001/*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements.  See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License.  You may obtain a copy of the License at
008 *
009 *     http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017package org.apache.commons.configuration2.reloading;
018
019import java.util.concurrent.Executors;
020import java.util.concurrent.ScheduledExecutorService;
021import java.util.concurrent.ScheduledFuture;
022import java.util.concurrent.ThreadFactory;
023import java.util.concurrent.TimeUnit;
024
025import org.apache.commons.lang3.concurrent.BasicThreadFactory;
026
027/**
028 * <p>
029 * A timer-based trigger for reloading checks.
030 * </p>
031 * <p>
032 * An instance of this class is constructed with a reference to a
033 * {@link ReloadingController} and a period. After calling the {@code start()}
034 * method a periodic task is started which calls
035 * {@link ReloadingController#checkForReloading(Object)} on the associated
036 * reloading controller. This way changes on a configuration source can be
037 * detected without client code having to poll actively. The
038 * {@code ReloadingController} will perform its checks and generates events if
039 * it detects the need for a reloading operation.
040 * </p>
041 * <p>
042 * Triggering of the controller can be disabled by calling the {@code stop()}
043 * method and later be resumed by calling {@code start()} again. When the
044 * trigger is no more needed its {@code shutdown()} method should be called.
045 * </p>
046 * <p>
047 * When creating an instance a {@code ScheduledExecutorService} can be provided
048 * which is then used by the object. Otherwise, a default executor service is
049 * created and used. When shutting down this object it can be specified whether
050 * the {@code ScheduledExecutorService} should be shut down, too.
051 * </p>
052 *
053 * @since 2.0
054 * @see ReloadingController
055 */
056public class PeriodicReloadingTrigger
057{
058    /** The executor service used by this trigger. */
059    private final ScheduledExecutorService executorService;
060
061    /** The associated reloading controller. */
062    private final ReloadingController controller;
063
064    /** The parameter to be passed to the controller. */
065    private final Object controllerParam;
066
067    /** The period. */
068    private final long period;
069
070    /** The time unit. */
071    private final TimeUnit timeUnit;
072
073    /** Stores the future object for the current trigger task. */
074    private ScheduledFuture<?> triggerTask;
075
076    /**
077     * Creates a new instance of {@code PeriodicReloadingTrigger} and sets all
078     * parameters.
079     *
080     * @param ctrl the {@code ReloadingController} (must not be <b>null</b>)
081     * @param ctrlParam the optional parameter to be passed to the controller
082     *        when doing reloading checks
083     * @param triggerPeriod the period in which the controller is triggered
084     * @param unit the time unit for the period
085     * @param exec the executor service to use (can be <b>null</b>, then a
086     *        default executor service is created
087     * @throws IllegalArgumentException if a required argument is missing
088     */
089    public PeriodicReloadingTrigger(final ReloadingController ctrl, final Object ctrlParam,
090            final long triggerPeriod, final TimeUnit unit, final ScheduledExecutorService exec)
091    {
092        if (ctrl == null)
093        {
094            throw new IllegalArgumentException(
095                    "ReloadingController must not be null!");
096        }
097
098        controller = ctrl;
099        controllerParam = ctrlParam;
100        period = triggerPeriod;
101        timeUnit = unit;
102        executorService =
103                exec != null ? exec : createDefaultExecutorService();
104    }
105
106    /**
107     * Creates a new instance of {@code PeriodicReloadingTrigger} with a default
108     * executor service.
109     *
110     * @param ctrl the {@code ReloadingController} (must not be <b>null</b>)
111     * @param ctrlParam the optional parameter to be passed to the controller
112     *        when doing reloading checks
113     * @param triggerPeriod the period in which the controller is triggered
114     * @param unit the time unit for the period
115     * @throws IllegalArgumentException if a required argument is missing
116     */
117    public PeriodicReloadingTrigger(final ReloadingController ctrl, final Object ctrlParam,
118            final long triggerPeriod, final TimeUnit unit)
119    {
120        this(ctrl, ctrlParam, triggerPeriod, unit, null);
121    }
122
123    /**
124     * Starts this trigger. The associated {@code ReloadingController} will be
125     * triggered according to the specified period. The first triggering happens
126     * after a period. If this trigger is already started, this invocation has
127     * no effect.
128     */
129    public synchronized void start()
130    {
131        if (!isRunning())
132        {
133            triggerTask =
134                    getExecutorService().scheduleAtFixedRate(
135                            createTriggerTaskCommand(), period, period,
136                            timeUnit);
137        }
138    }
139
140    /**
141     * Stops this trigger. The associated {@code ReloadingController} is no more
142     * triggered. If this trigger is already stopped, this invocation has no
143     * effect.
144     */
145    public synchronized void stop()
146    {
147        if (isRunning())
148        {
149            triggerTask.cancel(false);
150            triggerTask = null;
151        }
152    }
153
154    /**
155     * Returns a flag whether this trigger is currently active.
156     *
157     * @return a flag whether this trigger is running
158     */
159    public synchronized boolean isRunning()
160    {
161        return triggerTask != null;
162    }
163
164    /**
165     * Shuts down this trigger and optionally shuts down the
166     * {@code ScheduledExecutorService} used by this object. This method should
167     * be called if this trigger is no more needed. It ensures that the trigger
168     * is stopped. If the parameter is <b>true</b>, the executor service is also
169     * shut down. This should be done if this trigger is the only user of this
170     * executor service.
171     *
172     * @param shutdownExecutor a flag whether the associated
173     *        {@code ScheduledExecutorService} is to be shut down
174     */
175    public void shutdown(final boolean shutdownExecutor)
176    {
177        stop();
178        if (shutdownExecutor)
179        {
180            getExecutorService().shutdown();
181        }
182    }
183
184    /**
185     * Shuts down this trigger and its {@code ScheduledExecutorService}. This is
186     * a shortcut for {@code shutdown(true)}.
187     *
188     * @see #shutdown(boolean)
189     */
190    public void shutdown()
191    {
192        shutdown(true);
193    }
194
195    /**
196     * Returns the {@code ScheduledExecutorService} used by this object.
197     *
198     * @return the associated {@code ScheduledExecutorService}
199     */
200    ScheduledExecutorService getExecutorService()
201    {
202        return executorService;
203    }
204
205    /**
206     * Creates the task which triggers the reloading controller.
207     *
208     * @return the newly created trigger task
209     */
210    private Runnable createTriggerTaskCommand()
211    {
212        return () -> controller.checkForReloading(controllerParam);
213    }
214
215    /**
216     * Creates a default executor service. This method is called if no executor
217     * has been passed to the constructor.
218     *
219     * @return the default executor service
220     */
221    private static ScheduledExecutorService createDefaultExecutorService()
222    {
223        final ThreadFactory factory =
224                new BasicThreadFactory.Builder()
225                        .namingPattern("ReloadingTrigger-%s").daemon(true)
226                        .build();
227        return Executors.newScheduledThreadPool(1, factory);
228    }
229}