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From tumativ <...@git.apache.org>
Subject [GitHub] zookeeper pull request #680: ZOOKEEPER-3174: Quorum TLS - support reloading ...
Date Sun, 04 Nov 2018 00:58:44 GMT
Github user tumativ commented on a diff in the pull request:

    https://github.com/apache/zookeeper/pull/680#discussion_r230572268
  
    --- Diff: zookeeper-server/src/main/java/org/apache/zookeeper/common/FileChangeWatcher.java
---
    @@ -0,0 +1,191 @@
    +/**
    + * 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 {
    +    private static final Logger LOG = LoggerFactory.getLogger(FileChangeWatcher.class);
    +
    +    public enum State {
    +        NEW,      // object created but start() not called yet
    +        STARTING, // start() called but background thread has not entered main loop
    +        RUNNING,  // background thread is running
    +        STOPPING, // stop() called but background thread has not exited main loop
    +        STOPPED   // stop() called and background thread has exited, or background thread
crashed
    +    }
    +
    +    private final WatcherThread watcherThread;
    +    private State state; // protected by synchronized(this)
    +
    +    /**
    +     * Creates a watcher that watches <code>dirPath</code> and invokes <code>callback</code>
on changes.
    +     *
    +     * @param dirPath the directory to watch.
    +     * @param callback the callback to invoke with events. <code>event.kind()</code>
will return the type of event,
    +     *                 and <code>event.context()</code> will return the filename
relative to <code>dirPath</code>.
    +     * @throws IOException if there is an error creating the WatchService.
    +     */
    +    public FileChangeWatcher(Path dirPath, Consumer<WatchEvent<?>> callback)
throws IOException {
    +        FileSystem fs = dirPath.getFileSystem();
    +        WatchService watchService = fs.newWatchService();
    +        if (LOG.isDebugEnabled()) {
    +            LOG.debug("Registering with watch service: " + dirPath);
    +        }
    +        dirPath.register(
    +                watchService,
    +                new WatchEvent.Kind<?>[]{
    +                        StandardWatchEventKinds.ENTRY_CREATE,
    +                        StandardWatchEventKinds.ENTRY_DELETE,
    +                        StandardWatchEventKinds.ENTRY_MODIFY,
    +                        StandardWatchEventKinds.OVERFLOW},
    +                SensitivityWatchEventModifier.HIGH);
    +        state = State.NEW;
    +        this.watcherThread = new WatcherThread(watchService, callback);
    +        this.watcherThread.setDaemon(true);
    +    }
    +
    +    public synchronized State getState() {
    +        return state;
    +    }
    +
    +    private synchronized void setState(State newState) {
    +        state = newState;
    +        this.notifyAll();
    +    }
    +
    +    /**
    +     * Tells the background thread to start. Does not wait for it to be running.
    +     * Calling this method more than once has no effect.
    +     */
    +    public synchronized void start() {
    +        if (state != State.NEW) {
    +            return;
    +        }
    +        setState(State.STARTING);
    +        this.watcherThread.start();
    +    }
    +
    +    /**
    +     * Tells the background thread to stop. Does not wait for it to exit.
    +     */
    +    public synchronized void stop() {
    +        if (state == State.STARTING || state == State.RUNNING) {
    +            setState(State.STOPPING);
    +            watcherThread.interrupt();
    +        }
    +    }
    +
    +    /**
    +     * Inner class that implements the watcher thread logic.
    +     */
    +    private class WatcherThread extends ZooKeeperThread {
    +        private static final String THREAD_NAME = "FileChangeWatcher";
    +
    +        final WatchService watchService;
    +        final Consumer<WatchEvent<?>> callback;
    +
    +        WatcherThread(WatchService watchService, Consumer<WatchEvent<?>>
callback) {
    +            super(THREAD_NAME);
    +            this.watchService = watchService;
    +            this.callback = callback;
    +        }
    +
    +        @Override
    +        public void run() {
    +            try {
    +                LOG.info(getName() + " thread started");
    +                synchronized (FileChangeWatcher.this) {
    --- End diff --
    
    My intention was, checking and state transition logic can be moved to setState as It is
the entry point to change, state transition needs to be managed here.
    
    The below can be moved to setState
    
    if (FileChangeWatcher.this.getState() == FileChangeWatcher.State.STARTING) {
     state = FileChangeWatcher.State.RUNNING;
    }
    
    we can simply check state is RUNNING or not to proceed further in the run method. 
    
    
    



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