ZooKeeperDataCache.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.Map.Entry;
import java.util.Optional;
import java.util.concurrent.CompletableFuture;
import java.util.concurrent.atomic.AtomicBoolean;
import java.util.concurrent.atomic.AtomicIntegerFieldUpdater;

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

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

/**
 * Provides a generic cache for reading objects stored in zookeeper.
 *
 * Maintains the objects already serialized in memory and sets watches to receive changes notifications.
 *
 * @param <T>
 */
public abstract class ZooKeeperDataCache<T> implements Deserializer<T>, CacheUpdater<T>, Watcher {
    private static final Logger LOG = LoggerFactory.getLogger(ZooKeeperDataCache.class);

    private final ZooKeeperCache cache;
    private final List<ZooKeeperCacheListener<T>> listeners = Lists.newCopyOnWriteArrayList();

    private static final int FALSE = 0;
    private static final int TRUE = 1;

    private static final AtomicIntegerFieldUpdater<ZooKeeperDataCache> IS_SHUTDOWN_UPDATER = AtomicIntegerFieldUpdater
            .newUpdater(ZooKeeperDataCache.class, "isShutdown");
    private volatile int isShutdown = FALSE;

    public ZooKeeperDataCache(final ZooKeeperCache cache) {
        this.cache = cache;
    }

    public CompletableFuture<Optional<T>> getAsync(String path) {
        CompletableFuture<Optional<T>> future = new CompletableFuture<>();
        cache.getDataAsync(path, this, this).thenAccept(entry -> {
            future.complete(entry.map(Entry::getKey));
        }).exceptionally(ex -> {
            cache.asyncInvalidate(path);
            future.completeExceptionally(ex);
            return null;
        });

        return future;
    }

    /**
     * Return an item from the cache
     *
     * If node doens't exist, the value will be not present.s
     *
     * @param path
     * @return
     * @throws Exception
     */
    public Optional<T> get(final String path) throws Exception {
        return getWithStat(path).map(Entry::getKey);
    }

    public Optional<Entry<T, Stat>> getWithStat(final String path) throws Exception {
        return cache.getData(path, this, this);
    }

    /**
     * Only for UTs (for now), as this clears the whole ZK data cache.
     */
    public void clear() {
        cache.invalidateAllData();
    }

    public void invalidate(final String path) {
        cache.invalidateData(path);
    }

    @Override
    public void reloadCache(final String path) {
        try {
            if (LOG.isDebugEnabled()) {
                LOG.debug("Reloading ZooKeeperDataCache at path {}", path);
            }
            cache.invalidate(path);
            Optional<Entry<T, Stat>> cacheEntry = cache.getData(path, this, this);
            if (!cacheEntry.isPresent()) {
                if (LOG.isDebugEnabled()) {
                    LOG.debug("Node [{}] does not exist", path);
                }
                return;
            }

            for (ZooKeeperCacheListener<T> listener : listeners) {
                if (LOG.isDebugEnabled()) {
                    LOG.debug("Notifying listener {} at path {}", listener, path);
                }
                listener.onUpdate(path, cacheEntry.get().getKey(), cacheEntry.get().getValue());
                if (LOG.isDebugEnabled()) {
                    LOG.debug("Notified listener {} at path {}", listener, path);
                }
            }
        } catch (Exception e) {
            LOG.warn("Reloading ZooKeeperDataCache failed at path: {}", path, e);
        }
    }

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

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

    @Override
    public void process(WatchedEvent event) {
        LOG.info("[{}] Received ZooKeeper watch event: {}", cache.zkSession.get(), event);
        if (IS_SHUTDOWN_UPDATER.get(this) == FALSE) {
            cache.process(event, this);
        }
    }

    public void close() {
        IS_SHUTDOWN_UPDATER.set(this, TRUE);
    }
}