ZooKeeperChildrenCache.java

/**
 * Copyright 2016 Yahoo Inc.
 *
 * 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.yahoo.pulsar.zookeeper;

import java.util.List;
import java.util.Set;
import java.util.concurrent.atomic.AtomicBoolean;

import org.apache.zookeeper.KeeperException;
import org.apache.zookeeper.WatchedEvent;
import org.apache.zookeeper.Watcher;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import com.google.common.collect.Lists;
import com.yahoo.pulsar.zookeeper.ZooKeeperCache.CacheUpdater;

/**
 * This class keeps a cache of the children for several z-nodes and updates it whenever it's changed on zookeeper.
 */
public class ZooKeeperChildrenCache implements Watcher, CacheUpdater<Set<String>> {
    private static final Logger LOG = LoggerFactory.getLogger(ZooKeeperChildrenCache.class);

    private final ZooKeeperCache cache;
    private final String path;
    private final List<ZooKeeperCacheListener<Set<String>>> listeners = Lists.newCopyOnWriteArrayList();
    private final AtomicBoolean isShutdown;

    public ZooKeeperChildrenCache(ZooKeeperCache cache, String path) {
        this.cache = cache;
        this.path = path;
        isShutdown = new AtomicBoolean(false);
    }

    public Set<String> get() throws KeeperException, InterruptedException {
        return cache.getChildren(path, this);
    }

    public Set<String> get(String path) throws KeeperException, InterruptedException {
        LOG.debug("getChildren called at: {}", path);
        return cache.getChildren(path, this);
    }

    public void clear() {
        cache.invalidateChildren(path);
    }

    public void clearTree() {
        cache.invalidateRoot(path);
    }

    @Override
    public void reloadCache(final String path) {
        try {
            cache.invalidate(path);
            Set<String> children = cache.getChildren(path, this);
            LOG.info("reloadCache called in zookeeperChildrenCache for path {}", path);
            for (ZooKeeperCacheListener<Set<String>> listener : listeners) {
                listener.onUpdate(path, children, null);
            }
        } catch (KeeperException.NoNodeException nne) {
            LOG.debug("Node [{}] does not exist", nne.getPath());
        } catch (Exception e) {
            LOG.warn("Reloading ZooKeeperDataCache failed at path:{}", path);
        }
    }

    @Override
    public void registerListener(ZooKeeperCacheListener<Set<String>> listener) {
        listeners.add(listener);
    }

    @Override
    public void unregisterListener(ZooKeeperCacheListener<Set<String>> listener) {
        listeners.remove(listener);
    }

    @Override
    public void process(WatchedEvent event) {
        LOG.debug("[{}] Received ZooKeeper watch event: {}", cache.zkSession.get(), event);
        if (!isShutdown.get()) {
            cache.process(event, this);
        }
    }

    public void close() {
        isShutdown.set(true);
    }
}