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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CURATOR-33) Recursive Node Cache
Date Fri, 18 Jul 2014 19:08:04 GMT

    [ https://issues.apache.org/jira/browse/CURATOR-33?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14066744#comment-14066744
] 

ASF GitHub Bot commented on CURATOR-33:
---------------------------------------

Github user dragonsinth commented on a diff in the pull request:

    https://github.com/apache/curator/pull/17#discussion_r15128164
  
    --- Diff: curator-recipes/src/main/java/org/apache/curator/framework/recipes/cache/TreeCache.java
---
    @@ -0,0 +1,600 @@
    +/**
    + * 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.curator.framework.recipes.cache;
    +
    +import com.google.common.base.Function;
    +import com.google.common.collect.ImmutableSortedSet;
    +import com.google.common.collect.Maps;
    +import org.apache.curator.framework.CuratorFramework;
    +import org.apache.curator.framework.api.BackgroundCallback;
    +import org.apache.curator.framework.api.CuratorEvent;
    +import org.apache.curator.framework.listen.ListenerContainer;
    +import org.apache.curator.framework.state.ConnectionState;
    +import org.apache.curator.framework.state.ConnectionStateListener;
    +import org.apache.curator.utils.CloseableExecutorService;
    +import org.apache.curator.utils.ThreadUtils;
    +import org.apache.curator.utils.ZKPaths;
    +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;
    +import java.io.Closeable;
    +import java.io.IOException;
    +import java.util.ArrayList;
    +import java.util.Collections;
    +import java.util.List;
    +import java.util.SortedSet;
    +import java.util.concurrent.ConcurrentMap;
    +import java.util.concurrent.ExecutorService;
    +import java.util.concurrent.Executors;
    +import java.util.concurrent.ThreadFactory;
    +import java.util.concurrent.atomic.AtomicLong;
    +import java.util.concurrent.atomic.AtomicReference;
    +
    +/**
    + * <p>A utility that attempts to keep all data from all children of a ZK path locally
cached. This class
    + * will watch the ZK path, respond to update/create/delete events, pull down the data,
etc. You can
    + * register a listener that will get notified when changes occur.</p>
    + * <p></p>
    + * <p><b>IMPORTANT</b> - it's not possible to stay transactionally
in sync. Users of this class must
    + * be prepared for false-positives and false-negatives. Additionally, always use the
version number
    + * when updating data to avoid overwriting another process' change.</p>
    + */
    +public class TreeCache implements Closeable
    +{
    +    private static final Logger LOG = LoggerFactory.getLogger(TreeCache.class);
    +
    +    private enum NodeState
    +    {
    +        PENDING, LIVE, DEAD
    +    }
    +
    +    final class TreeNode implements Watcher, BackgroundCallback
    +    {
    +        private final AtomicReference<NodeState> nodeState = new AtomicReference<NodeState>(NodeState.PENDING);
    +        private final String path;
    +        private final TreeNode parent;
    +        private final AtomicReference<Stat> stat = new AtomicReference<Stat>();
    +        private final AtomicReference<byte[]> data = new AtomicReference<byte[]>();
    +        private final AtomicReference<ConcurrentMap<String, TreeNode>> children
= new AtomicReference<ConcurrentMap<String, TreeNode>>();
    +
    +        TreeNode(String path, TreeNode parent)
    +        {
    +            this.path = path;
    +            this.parent = parent;
    +        }
    +
    +        private void refreshChildren() throws Exception
    +        {
    +            outstandingOps.incrementAndGet();
    +            client.getChildren().usingWatcher(this).inBackground(this).forPath(path);
    +        }
    +
    +        private void refreshData() throws Exception
    +        {
    +            outstandingOps.incrementAndGet();
    +            if ( dataIsCompressed )
    +            {
    +                client.getData().decompressed().usingWatcher(this).inBackground(this).forPath(path);
    +            }
    +            else
    +            {
    +                client.getData().usingWatcher(this).inBackground(this).forPath(path);
    +            }
    +        }
    +
    +        private void wasReconnected() throws Exception
    +        {
    +            refreshData();
    +            refreshChildren();
    +            ConcurrentMap<String, TreeNode> childMap = children.get();
    +            if ( childMap != null )
    +            {
    +                for ( TreeNode child : childMap.values() )
    +                {
    +                    child.wasReconnected();
    +                }
    +            }
    +        }
    +
    +        private void wasCreated() throws Exception
    +        {
    +            refreshData();
    +            refreshChildren();
    +        }
    +
    +        private void wasDeleted() throws Exception
    +        {
    +            stat.set(null);
    +            data.set(null);
    +            client.clearWatcherReferences(this);
    +            ConcurrentMap<String, TreeNode> childMap = children.getAndSet(null);
    +            if ( childMap != null )
    +            {
    +                ArrayList<TreeNode> childCopy = new ArrayList<TreeNode>(childMap.values());
    +                childMap.clear();
    +                for ( TreeNode child : childCopy )
    +                {
    +                    child.wasDeleted();
    +                }
    +            }
    +
    +            if ( treeState.get() == TreeState.CLOSED )
    +            {
    +                return;
    +            }
    +
    +            if ( nodeState.compareAndSet(NodeState.LIVE, NodeState.DEAD) )
    +            {
    +                publishEvent(TreeCacheEvent.Type.NODE_REMOVED, path);
    +            }
    +
    +            if ( parent == null )
    +            {
    +                // Root node; use an exist query to watch for existence.
    +                client.checkExists().usingWatcher(this).inBackground().forPath(path);
    +            }
    +            else
    +            {
    +                // Remove from parent if we're currently a child
    +                ConcurrentMap<String, TreeNode> parentChildMap = parent.children.get();
    +                if ( parentChildMap != null )
    +                {
    +                    parentChildMap.remove(ZKPaths.getNodeFromPath(path), this);
    +                }
    +            }
    +        }
    +
    +        @Override
    +        public void process(WatchedEvent event)
    +        {
    +            System.out.println(event);
    +            try
    +            {
    +                switch ( event.getType() )
    +                {
    +                case NodeCreated:
    +                    assert parent == null;
    +                    wasCreated();
    +                    break;
    +                case NodeChildrenChanged:
    +                    refreshChildren();
    +                    break;
    +                case NodeDataChanged:
    +                    refreshData();
    +                    break;
    +                case NodeDeleted:
    +                    wasDeleted();
    +                    break;
    +                }
    +            }
    +            catch ( Exception e )
    +            {
    +                handleException(e);
    +            }
    +        }
    +
    +        @Override
    +        public void processResult(CuratorFramework client, CuratorEvent event) throws
Exception
    +        {
    +            System.out.println(event);
    +            switch ( event.getType() )
    +            {
    +            case EXISTS:
    +                // TODO: should only happen for root node
    +                if ( event.getResultCode() == KeeperException.Code.OK.intValue() )
    +                {
    +                    nodeState.compareAndSet(NodeState.DEAD, NodeState.PENDING);
    +                    wasCreated();
    +                }
    +                else if ( event.getResultCode() == KeeperException.Code.NONODE.intValue()
)
    +                {
    +                    wasDeleted();
    +                }
    +                break;
    +            case CHILDREN:
    +                if ( event.getResultCode() == KeeperException.Code.OK.intValue() )
    +                {
    +                    stat.set(event.getStat());
    +
    +                    if ( event.getChildren().isEmpty() )
    +                    {
    +                        break;
    +                    }
    +
    +                    ConcurrentMap<String, TreeNode> childMap = children.get();
    +                    if ( childMap == null )
    +                    {
    +                        childMap = Maps.newConcurrentMap();
    +                        if ( !children.compareAndSet(null, childMap) )
    +                        {
    +                            childMap = children.get();
    +                        }
    +                    }
    +
    +                    for ( String child : event.getChildren() )
    +                    {
    +                        String fullPath = ZKPaths.makePath(path, child);
    +                        if ( !childMap.containsKey(child) )
    +                        {
    +                            TreeNode node = new TreeNode(fullPath, this);
    +                            if ( childMap.putIfAbsent(child, node) == null )
    +                            {
    +                                node.wasCreated();
    +                            }
    +                        }
    +                    }
    +                }
    +                else if ( event.getResultCode() == KeeperException.Code.NONODE.intValue()
)
    +                {
    +                    wasDeleted();
    +                }
    +                break;
    +            case GET_DATA:
    +                if ( event.getResultCode() == KeeperException.Code.OK.intValue() )
    +                {
    +                    Stat oldStat = stat.getAndSet(event.getStat());
    +                    if ( cacheData )
    +                    {
    +                        data.set(event.getData());
    +                    }
    +
    +                    if ( nodeState.compareAndSet(NodeState.PENDING, NodeState.LIVE) )
    +                    {
    +                        publishEvent(TreeCacheEvent.Type.NODE_ADDED, new ChildData(event.getPath(),
event.getStat(), event.getData()));
    +                    }
    +                    else if ( oldStat.getMzxid() != event.getStat().getMzxid() )
    +                    {
    +                        publishEvent(TreeCacheEvent.Type.NODE_UPDATED, new ChildData(event.getPath(),
event.getStat(), event.getData()));
    +                    }
    +                }
    +                else if ( event.getResultCode() == KeeperException.Code.NONODE.intValue()
)
    +                {
    +                    wasDeleted();
    +                }
    +                break;
    +            default:
    +                handleException(new Exception(String.format("Unknown event %s", event)));
    +            }
    +
    +            if ( outstandingOps.decrementAndGet() == 0 )
    +            {
    +                if ( treeState.compareAndSet(TreeState.LATENT, TreeState.STARTED) )
    +                {
    +                    publishEvent(TreeCacheEvent.Type.INITIALIZED);
    +                }
    +            }
    +        }
    +    }
    +
    +    private enum TreeState
    +    {
    +        LATENT,
    +        STARTED,
    +        CLOSED
    +    }
    +
    +    /**
    +     * Detemines when to publish the initialized event.
    +     */
    +    private final AtomicLong outstandingOps = new AtomicLong(0);
    +
    +    private final TreeNode root;
    +    private final CuratorFramework client;
    +    private final CloseableExecutorService executorService;
    +    private final boolean cacheData;
    +    private final boolean dataIsCompressed;
    +    private final ListenerContainer<TreeCacheListener> listeners = new ListenerContainer<TreeCacheListener>();
    +    private final AtomicReference<TreeState> treeState = new AtomicReference<TreeState>(TreeState.LATENT);
    +
    +    private final ConnectionStateListener connectionStateListener = new ConnectionStateListener()
    +    {
    +        @Override
    +        public void stateChanged(CuratorFramework client, ConnectionState newState)
    +        {
    +            handleStateChange(newState);
    +        }
    +    };
    +
    +    private static final ThreadFactory defaultThreadFactory = ThreadUtils.newThreadFactory("TreeCache");
    +
    +    /**
    +     * @param client    the client
    +     * @param path      path to watch
    +     * @param cacheData if true, node contents are cached in addition to the stat
    +     */
    +    public TreeCache(CuratorFramework client, String path, boolean cacheData)
    +    {
    +        this(client, path, cacheData, false, new CloseableExecutorService(Executors.newSingleThreadExecutor(defaultThreadFactory),
true));
    +    }
    +
    +    /**
    +     * @param client        the client
    +     * @param path          path to watch
    +     * @param cacheData     if true, node contents are cached in addition to the stat
    +     * @param threadFactory factory to use when creating internal threads
    +     */
    +    public TreeCache(CuratorFramework client, String path, boolean cacheData, ThreadFactory
threadFactory)
    +    {
    +        this(client, path, cacheData, false, new CloseableExecutorService(Executors.newSingleThreadExecutor(threadFactory),
true));
    +    }
    +
    +    /**
    +     * @param client           the client
    +     * @param path             path to watch
    +     * @param cacheData        if true, node contents are cached in addition to the stat
    +     * @param dataIsCompressed if true, data in the path is compressed
    +     * @param threadFactory    factory to use when creating internal threads
    +     */
    +    public TreeCache(CuratorFramework client, String path, boolean cacheData, boolean
dataIsCompressed, ThreadFactory threadFactory)
    +    {
    +        this(client, path, cacheData, dataIsCompressed, new CloseableExecutorService(Executors.newSingleThreadExecutor(threadFactory),
true));
    +    }
    +
    +    /**
    +     * @param client           the client
    +     * @param path             path to watch
    +     * @param cacheData        if true, node contents are cached in addition to the stat
    +     * @param dataIsCompressed if true, data in the path is compressed
    +     * @param executorService  ExecutorService to use for the TreeCache's background
thread
    +     */
    +    public TreeCache(CuratorFramework client, String path, boolean cacheData, boolean
dataIsCompressed, final ExecutorService executorService)
    +    {
    +        this(client, path, cacheData, dataIsCompressed, new CloseableExecutorService(executorService));
    +    }
    +
    +    /**
    +     * @param client           the client
    +     * @param path             path to watch
    +     * @param cacheData        if true, node contents are cached in addition to the stat
    +     * @param dataIsCompressed if true, data in the path is compressed
    +     * @param executorService  Closeable ExecutorService to use for the TreeCache's background
thread
    +     */
    +    public TreeCache(CuratorFramework client, String path, boolean cacheData, boolean
dataIsCompressed, final CloseableExecutorService executorService)
    +    {
    +        this.root = new TreeNode(path, null);
    +        this.client = client;
    +        this.cacheData = cacheData;
    +        this.dataIsCompressed = dataIsCompressed;
    +        this.executorService = executorService;
    +    }
    +
    +    /**
    +     * Start the cache. The cache is not started automatically. You must call this method.
    +     *
    +     * @throws Exception errors
    +     */
    +    public void start() throws Exception
    +    {
    +        client.getConnectionStateListenable().addListener(connectionStateListener);
    +        root.wasCreated();
    +    }
    +
    +    /**
    +     * Close/end the cache
    +     *
    +     * @throws java.io.IOException errors
    +     */
    +    @Override
    +    public void close() throws IOException
    +    {
    +        if ( treeState.compareAndSet(TreeState.STARTED, TreeState.CLOSED) )
    +        {
    +            client.getConnectionStateListenable().removeListener(connectionStateListener);
    +            listeners.clear();
    +            executorService.close();
    +            try
    +            {
    +                root.wasDeleted();
    +            }
    +            catch ( Exception e )
    +            {
    +                handleException(e);
    +            }
    +        }
    +    }
    +
    +    /**
    +     * Return the cache listenable
    +     *
    +     * @return listenable
    +     */
    +    public ListenerContainer<TreeCacheListener> getListenable()
    +    {
    +        return listeners;
    +    }
    +
    +    private TreeNode find(String fullPath)
    +    {
    +        if ( !fullPath.startsWith(root.path) )
    +        {
    +            return null;
    +        }
    +
    +        TreeNode current = root;
    +        if ( fullPath.length() > root.path.length() )
    +        {
    +            List<String> split = ZKPaths.split(fullPath.substring(root.path.length()));
    +            for ( String part : split )
    +            {
    +                ConcurrentMap<String, TreeNode> map = current.children.get();
    +                if ( map == null )
    +                {
    +                    return null;
    +                }
    +                current = map.get(part);
    +                if ( current == null )
    +                {
    +                    return null;
    +                }
    +            }
    +        }
    +        return current;
    +    }
    +
    +    /**
    +     * Return the current set of children. There are no guarantees of accuracy. This
is
    +     * merely the most recent view of the data. The data is returned in sorted order.
If there is
    --- End diff --
    
    To be fair, if you get a child update event it actually includes the data with the event;
but you're right, there's no possible way to ensure the node hasn't been subsequently deleted
by the time you go to query the tree (even in the event callback).
    
    I don't quite see what you're getting at with a slower consistent API short of COW.  Locking
on the consumer side won't do any good unless you're also locking on the mutation side, which
means you're allowing user code to block tree updates-- which seems really bad and could cause
queuing problems on the mutation side while arbitrary callback code is running.
    
    I think the only solution if you really want to see a consistent view is an immutable
copy-on-write tree.  Every update would produce a new root node, and new nodes down to the
point of change, so updates would be O(lg n).  Most of the nodes would be shared between each
tree revision.  Once the new tree is constructed you atomically update the root reference.
 You could actually attach the entire tree state to every event if you wanted.
    
    I agree it's kind of an appealing story, but the reason it seems like overkill to me is
that you can't (generally) get a consistent view of ZK anyway, and I worry about GC pressure
of creating so many objects.  But I could be convince to take a crack at this approach.


> Recursive Node Cache
> --------------------
>
>                 Key: CURATOR-33
>                 URL: https://issues.apache.org/jira/browse/CURATOR-33
>             Project: Apache Curator
>          Issue Type: Improvement
>          Components: Recipes
>            Reporter: John Vines
>             Fix For: awaiting-response
>
>         Attachments: CURATOR-33.2.patch, CURATOR-33.patch
>
>
> Currently the PathChildrenCache will trigger listen events for all children at the given
node. However, it would be useful to have a cache that would trigger listen events for the
entire hierarchy below the given node.



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