Github user cconroy commented on a diff in the pull request:
https://github.com/apache/curator/pull/17#discussion_r15123089
--- 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
--- End diff --
I know this comment comes form path and node cache, but I find it very
unhelpful. I think it would be more clear to note that a sequence of updates to
any two nodes may be delivered in any sequence by the cache.
But, it also seems like we should be able to offer a much stronger
consistency guarantee. Watches are guaranteed to fire in order from the ZK
protocol level, and therefore we should be able to give consistent delivery of
e.g. a recursive delete bottom up, tree creation top-down, etc. TreeCache is
potentially in a much better position to do this since it need not segment the
listener for each path into its own single threaded executor.
The only major caveat I see here is on a disconnect/reconnect case where we
have to re-read the tree, but the events could still be synthesized in correct
tree order for add/remove.
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