 获取所有有错误的topology id即/errors的子节点列表
 (error-topologies
  [this]
  (get-children cluster-state ERRORS-SUBTREE false))
 ;; 获取指定storm-id进程的心跳信息，即/workerbeats/{storm-id}/{node-port}节点数据
 (get-worker-heartbeat
  [this storm-id node port]
  (-> cluster-state
    (get-data (workerbeat-path storm-id node port) false)
    maybe-deserialize))
 ;; 获取指定进程中所有线程的心跳信息
 (executor-beats
  [this storm-id executor->node+port]
  ;; need to take executor->node+port in explicitly so that we don't run into a situation where a
  ;; long dead worker with a skewed clock overrides all the timestamps. By only checking heartbeats
  ;; with an assigned node+port, and only reading executors from that heartbeat that are actually assigned,
  ;; we avoid situations like that
  (let [node+port->executors (reverse-map executor->node+port)
     all-heartbeats (for [[[node port] executors] node+port->executors]
              (->> (get-worker-heartbeat this storm-id node port)
                (convert-executor-beats executors)
                ))]
   (apply merge all-heartbeats)))
 ;; 获取/supervisors的子节点列表，如果callback不为空，将其赋值给supervisors-callback，并对/supervisors添加"节点观察"
 (supervisors
  [this callback]
  (when callback
   (reset! supervisors-callback callback))
  (get-children cluster-state SUPERVISORS-SUBTREE (not-nil? callback)))
 ;; 获取/supervisors/{supervisor-id}节点数据，即supervisor的心跳信息
 (supervisor-info
  [this supervisor-id]
  (maybe-deserialize (get-data cluster-state (supervisor-path supervisor-id) false)))
 ;; 设置进程心跳信息
 (worker-heartbeat!
  [this storm-id node port info]
  (set-data cluster-state (workerbeat-path storm-id node port) (Utils/serialize info)))
 ;; 删除进程心跳信息
 (remove-worker-heartbeat!
  [this storm-id node port]
  (delete-node cluster-state (workerbeat-path storm-id node port)))
 ;; 创建指定storm-id的topology的用于存放心跳信息的节点
 (setup-heartbeats!
  [this storm-id]
  (mkdirs cluster-state (workerbeat-storm-root storm-id)))
 ;; 删除指定storm-id的topology的心跳信息节点
 (teardown-heartbeats!
  [this storm-id]
  (try-cause
   (delete-node cluster-state (workerbeat-storm-root storm-id))
   (catch KeeperException e
    (log-warn-error e "Could not teardown heartbeats for " storm-id))))
 ;; 删除指定storm-id的topology的错误信息节点
 (teardown-topology-errors!
  [this storm-id]
  (try-cause
   (delete-node cluster-state (error-storm-root storm-id))
   (catch KeeperException e
    (log-warn-error e "Could not teardown errors for " storm-id))))
 ;; 创建临时节点存放supervisor的心跳信息
 (supervisor-heartbeat!
  [this supervisor-id info]
  (set-ephemeral-node cluster-state (supervisor-path supervisor-id) (Utils/serialize info)))
 ;; 创建/storms/{storm-id}节点
 (activate-storm!
  [this storm-id storm-base]
  (set-data cluster-state (storm-path storm-id) (Utils/serialize storm-base)))
 ;; 更新topology对应的StormBase对象，即更新/storm/{storm-id}节点
 (update-storm!
  [this storm-id new-elems]
  ;; base绑定storm-id在zookeeper上的StormBase对象
  (let [base (storm-base this storm-id nil)
     ;; executors绑定component名称->组件并行度的map
     executors (:component->executors base)
     ;; new-elems绑定合并后的组件并行度map，update函数将组件新并行度map合并到旧map中
     new-elems (update new-elems :component->executors (partial merge executors))]
   ;; 更新StormBase对象中的组件并行度map，并写入zookeeper的/storms/{storm-id}节点
   (set-data cluster-state (storm-path storm-id)
        (-> base
          (merge new-elems)
          Utils/serialize))))
 ;; 获取storm-id的StormBase对象，即读取/storms/{storm-id}节点数据，如果callback不为空，将其赋值给storm-base-callback，并为/storms/{storm-id}节点添加"数据观察"
 (storm-base
  [this storm-id callback]
  (when callback
   (swap! storm-base-callback assoc storm-id callback))
  (maybe-deserialize (get-data cluster-state (storm-path storm-id) (not-nil? callback))))
 ;; 删除storm-id的StormBase对象，即删除/storms/{storm-id}节点
 (remove-storm-base!
  [this storm-id]
  (delete-node cluster-state (storm-path storm-id)))
 ;; 更新storm-id的分配信息，即更新/assignments/{storm-id}节点数据
 (set-assignment!
  [this storm-id info]
  (set-data cluster-state (assignment-path storm-id) (Utils/serialize info)))
 ;; 删除storm-id的分配信息，同时删除其StormBase信息，即删除/assignments/{storm-id}节点和/storms/{storm-id}节点
 (remove-storm!
  [this storm-id]
  (delete-node cluster-state (assignment-path storm-id))
  (remove-storm-base! this storm-id))
 ;; 将组件异常信息写入zookeeper
 (report-error
  [this storm-id component-id node port error]
  ;; path绑定"/errors/{storm-id}/{component-id}"
  (let [path (error-path storm-id component-id)
     ;; data绑定异常信息，包括异常时间、异常堆栈信息、主机和端口
     data {:time-secs (current-time-secs) :error (stringify-error error) :host node :port port}
     ;; 创建/errors/{storm-id}/{component-id}节点
     _ (mkdirs cluster-state path)
     ;; 创建/errors/{storm-id}/{component-id}的子顺序节点，并写入异常信息
     _ (create-sequential cluster-state (str path "/e") (Utils/serialize data))
     ;; to-kill绑定除去顺序节点编号最大的前10个节点的剩余节点的集合
     to-kill (->> (get-children cluster-state path false)
            (sort-by parse-error-path)
            reverse
            (drop 10))]
   ;; 删除to-kill中包含的节点
   (doseq [k to-kill]
    (delete-node cluster-state (str path "/" k)))))
 ;; 得到给定的storm-id component-id下的异常信息
 (errors
  [this storm-id component-id]
  (let [path (error-path storm-id component-id)
     _ (mkdirs cluster-state path)
     children (get-children cluster-state path false)
     errors (dofor [c children]
            (let [data (-> (get-data cluster-state (str path "/" c) false)
                    maybe-deserialize)]
             (when data
              (struct TaskError (:error data) (:time-secs data) (:host data) (:port data))
              )))
     ]
   (->> (filter not-nil? errors)
      (sort-by (comp - :time-secs)))))
 ;; 关闭连接，在关闭连接前，将回调函数从cluster-state的callbacks中删除
 (disconnect
  [this]
  (unregister cluster-state state-id)
  (when solo?
   (close cluster-state))))))

zookeeper.clj中mk-client函数

mk-client函数创建一个CuratorFramework实例，为该实例注册了CuratorListener，当一个后台操作完成或者指定的watch被触发时将会执行CuratorListener中的eventReceived()。eventReceived中调用的wacher函数就是mk-distributed-cluster-state中:watcher绑定的函数。

(defnk mk-client
 [conf servers port
  :root ""
  :watcher default-watcher
  :auth-conf nil]
 (let [fk (Utils/newCurator conf servers port root (when auth-conf (ZookeeperAuthInfo. auth-conf)))]
  (.. fk
    (getCuratorListenable)
    (addListener
     (reify CuratorListener
      (^void eventReceived [this ^CuratorFramework _fk ^CuratorEvent e]
        (when (= (.getType e) CuratorEventType/WATCHED)
         (let [^WatchedEvent event (.getWatchedEvent e)]
          (watcher (zk-keeper-states (.getState event))
              (zk-event-types (.getType event))
              (.getPath event))))))))
  (.start fk)
  fk)) 

以上就是storm与zookeeper进行交互的源码分析，我觉得最重要的部分就是如何给zk client添加"wacher"，storm的很多功能都是通过zookeeper的wacher机制实现的，如"分配信息领取"。添加"wacher"大概分为以下几个步骤：

mk-distributed-cluster-state函数创建了一个zk client，并通过:watcher给该zk client指定了"wacher"函数，这个"wacher"函数只是简单调用ClusterState的callbacks集合中的函数，这样这个"wacher"函数执行 哪些函数将由ClusterState实例决定
ClusterState实例提供register函数来更新callbacks集合，ClusterState实例被传递给了mk-storm-cluster-state函数，在mk-storm-cluster-state中调用register添加了一个函数(fn [type path] ... )，这个函数实现了"watcher"函数的全部逻辑
mk-storm-cluster-state中注册的函数执行的具体内容由StormClusterState实例决定，对zookeeper节点添加"观察"也是通过StormClusterState实例实现的，这样我们就可以通过StormClusterState实例对我们感兴趣的节点添加"观察"和"回调函数"，当节点或节点数据发生变化后，zk server就会给zk client发送"通知"，zk client中的"wather"函数将被调用，进而我们注册的"回到函数"将被执行。

总结

这部分源码与zookeeper联系十分紧密，涉及了很多zookeeper中的概念和特性，如"数据观察"和"节点观察"等，有关zookeeper的wacher机制请参考：http://www.jb51.net/article/124295.htm，storm并没有直接使用zookeeper的api，而是使用Curator框架，Curator框架简化了访问zookeeper的操作。关于Curator框架请参考：http://www.jb51.net/article/125785.htm。

以上就是本文关于源码阅读之storm操作zookeeper-cluster.clj的全部内容了，感兴趣的朋友可以参阅：zookeeper watch机制的理解、apache zookeeper使用方法实例详解、为zookeeper配置相应的acl权限等，希望对大家有所帮助。感谢各位的阅读！