Storm-源码分析- hook (backtype.storm.hooks)

task hook

在某些task事件发生时, 如果用户希望执行一些额外的逻辑, 就需要使用hook

当前定义如下事件, emit, cleanup, spoutAck……

用户只需要开发实现ITaskHook的类, 并将类名配置到(storm-conf TOPOLOGY-AUTO-TASK-HOOKS)

系统会在这些事件发生时, 自动调用所有注册的hook中的相应的functions

public interface ITaskHook {
    void prepare(Map conf, TopologyContext context);
    void cleanup();
    void emit(EmitInfo info);
    void spoutAck(SpoutAckInfo info);
    void spoutFail(SpoutFailInfo info);
    void boltExecute(BoltExecuteInfo info);
    void boltAck(BoltAckInfo info);
    void boltFail(BoltFailInfo info);
}

public class EmitInfo {
    public List<Object> values;
    public String stream;
    public int taskId;
    public Collection<Integer> outTasks;

    public EmitInfo(List<Object> values, String stream, int taskId, Collection<Integer> outTasks) {
        this.values = values;
        this.stream = stream;
        this.taskId = taskId;
        this.outTasks = outTasks;
    }
}

1. add hook

在mk-task的时候, 会从storm-conf配置里面读出hooks的class names 
创建hook对象, 加入到TopologyContext的_hooks中

(defn mk-task [executor-data task-id]
    (doseq [klass (storm-conf TOPOLOGY-AUTO-TASK-HOOKS)]
      (.addTaskHook ^TopologyContext (:user-context task-data) (-> klass Class/forName .newInstance)))
)

public class TopologyContext extends WorkerTopologyContext implements IMetricsContext {
    private List<ITaskHook> _hooks = new ArrayList<ITaskHook>();

    public void addTaskHook(ITaskHook hook) {
        hook.prepare(_stormConf, this);
        _hooks.add(hook);
    }

    public Collection<ITaskHook> getHooks() {
        return _hooks;
    }
}

2. apply hook

当发生相应的事件时, 调用事先注册的hooks

下面的例子是在emit时, 调用相应的hooks 
apply-hooks宏实现也很简单, 从topology context中取出hooks列表, 对每个hook调用emit(EmitInfo)

(apply-hooks user-context .emit (EmitInfo. values stream task-id out-tasks))

(defmacro apply-hooks [topology-context method-sym info-form]
  (let [hook-sym (with-meta (gensym "hook") {:tag 'backtype.storm.hooks.ITaskHook})]
    `(let [hooks# (get-context-hooks ~topology-context)]
       (when-not (hooks-empty? hooks#)
         (let [info# ~info-form]
           (fast-list-iter [~hook-sym hooks#]
             (~method-sym ~hook-sym info#)
             ))))))

本文章摘自博客园，原文发布日期：2013-07-30