Github user anmolnar commented on a diff in the pull request:
https://github.com/apache/zookeeper/pull/680#discussion_r239143301
--- Diff:
zookeeper-server/src/main/java/org/apache/zookeeper/common/FileChangeWatcher.java
---
@@ -0,0 +1,253 @@
+/**
+ * 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.zookeeper.common;
+
+import com.sun.nio.file.SensitivityWatchEventModifier;
+import org.apache.zookeeper.server.ZooKeeperThread;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.io.IOException;
+import java.nio.file.ClosedWatchServiceException;
+import java.nio.file.FileSystem;
+import java.nio.file.Path;
+import java.nio.file.StandardWatchEventKinds;
+import java.nio.file.WatchEvent;
+import java.nio.file.WatchKey;
+import java.nio.file.WatchService;
+import java.util.function.Consumer;
+
+/**
+ * Instances of this class can be used to watch a directory for file
changes. When a file is added to, deleted from,
+ * or is modified in the given directory, the callback provided by the
user will be called from a background thread.
+ * Some things to keep in mind:
+ * <ul>
+ * <li>The callback should be thread-safe.</li>
+ * <li>Changes that happen around the time the thread is started may be
missed.</li>
+ * <li>There is a delay between a file changing and the callback
firing.</li>
+ * <li>The watch is not recursive - changes to subdirectories will not
trigger a callback.</li>
+ * </ul>
+ */
+public final class FileChangeWatcher {
--- End diff --
Maybe it doesn't make sense, but I'm thinking of whether it would be better
to make `FileChangeWatcher` class the thread itself instead using a "wrapped"
Thread instance. In which case you might not need to forward the `stop()` call,
but can call it directly.
---
