PeriodicReloadingTrigger.java
/*
* 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.commons.configuration2.reloading;
import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.ScheduledFuture;
import java.util.concurrent.ThreadFactory;
import java.util.concurrent.TimeUnit;
import org.apache.commons.lang3.concurrent.BasicThreadFactory;
/**
* <p>
* A timer-based trigger for reloading checks.
* </p>
* <p>
* An instance of this class is constructed with a reference to a {@link ReloadingController} and a period. After
* calling the {@code start()} method a periodic task is started which calls
* {@link ReloadingController#checkForReloading(Object)} on the associated reloading controller. This way changes on a
* configuration source can be detected without client code having to poll actively. The {@code ReloadingController}
* will perform its checks and generates events if it detects the need for a reloading operation.
* </p>
* <p>
* Triggering of the controller can be disabled by calling the {@code stop()} method and later be resumed by calling
* {@code start()} again. When the trigger is no more needed its {@code shutdown()} method should be called.
* </p>
* <p>
* When creating an instance a {@code ScheduledExecutorService} can be provided which is then used by the object.
* Otherwise, a default executor service is created and used. When shutting down this object it can be specified whether
* the {@code ScheduledExecutorService} should be shut down, too.
* </p>
*
* @since 2.0
* @see ReloadingController
*/
public class PeriodicReloadingTrigger {
/**
* Creates a default executor service. This method is called if no executor has been passed to the constructor.
*
* @return the default executor service
*/
private static ScheduledExecutorService createDefaultExecutorService() {
final ThreadFactory factory = new BasicThreadFactory.Builder().namingPattern("ReloadingTrigger-%s").daemon(true).build();
return Executors.newScheduledThreadPool(1, factory);
}
/** The executor service used by this trigger. */
private final ScheduledExecutorService executorService;
/** The associated reloading controller. */
private final ReloadingController controller;
/** The parameter to be passed to the controller. */
private final Object controllerParam;
/** The period. */
private final long period;
/** The time unit. */
private final TimeUnit timeUnit;
/** Stores the future object for the current trigger task. */
private ScheduledFuture<?> triggerTask;
/**
* Creates a new instance of {@code PeriodicReloadingTrigger} with a default executor service.
*
* @param ctrl the {@code ReloadingController} (must not be <b>null</b>)
* @param ctrlParam the optional parameter to be passed to the controller when doing reloading checks
* @param triggerPeriod the period in which the controller is triggered
* @param unit the time unit for the period
* @throws IllegalArgumentException if a required argument is missing
*/
public PeriodicReloadingTrigger(final ReloadingController ctrl, final Object ctrlParam, final long triggerPeriod, final TimeUnit unit) {
this(ctrl, ctrlParam, triggerPeriod, unit, null);
}
/**
* Creates a new instance of {@code PeriodicReloadingTrigger} and sets all parameters.
*
* @param ctrl the {@code ReloadingController} (must not be <b>null</b>)
* @param ctrlParam the optional parameter to be passed to the controller when doing reloading checks
* @param triggerPeriod the period in which the controller is triggered
* @param unit the time unit for the period
* @param exec the executor service to use (can be <b>null</b>, then a default executor service is created
* @throws IllegalArgumentException if a required argument is missing
*/
public PeriodicReloadingTrigger(final ReloadingController ctrl, final Object ctrlParam, final long triggerPeriod, final TimeUnit unit,
final ScheduledExecutorService exec) {
if (ctrl == null) {
throw new IllegalArgumentException("ReloadingController must not be null!");
}
controller = ctrl;
controllerParam = ctrlParam;
period = triggerPeriod;
timeUnit = unit;
executorService = exec != null ? exec : createDefaultExecutorService();
}
/**
* Creates the task which triggers the reloading controller.
*
* @return the newly created trigger task
*/
private Runnable createTriggerTaskCommand() {
return () -> controller.checkForReloading(controllerParam);
}
/**
* Gets the {@code ScheduledExecutorService} used by this object.
*
* @return the associated {@code ScheduledExecutorService}
*/
ScheduledExecutorService getExecutorService() {
return executorService;
}
/**
* Returns a flag whether this trigger is currently active.
*
* @return a flag whether this trigger is running
*/
public synchronized boolean isRunning() {
return triggerTask != null;
}
/**
* Shuts down this trigger and its {@code ScheduledExecutorService}. This is a shortcut for {@code shutdown(true)}.
*
* @see #shutdown(boolean)
*/
public void shutdown() {
shutdown(true);
}
/**
* Shuts down this trigger and optionally shuts down the {@code ScheduledExecutorService} used by this object. This
* method should be called if this trigger is no more needed. It ensures that the trigger is stopped. If the parameter
* is <b>true</b>, the executor service is also shut down. This should be done if this trigger is the only user of this
* executor service.
*
* @param shutdownExecutor a flag whether the associated {@code ScheduledExecutorService} is to be shut down
*/
public void shutdown(final boolean shutdownExecutor) {
stop();
if (shutdownExecutor) {
getExecutorService().shutdown();
}
}
/**
* Starts this trigger. The associated {@code ReloadingController} will be triggered according to the specified period.
* The first triggering happens after a period. If this trigger is already started, this invocation has no effect.
*/
public synchronized void start() {
if (!isRunning()) {
triggerTask = getExecutorService().scheduleAtFixedRate(createTriggerTaskCommand(), period, period, timeUnit);
}
}
/**
* Stops this trigger. The associated {@code ReloadingController} is no more triggered. If this trigger is already
* stopped, this invocation has no effect.
*/
public synchronized void stop() {
if (isRunning()) {
triggerTask.cancel(false);
triggerTask = null;
}
}
}