content: /*
   * 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.
   */
  package org.apache.distributedlog.impl;
  
  import static org.apache.distributedlog.util.DLUtils.isReservedStreamName;
  
  import java.net.URI;
  import java.util.ArrayList;
  import java.util.List;
  import java.util.concurrent.RejectedExecutionException;
  import java.util.concurrent.TimeUnit;
  import java.util.concurrent.atomic.AtomicBoolean;
  import org.apache.bookkeeper.common.util.OrderedScheduler;
  import org.apache.distributedlog.DistributedLogConfiguration;
  import org.apache.distributedlog.ZooKeeperClient;
  import org.apache.distributedlog.callback.NamespaceListener;
  import org.apache.distributedlog.namespace.NamespaceWatcher;
  import org.apache.zookeeper.AsyncCallback;
  import org.apache.zookeeper.KeeperException;
  import org.apache.zookeeper.WatchedEvent;
  import org.apache.zookeeper.Watcher;
  import org.apache.zookeeper.data.Stat;
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  
  
  /**
   * Watcher on watching a given namespace.
   */
  public class ZKNamespaceWatcher extends NamespaceWatcher
          implements Runnable, Watcher, AsyncCallback.Children2Callback {
  
      private static final Logger logger = LoggerFactory.getLogger(ZKNamespaceWatcher.class);
  
      private final DistributedLogConfiguration conf;
      private final URI uri;
      private final ZooKeeperClient zkc;
      private final OrderedScheduler scheduler;
      private final AtomicBoolean namespaceWatcherSet = new AtomicBoolean(false);
  
      public ZKNamespaceWatcher(DistributedLogConfiguration conf,
                                URI uri,
                                ZooKeeperClient zkc,
                                OrderedScheduler scheduler) {
          this.conf = conf;
          this.uri = uri;
          this.zkc = zkc;
          this.scheduler = scheduler;
      }
  
      private void scheduleTask(Runnable r, long ms) {
          try {
              scheduler.schedule(r, ms, TimeUnit.MILLISECONDS);
          } catch (RejectedExecutionException ree) {
              logger.error("Task {} scheduled in {} ms is rejected : ", r, ms, ree);
          }
      }
  
      @Override
      public void run() {
          try {
              doWatchNamespaceChanges();
          } catch (Exception e) {
              logger.error("Encountered unknown exception on watching namespace {} ", uri, e);
          }
      }
  
      public void watchNamespaceChanges() {
          if (!namespaceWatcherSet.compareAndSet(false, true)) {
              return;
          }
          doWatchNamespaceChanges();
      }
  
      private void doWatchNamespaceChanges() {
          try {
              zkc.get().getChildren(uri.getPath(), this, this, null);
          } catch (ZooKeeperClient.ZooKeeperConnectionException e) {
              scheduleTask(this, conf.getZKSessionTimeoutMilliseconds());
          } catch (InterruptedException e) {
              Thread.currentThread().interrupt();
              logger.warn("Interrupted on watching namespace changes for {} : ", uri, e);
              scheduleTask(this, conf.getZKSessionTimeoutMilliseconds());
          }
      }
  
      @Override
      public void processResult(int rc, String path, Object ctx, List<String> children, Stat stat) {
          if (KeeperException.Code.OK.intValue() == rc) {
              logger.info("Received updated logs under {} : {}", uri, children);
              List<String> result = new ArrayList<String>(children.size());
              for (String s : children) {
                  if (isReservedStreamName(s)) {
                      continue;
                  }
                  result.add(s);
              }
              for (NamespaceListener listener : listeners) {
                  listener.onStreamsChanged(result.iterator());
              }
          } else {
              scheduleTask(this, conf.getZKSessionTimeoutMilliseconds());
          }
      }
  
      @Override
      public void process(WatchedEvent event) {
          if (event.getType() == Event.EventType.None) {
              if (event.getState() == Event.KeeperState.Expired) {
                  scheduleTask(this, conf.getZKSessionTimeoutMilliseconds());
              }
              return;
          }
          if (event.getType() == Event.EventType.NodeChildrenChanged) {
              // watch namespace changes again.
              doWatchNamespaceChanges();
          }
      }
  }
  