mk-task, 比较简单, 因为task只是概念上的结构, 不象其他worker, executor都需要创建进程或线程 
所以其核心其实就是mk-task-data, 
1. 创建TopologyContext对象, 其实就是把之前的topology对象和worker-data混合到一起, 便于task在执行时可以取到需要的topology信息. 
2. 创建task-object, spout-object或bolt-object, 封装相应的逻辑, 如nextTuple, execute 
3. 生成tasks-fn, 名字起的不好,让人误解执行了task的功能, 其实就是做些emit之间的准备工作, 其中最重要的就是调用grouper去产生targets task, 当然还包含些metrics, hooks的调用.

说白了其实mk-tasks, 没做啥事

(defn mk-task [executor-data task-id]
  (let [task-data (mk-task-data executor-data task-id)  ;;1 mk-task-data  
        storm-conf (:storm-conf executor-data)]
    (doseq [klass (storm-conf TOPOLOGY-AUTO-TASK-HOOKS)] ;; add预定义的hooks
      (.addTaskHook ^TopologyContext (:user-context task-data) (-> klass Class/forName .newInstance)))
    ;; when this is called, the threads for the executor haven't been started yet,
    ;; so we won't be risking trampling on the single-threaded claim strategy disruptor queue
    (send-unanchored task-data SYSTEM-STREAM-ID ["startup"])  ;;向SYSTEM-STREAM, 发送startup通知,谁会接收SYSTEM-STREAM…?
    task-data
    ))

1 mk-task-data

(defn mk-task-data [executor-data task-id]
  (recursive-map
    :executor-data executor-data
    :task-id task-id
    :system-context (system-topology-context (:worker executor-data) executor-data task-id)
    :user-context (user-topology-context (:worker executor-data) executor-data task-id)
    :builtin-metrics (builtin-metrics/make-data (:type executor-data))
    :tasks-fn (mk-tasks-fn <>)
    :object (get-task-object (.getRawTopology ^TopologyContext (:system-context <>)) (:component-id executor-data))))

1.1 TopologyContext

Storm-源码分析-Topology Submit-Task-TopologyContext

:system-context, :user-context, 只是context中的topology对象不同, system为system-topology!

1.2 builtin-metrics/make-data

这里的builtin-metrics用来记录spout或bolt的执行状况的metrics

1.3 mk-tasks-fn

返回tasks-fn, 这个函数主要用于做emit之前的准备工作, 返回target tasks list 
1. 调用grouper, 产生target tasks 
2. 执行emit hook 
3. 满足sampler条件时, 更新stats和buildin-metrics

task-fn, 两种不同参数版本

[^String stream ^List values], 这个版本好理解些, 就是将stream对应的component的target tasks都算上(一个stream可能有多个out component, 一份数据需要发到多个bolt处理)

[^Integer out-task-id ^String stream ^List values], 指定out-task-id, 即direct grouping 
这里对out-task-id做了验证 
out-task-id (if grouping out-task-id), 即out-task-id->component->grouper不为nil(为:direct?), 即验证这个stream确实有到该out-task-id对应component 
如果验证失败, 将out-task-id置nil

(defn mk-tasks-fn [task-data]
  (let [task-id (:task-id task-data)
        executor-data (:executor-data task-data)
        component-id (:component-id executor-data)
        ^WorkerTopologyContext worker-context (:worker-context executor-data)
        storm-conf (:storm-conf executor-data)
        emit-sampler (mk-stats-sampler storm-conf)
        stream->component->grouper (:stream->component->grouper executor-data) ;;Storm-源码分析-Streaming Grouping
        user-context (:user-context task-data)
        executor-stats (:stats executor-data)
        debug? (= true (storm-conf TOPOLOGY-DEBUG))]
        
    (fn ([^Integer out-task-id ^String stream ^List values]
          (when debug?
            (log-message "Emitting direct: " out-task-id "; " component-id " " stream " " values))
          (let [target-component (.getComponentId worker-context out-task-id)
                component->grouping (get stream->component->grouper stream)
                grouping (get component->grouping target-component)
                out-task-id (if grouping out-task-id)]
            (when (and (not-nil? grouping) (not= :direct grouping))
              (throw (IllegalArgumentException. "Cannot emitDirect to a task expecting a regular grouping")))                          
            (apply-hooks user-context .emit (EmitInfo. values stream task-id [out-task-id]))
            (when (emit-sampler)
              (builtin-metrics/emitted-tuple! (:builtin-metrics task-data) executor-stats stream)
              (stats/emitted-tuple! executor-stats stream)
              (if out-task-id
                (stats/transferred-tuples! executor-stats stream 1)
                (builtin-metrics/transferred-tuple! (:builtin-metrics task-data) executor-stats stream 1)))
            (if out-task-id [out-task-id])
            ))
        ([^String stream ^List values]
           (when debug?
             (log-message "Emitting: " component-id " " stream " " values))
           (let [out-tasks (ArrayList.)]
             (fast-map-iter [[out-component grouper] (get stream->component->grouper stream)]
               (when (= :direct grouper)
                  ;;  TODO: this is wrong, need to check how the stream was declared
                  (throw (IllegalArgumentException. "Cannot do regular emit to direct stream")))
               (let [comp-tasks (grouper task-id values)] ;;执行grouper, 产生target tasks
                 (if (or (sequential? comp-tasks) (instance? Collection comp-tasks))
                   (.addAll out-tasks comp-tasks)
                   (.add out-tasks comp-tasks)
                   )))
             (apply-hooks user-context .emit (EmitInfo. values stream task-id out-tasks)) ;;执行事先注册的emit hook
             (when (emit-sampler)    ;;满足抽样条件时, 更新stats和buildin-metrics中的emitted和transferred metric
               (stats/emitted-tuple! executor-stats stream)
               (builtin-metrics/emitted-tuple! (:builtin-metrics task-data) executor-stats stream)              
               (stats/transferred-tuples! executor-stats stream (count out-tasks))
               (builtin-metrics/transferred-tuple! (:builtin-metrics task-data) executor-stats stream (count out-tasks)))
             out-tasks)))
    ))

1.4 get-task-object

取出component的对象, 
比如对于Spout, 取出SpoutSpec中的ComponentObject spout_object, 包含了spout的逻辑, 比如nextTuple()

(defn- get-task-object [^TopologyContext topology component-id]
  (let [spouts (.get_spouts topology)
        bolts (.get_bolts topology)
        state-spouts (.get_state_spouts topology)
        obj (Utils/getSetComponentObject
             (cond
              (contains? spouts component-id) (.get_spout_object ^SpoutSpec (get spouts component-id))
              (contains? bolts component-id) (.get_bolt_object ^Bolt (get bolts component-id))
              (contains? state-spouts component-id) (.get_state_spout_object ^StateSpoutSpec (get state-spouts component-id))
              true (throw-runtime "Could not find " component-id " in " topology)))
        obj (if (instance? ShellComponent obj)
              (if (contains? spouts component-id)
                (ShellSpout. obj)
                (ShellBolt. obj))
              obj )
        obj (if (instance? JavaObject obj)
              (thrift/instantiate-java-object obj)
              obj )]
    obj
    ))

本文章摘自博客园，原文发布日期：2013-07-31