zk的EventThread毒药

最新推荐文章于 2022-03-17 08:09:07 发布

原创最新推荐文章于 2022-03-17 08:09:07 发布 · 1.1k 阅读

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本文深入探讨了zk-client中EventThread的工作原理及其关键组件，包括事件队列管理、状态更新及事件处理流程等核心内容。

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zk-client EventThread 通过eventOfDeath 停止

class EventThread extends ZooKeeperThread {
        private final LinkedBlockingQueue<Object> waitingEvents =
            new LinkedBlockingQueue<Object>();

        /** This is really the queued session state until the event
         * thread actually processes the event and hands it to the watcher.
         * But for all intents and purposes this is the state.
         */
        private volatile KeeperState sessionState = KeeperState.Disconnected;

       private volatile boolean wasKilled = false;
       private volatile boolean isRunning = false;

        EventThread() {
            super(makeThreadName("-EventThread"));
            setDaemon(true);
        }

        public void queueEvent(WatchedEvent event) {
            if (event.getType() == EventType.None
                    && sessionState == event.getState()) {
                return;
            }
            sessionState = event.getState();

            // materialize the watchers based on the event
            WatcherSetEventPair pair = new WatcherSetEventPair(
                    watcher.materialize(event.getState(), event.getType(),
                            event.getPath()),
                            event);
            // queue the pair (watch set & event) for later processing
            waitingEvents.add(pair);
        }

       public void queuePacket(Packet packet) {
          if (wasKilled) {
             synchronized (waitingEvents) {
                if (isRunning) waitingEvents.add(packet);
                else processEvent(packet);
             }
          } else {
             waitingEvents.add(packet);
          }
       }

        public void queueEventOfDeath() {
            waitingEvents.add(eventOfDeath);
        }

        @Override
        public void run() {
           try {
              isRunning = true;
              while (true) {
                 Object event = waitingEvents.take();
                 if (event == eventOfDeath) {
                    wasKilled = true;
                 } else {
                    processEvent(event);
                 }
                 if (wasKilled)
                    synchronized (waitingEvents) {
                       if (waitingEvents.isEmpty()) {
                          isRunning = false;
                          break;
                       }
                    }
              }
           } catch (InterruptedException e) {
              LOG.error("Event thread exiting due to interruption", e);
           }

            LOG.info("EventThread shut down for session: 0x{}",
                     Long.toHexString(getSessionId()));
        }
        ```