storm操作zookeeper源码分析-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函数定义如下：
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。

mk-client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：

1. 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

2. 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

3. 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。

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.cnblogs.com/ggjucheng/p/3369946.html
http://www.cnblogs.com/zhangchaoyang/articles/3813217.html
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://f.dataguru.cn/thread-120125-1-1.html