org.apache.blur.zookeeper.WatchChildren.java Source code

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Here is the source code for org.apache.blur.zookeeper.WatchChildren.java

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package org.apache.blur.zookeeper;

/**
 * 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.
 */
import java.io.Closeable;
import java.io.PrintWriter;
import java.io.StringWriter;
import java.util.List;
import java.util.UUID;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicBoolean;

import org.apache.blur.log.Log;
import org.apache.blur.log.LogFactory;
import org.apache.zookeeper.KeeperException;
import org.apache.zookeeper.KeeperException.Code;
import org.apache.zookeeper.WatchedEvent;
import org.apache.zookeeper.Watcher;
import org.apache.zookeeper.ZooKeeper;

public class WatchChildren implements Closeable {

    private final static Log LOG = LogFactory.getLog(WatchChildren.class);
    private final ZooKeeper _zooKeeper;
    private final String _path;
    private final Object _lock = new Object();
    private final AtomicBoolean _running = new AtomicBoolean(true);
    private long _delay = TimeUnit.SECONDS.toMillis(3);
    private List<String> _children;
    private final String instance = UUID.randomUUID().toString();
    private Thread _doubleCheckThread;
    private Thread _watchThread;
    private final boolean _debug = true;
    private String _debugStackTrace;

    public static abstract class OnChange {
        public abstract void action(List<String> children);
    }

    public WatchChildren(ZooKeeper zooKeeper, String path) {
        _zooKeeper = zooKeeper;
        _path = path;
        LOG.debug("Creating watch [{0}]", instance);
    }

    public WatchChildren watch(final OnChange onChange) {
        return watch(onChange, 0, TimeUnit.SECONDS);
    }

    public WatchChildren watch(final OnChange onChange, long fireAnywayTime, TimeUnit timeUnit) {
        if (_debug) {
            StringWriter writer = new StringWriter();
            PrintWriter printWriter = new PrintWriter(writer);
            new Throwable().printStackTrace(printWriter);
            printWriter.close();
            _debugStackTrace = writer.toString();
        }
        final long timeToFireAnywayTime = TimeUnit.MILLISECONDS.convert(fireAnywayTime, timeUnit);
        _watchThread = new Thread(new Runnable() {
            @Override
            public void run() {
                Watcher watcher = new Watcher() {
                    @Override
                    public void process(WatchedEvent event) {
                        synchronized (_lock) {
                            _lock.notify();
                        }
                    }
                };
                startDoubleCheckThread();
                while (_running.get()) {
                    synchronized (_lock) {
                        try {
                            List<String> children = _zooKeeper.getChildren(_path, watcher);
                            try {
                                onChange.action(children);
                                _children = children;
                            } catch (Throwable t) {
                                LOG.error("Unknown error during onchange action [" + this + "].", t);
                            }
                            _lock.wait(timeToFireAnywayTime);
                        } catch (KeeperException e) {
                            if (!_running.get()) {
                                LOG.info("Error [{0}]", e.getMessage());
                                return;
                            }
                            if (e.code() == Code.NONODE) {
                                if (_debug) {
                                    LOG.debug("Path for watching not found [{0}], no longer watching, debug [{1}].",
                                            _path, _debugStackTrace);
                                } else {
                                    LOG.debug("Path for watching not found [{0}], no longer watching.", _path);
                                }
                                close();
                                return;
                            }
                            if (_debug) {
                                LOG.error("Unknown error [{0}]", e, _debugStackTrace);
                            } else {
                                LOG.error("Unknown error", e);
                            }
                            throw new RuntimeException(e);
                        } catch (InterruptedException e) {
                            return;
                        }
                    }
                }
                _running.set(false);
            }
        });
        _watchThread.setName("Watch Children [" + _path + "][" + instance + "]");
        _watchThread.setDaemon(true);
        _watchThread.start();
        return this;
    }

    private void startDoubleCheckThread() {
        _doubleCheckThread = new Thread(new Runnable() {
            @Override
            public void run() {
                while (_running.get()) {
                    try {
                        synchronized (_running) {
                            _running.wait(_delay);
                        }
                        if (!_running.get()) {
                            return;
                        }
                        if (_zooKeeper.exists(_path, false) == null) {
                            LOG.debug("Path for watching not found [{0}], no longer double checking.", _path);
                            return;
                        }
                        List<String> children = _zooKeeper.getChildren(_path, false);
                        if (!isCorrect(children)) {
                            LOG.error("Double check triggered for [" + _path + "] [" + instance + "]");
                            synchronized (_lock) {
                                _lock.notify();
                            }
                        }
                    } catch (KeeperException e) {
                        if (!_running.get()) {
                            LOG.info("Error [{0}]", e.getMessage());
                            return;
                        }
                        if (e.code() == Code.SESSIONEXPIRED) {
                            LOG.warn("Session expired for [" + _path + "] [" + instance + "]");
                            return;
                        }
                        LOG.error("Unknown error", e);
                        throw new RuntimeException(e);
                    } catch (InterruptedException e) {
                        return;
                    }
                }
            }
        });
        _doubleCheckThread.setName("Poll Watch Children [" + _path + "][" + instance + "]");
        _doubleCheckThread.setDaemon(true);
        _doubleCheckThread.start();
    }

    protected boolean isCorrect(List<String> children) {
        if (children == null && _children == null) {
            return true;
        }
        if (children == null || _children == null) {
            return false;
        }
        return children.equals(_children);
    }

    public void close() {
        if (_running.get()) {
            LOG.warn("Closing [{0}]", instance);
            _running.set(false);
            if (_doubleCheckThread != null) {
                _doubleCheckThread.interrupt();
            }
            if (_watchThread != null) {
                _watchThread.interrupt();
            }
        }
    }
}