Storm-源码分析- Multimethods使用例子

1. storm通过multimethods来区分local和distributed模式

当调用launch-worker的时候, clojure会自动根据defmulti里面定义的fn来判断是调用哪个版本的launch-worker

 

(defmulti launch-worker (fn [supervisor & _] (cluster-mode (:conf supervisor))))

 

(defmethod launch-worker

    :distributed [supervisor storm-id port worker-id]

    (let [conf (:conf supervisor)

          storm-home (System/getProperty "storm.home")

          stormroot (supervisor-stormdist-root conf storm-id)

          stormjar (supervisor-stormjar-path stormroot)

          storm-conf (read-supervisor-storm-conf conf storm-id)

          classpath (add-to-classpath (current-classpath) [stormjar])

          childopts (.replaceAll (str (conf WORKER-CHILDOPTS) " " (storm-conf TOPOLOGY-WORKER-CHILDOPTS))

                                 "%ID%"

                                 (str port))

          logfilename (str "worker-" port ".log")

          command (str "java -server " childopts

                       " -Djava.library.path=" (conf JAVA-LIBRARY-PATH)

                       " -Dlogfile.name=" logfilename

                       " -Dstorm.home=" storm-home

                       " -Dlogback.configurationFile=" storm-home "/logback/cluster.xml"

                       " -cp " classpath " backtype.storm.daemon.worker "

                       (java.net.URLEncoder/encode storm-id) " " (:assignment-id supervisor)

                       " " port " " worker-id)]

      (log-message "Launching worker with command: " command)

      (launch-process command :environment {"LD_LIBRARY_PATH" (conf JAVA-LIBRARY-PATH)})

      ))

(defmethod launch-worker

    :local [supervisor storm-id port worker-id]

    (let [conf (:conf supervisor)

          pid (uuid)

          worker (worker/mk-worker conf

                                   (:shared-context supervisor)

                                   storm-id

                                   (:assignment-id supervisor)

                                   port

                                   worker-id)]

      (psim/register-process pid worker)

      (swap! (:worker-thread-pids-atom supervisor) assoc worker-id pid)

      ))

2. storm通过multimethods来区分blot和spout

在executor.clj中通过multimethods来区分blot和spout不同的创建逻辑

(defmulti mk-threads executor-selector)

(defmulti mk-executor-stats executor-selector)

(defmulti close-component executor-selector)