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 {@link ReloadingController} and a period. After
033 * calling the {@code start()} method a periodic task is started which calls
034 * {@link ReloadingController#checkForReloading(Object)} on the associated reloading controller. This way changes on a
035 * configuration source can be detected without client code having to poll actively. The {@code ReloadingController}
036 * will perform its checks and generates events if it detects the need for a reloading operation.
037 * </p>
038 * <p>
039 * Triggering of the controller can be disabled by calling the {@code stop()} method and later be resumed by calling
040 * {@code start()} again. When the trigger is no more needed its {@code shutdown()} method should be called.
041 * </p>
042 * <p>
043 * When creating an instance a {@code ScheduledExecutorService} can be provided which is then used by the object.
044 * Otherwise, a default executor service is created and used. When shutting down this object it can be specified whether
045 * the {@code ScheduledExecutorService} should be shut down, too.
046 * </p>
047 *
048 * @since 2.0
049 * @see ReloadingController
050 */
051public class PeriodicReloadingTrigger {
052    /** The executor service used by this trigger. */
053    private final ScheduledExecutorService executorService;
054
055    /** The associated reloading controller. */
056    private final ReloadingController controller;
057
058    /** The parameter to be passed to the controller. */
059    private final Object controllerParam;
060
061    /** The period. */
062    private final long period;
063
064    /** The time unit. */
065    private final TimeUnit timeUnit;
066
067    /** Stores the future object for the current trigger task. */
068    private ScheduledFuture<?> triggerTask;
069
070    /**
071     * Creates a new instance of {@code PeriodicReloadingTrigger} and sets all parameters.
072     *
073     * @param ctrl the {@code ReloadingController} (must not be <b>null</b>)
074     * @param ctrlParam the optional parameter to be passed to the controller when doing reloading checks
075     * @param triggerPeriod the period in which the controller is triggered
076     * @param unit the time unit for the period
077     * @param exec the executor service to use (can be <b>null</b>, then a default executor service is created
078     * @throws IllegalArgumentException if a required argument is missing
079     */
080    public PeriodicReloadingTrigger(final ReloadingController ctrl, final Object ctrlParam, final long triggerPeriod, final TimeUnit unit,
081        final ScheduledExecutorService exec) {
082        if (ctrl == null) {
083            throw new IllegalArgumentException("ReloadingController must not be null!");
084        }
085
086        controller = ctrl;
087        controllerParam = ctrlParam;
088        period = triggerPeriod;
089        timeUnit = unit;
090        executorService = exec != null ? exec : createDefaultExecutorService();
091    }
092
093    /**
094     * Creates a new instance of {@code PeriodicReloadingTrigger} with a default executor service.
095     *
096     * @param ctrl the {@code ReloadingController} (must not be <b>null</b>)
097     * @param ctrlParam the optional parameter to be passed to the controller when doing reloading checks
098     * @param triggerPeriod the period in which the controller is triggered
099     * @param unit the time unit for the period
100     * @throws IllegalArgumentException if a required argument is missing
101     */
102    public PeriodicReloadingTrigger(final ReloadingController ctrl, final Object ctrlParam, final long triggerPeriod, final TimeUnit unit) {
103        this(ctrl, ctrlParam, triggerPeriod, unit, null);
104    }
105
106    /**
107     * Starts this trigger. The associated {@code ReloadingController} will be triggered according to the specified period.
108     * The first triggering happens after a period. If this trigger is already started, this invocation has no effect.
109     */
110    public synchronized void start() {
111        if (!isRunning()) {
112            triggerTask = getExecutorService().scheduleAtFixedRate(createTriggerTaskCommand(), period, period, timeUnit);
113        }
114    }
115
116    /**
117     * Stops this trigger. The associated {@code ReloadingController} is no more triggered. If this trigger is already
118     * stopped, this invocation has no effect.
119     */
120    public synchronized void stop() {
121        if (isRunning()) {
122            triggerTask.cancel(false);
123            triggerTask = null;
124        }
125    }
126
127    /**
128     * Returns a flag whether this trigger is currently active.
129     *
130     * @return a flag whether this trigger is running
131     */
132    public synchronized boolean isRunning() {
133        return triggerTask != null;
134    }
135
136    /**
137     * Shuts down this trigger and optionally shuts down the {@code ScheduledExecutorService} used by this object. This
138     * method should be called if this trigger is no more needed. It ensures that the trigger is stopped. If the parameter
139     * is <b>true</b>, the executor service is also shut down. This should be done if this trigger is the only user of this
140     * executor service.
141     *
142     * @param shutdownExecutor a flag whether the associated {@code ScheduledExecutorService} is to be shut down
143     */
144    public void shutdown(final boolean shutdownExecutor) {
145        stop();
146        if (shutdownExecutor) {
147            getExecutorService().shutdown();
148        }
149    }
150
151    /**
152     * Shuts down this trigger and its {@code ScheduledExecutorService}. This is a shortcut for {@code shutdown(true)}.
153     *
154     * @see #shutdown(boolean)
155     */
156    public void shutdown() {
157        shutdown(true);
158    }
159
160    /**
161     * Gets the {@code ScheduledExecutorService} used by this object.
162     *
163     * @return the associated {@code ScheduledExecutorService}
164     */
165    ScheduledExecutorService getExecutorService() {
166        return executorService;
167    }
168
169    /**
170     * Creates the task which triggers the reloading controller.
171     *
172     * @return the newly created trigger task
173     */
174    private Runnable createTriggerTaskCommand() {
175        return () -> controller.checkForReloading(controllerParam);
176    }
177
178    /**
179     * Creates a default executor service. This method is called if no executor has been passed to the constructor.
180     *
181     * @return the default executor service
182     */
183    private static ScheduledExecutorService createDefaultExecutorService() {
184        final ThreadFactory factory = new BasicThreadFactory.Builder().namingPattern("ReloadingTrigger-%s").daemon(true).build();
185        return Executors.newScheduledThreadPool(1, factory);
186    }
187}