gobblin.util.filesystem.PathAlterationObserverScheduler.java Source code

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Here is the source code for gobblin.util.filesystem.PathAlterationObserverScheduler.java

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/*
 * 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 gobblin.util.filesystem;

import java.io.IOException;
import java.util.List;
import java.util.concurrent.CopyOnWriteArrayList;
import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.ScheduledFuture;
import java.util.concurrent.TimeUnit;

import org.apache.hadoop.fs.Path;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import com.google.common.base.Optional;

import gobblin.util.ExecutorsUtils;

/**
 * A runnable that spawns a monitoring thread triggering any
 * registered {@link PathAlterationObserver} at a specified interval.
 *
 * Based on {@link org.apache.commons.io.monitor.FileAlterationMonitor}, implemented monitoring
 * thread to periodically check the monitored file in thread pool.
 */

public final class PathAlterationObserverScheduler implements Runnable {
    private static final Logger LOGGER = LoggerFactory.getLogger(PathAlterationObserverScheduler.class);
    private final long interval;
    private volatile boolean running = false;
    private final ScheduledExecutorService executor = Executors.newScheduledThreadPool(1,
            ExecutorsUtils.newDaemonThreadFactory(Optional.of(LOGGER), Optional.of("newDaemonThreadFactory")));
    private ScheduledFuture<?> executionResult;
    private final List<PathAlterationObserver> observers = new CopyOnWriteArrayList<PathAlterationObserver>();

    // Parameter for the running the Monitor periodically.
    private int initialDelay = 0;

    public PathAlterationObserverScheduler() {
        this(3000);
    }

    public PathAlterationObserverScheduler(final long interval) {
        this.interval = interval;
    }

    /**
     * Add a file system observer to this monitor.
     *
     * @param observer The file system observer to add
     */
    public void addObserver(final PathAlterationObserver observer) {
        if (observer != null) {
            observers.add(observer);
        }
    }

    /**
     * Remove a file system observer from this monitor.
     *
     * @param observer The file system observer to remove
     */
    public void removeObserver(final PathAlterationObserver observer) {
        if (observer != null) {
            while (observers.remove(observer)) {
            }
        }
    }

    /**
     * Returns the set of {@link PathAlterationObserver} registered with
     * this monitor.
     *
     * @return The set of {@link PathAlterationObserver}
     */
    public Iterable<PathAlterationObserver> getObservers() {
        return observers;
    }

    /**
     * Start monitoring.
     * @throws IOException if an error occurs initializing the observer
     */
    public synchronized void start() throws IOException {
        if (running) {
            throw new IllegalStateException("Monitor is already running");
        }
        for (final PathAlterationObserver observer : observers) {
            observer.initialize();
        }

        if (interval > 0) {
            running = true;
            this.executionResult = executor.scheduleWithFixedDelay(this, initialDelay, interval,
                    TimeUnit.MILLISECONDS);
        } else {
            LOGGER.info("Not starting due to non-positive scheduling interval:" + interval);
        }
    }

    /**
     * Stop monitoring
     *
     * @throws Exception if an error occurs initializing the observer
     */
    public synchronized void stop() throws IOException, InterruptedException {
        stop(interval);
    }

    /**
     * Stop monitoring
     *
     * @param stopInterval the amount of time in milliseconds to wait for the thread to finish.
     * A value of zero will wait until the thread is finished (see {@link Thread#join(long)}).
     * @throws IOException if an error occurs initializing the observer
     * @since 2.1
     */
    public synchronized void stop(final long stopInterval) throws IOException, InterruptedException {
        if (!running) {
            LOGGER.warn("Already stopped");
            return;
        }
        running = false;

        for (final PathAlterationObserver observer : observers) {
            observer.destroy();
        }

        executionResult.cancel(true);
        executor.shutdown();
        if (!executor.awaitTermination(stopInterval, TimeUnit.MILLISECONDS)) {
            throw new RuntimeException("Did not shutdown in the timeout period");
        }
    }

    @Override
    public void run() {
        if (!running) {
            return;
        }
        for (final PathAlterationObserver observer : observers) {
            try {
                observer.checkAndNotify();
            } catch (IOException ioe) {
                LOGGER.error("Path alteration detector error.", ioe);
            }
        }
    }

    /**
     * Create and attach {@link PathAlterationObserverScheduler}s for the given
     * root directory and any nested subdirectories under the root directory to the given
     * {@link PathAlterationObserverScheduler}.
     * @param detector  a {@link PathAlterationObserverScheduler}
     * @param listener a {@link gobblin.util.filesystem.PathAlterationListener}
     * @param observerOptional Optional observer object. For testing routine, this has been initialized by user.
     *                         But for general usage, the observer object is created inside this method.
     * @param rootDirPath root directory
     * @throws IOException
     */
    public void addPathAlterationObserver(PathAlterationListener listener,
            Optional<PathAlterationObserver> observerOptional, Path rootDirPath) throws IOException {
        PathAlterationObserver observer = observerOptional.or(new PathAlterationObserver(rootDirPath));
        observer.addListener(listener);
        addObserver(observer);
    }

}