storm-core/src/clj/backtype/storm/event.clj

;; Licensed to the Apache Software Foundation (ASF) under one
;; or more contributor license agreements.  See the NOTICE file
;; distributed with this work for additional information
;; regarding copyright ownership.  The ASF licenses this file
;; to you under the Apache License, Version 2.0 (the
;; "License"); you may not use this file except in compliance
;; with the License.  You may obtain a copy of the License at
;;
;; http://www.apache.org/licenses/LICENSE-2.0
;;
;; Unless required by applicable law or agreed to in writing, software
;; distributed under the License is distributed on an "AS IS" BASIS,
;; WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
;; See the License for the specific language governing permissions and
;; limitations under the License.

(ns backtype.storm.event
  (:use [backtype.storm log util])
  (:import [backtype.storm.utils Time Utils])
  (:import [java.io InterruptedIOException])
  (:import [java.util.concurrent LinkedBlockingQueue TimeUnit]))

(defprotocol EventManager
  (add [this event-fn])
  (waiting? [this])
  (shutdown [this]))

(defn event-manager
  "Creates a thread to respond to events. Any error will cause process to halt"
  [daemon?]
  (let [added (atom 0)
        processed (atom 0)
        ^LinkedBlockingQueue queue (LinkedBlockingQueue.)
        running (atom true)
        runner (Thread.
                 (fn []
                   (try-cause
                     (while @running
                       (let [r (.take queue)]
                         (r)
                         (swap! processed inc)))
                     (catch InterruptedIOException t
                       (log-message "Event manager interrupted while doing IO"))
                     (catch InterruptedException t
                       (log-message "Event manager interrupted"))
                     (catch Throwable t
                       (log-error t "Error when processing event")
                       (exit-process! 20 "Error when processing an event")))))]
    (.setDaemon runner daemon?)
    (.start runner)
    (reify
      EventManager

      (add
        [this event-fn]
        ;; should keep track of total added and processed to know if this is finished yet
        (when-not @running
          (throw (RuntimeException. "Cannot add events to a shutdown event manager")))
        (swap! added inc)
        (.put queue event-fn))

      (waiting?
        [this]
        (or (Time/isThreadWaiting runner)
            (= @processed @added)))

      (shutdown
        [this]
        (reset! running false)
        (.interrupt runner)
        (.join runner)))))