content: /**
   * Copyright 2010 the original author or authors.
   *
   * Licensed 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.
   */
  package com.github.zkclient;
  
  import java.util.concurrent.BlockingQueue;
  import java.util.concurrent.LinkedBlockingQueue;
  import java.util.concurrent.atomic.AtomicInteger;
  
  
  import com.github.zkclient.exception.ZkInterruptedException;
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  /**
   * All listeners registered at the {@link ZkClient} will be notified from this event thread.
   * This is to prevent dead-lock situations. The {@link ZkClient} pulls some information out of
   * the {@link org.apache.zookeeper.ZooKeeper} events to signal {@link ZkLock} conditions. Re-using the
   * {@link org.apache.zookeeper.ZooKeeper} event thread to also notify {@link ZkClient} listeners, would stop the
   * ZkClient from receiving events from {@link org.apache.zookeeper.ZooKeeper} as soon as one of the listeners blocks
   * (because it is waiting for something). {@link ZkClient} would then for instance not be able
   * to maintain it's connection state anymore.
   */
  class ZkEventThread extends Thread {
  
      private static final Logger LOG = LoggerFactory.getLogger(ZkEventThread.class);
  
      private final BlockingQueue<ZkEvent> _events = new LinkedBlockingQueue<ZkEvent>();
  
      private static final AtomicInteger _eventId = new AtomicInteger(0);
  
      private volatile boolean shutdown = false;
  
      static abstract class ZkEvent {
  
          private final String _description;
  
          public ZkEvent(String description) {
              _description = description;
          }
  
          public abstract void run() throws Exception;
  
          @Override
          public String toString() {
              return "ZkEvent[" + _description + "]";
          }
      }
  
      ZkEventThread(String name) {
          setDaemon(true);
          setName("ZkClient-EventThread-" + getId() + "-" + name);
      }
  
      @Override
      public void run() {
          LOG.info("Starting ZkClient event thread.");
          try {
              while (!isShutdown()) {
                  ZkEvent zkEvent = _events.take();
                  int eventId = _eventId.incrementAndGet();
                  LOG.debug("Delivering event #" + eventId + " " + zkEvent);
                  try {
                      zkEvent.run();
                  } catch (InterruptedException e) {
                      shutdown();
                  } catch (ZkInterruptedException e) {
                      shutdown();
                  } catch (Throwable e) {
                      LOG.error("Error handling event " + zkEvent, e);
                  }
                  LOG.debug("Delivering event #" + eventId + " done");
              }
          } catch (InterruptedException e) {
              LOG.info("Terminate ZkClient event thread.");
          }
      }
  
      /**
       * @return the shutdown
       */
      public boolean isShutdown() {
          return shutdown || isInterrupted();
      }
  
      public void shutdown() {
          this.shutdown = true;
          this.interrupt();
      }
  
      public void send(ZkEvent event) {
          if (!isShutdown()) {
              LOG.debug("New event: " + event);
              _events.add(event);
          }
      }
  }
  