/*******************************************************************************
* Copyright 2013 André Rouél
*
* Licensed 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 net.sf.uadetector.internal.util;
import java.util.ArrayList;
import java.util.Collections;
import java.util.HashSet;
import java.util.List;
import java.util.Set;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.TimeUnit;
import javax.annotation.Nonnegative;
import javax.annotation.Nonnull;
import net.sf.qualitycheck.Check;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
/**
* This utility is intended to provide predefined {@link ExecutorService}s which runs in background and can be easily
* shut-downed within {@link #shutdownAll()} if necessary.
*
* @author André Rouél
*/
public final class ExecutorServices {
/**
* This synchronized {@link Set} is a registry of all distributed background executors by this utility.
* <p>
* The containing {@link ExecutorService}s will be used to run a concrete update of <i>UAS data</i> instantly in
* background.
*/
private static final Set<ExecutorService> BACKGROUND_EXECUTORS = Collections.synchronizedSet(new HashSet<ExecutorService>(3));
/**
* Default name of a thread which will be used to run a concrete update within a background executor
*/
private static final String DEFAULT_BACKGROUND_EXECUTOR_NAME = "update-operation";
/**
* Default name of a thread which will be created within a scheduler
*/
private static final String DEFAULT_SCHEDULER_NAME = "update-scheduler";
/**
* Corresponding logger for this class
*/
private static final Logger LOG = LoggerFactory.getLogger(ExecutorServices.class);
/**
* This synchronized {@link Set} is a registry of all distributed schedulers by this utility.
* <p>
* The containing {@link ScheduledExecutorService}s will be used to schedule commands which updates the <i>UAS
* data</i> in defined intervals.
*/
private static final Set<ScheduledExecutorService> SCHEDULERS = Collections.synchronizedSet(new HashSet<ScheduledExecutorService>(3));
/**
* Timeout (in seconds) to shutdown all available executors at the latest
*/
public static final long SHUTDOWN_DURATION = 5;
/**
* Creates a single-threaded executor that is registered by this class in order to shut it down later (when it
* becomes necessary).
*
* @return a new background executor
*/
public static ExecutorService createBackgroundExecutor() {
final ExecutorService executor = Executors.newSingleThreadExecutor(new DaemonThreadFactory(DEFAULT_BACKGROUND_EXECUTOR_NAME));
BACKGROUND_EXECUTORS.add(executor);
return executor;
}
/**
* Creates a single-threaded scheduler that is registered by this class in order to shut it down later (when it
* becomes necessary).
*
* @return a new scheduler
*/
public static ScheduledExecutorService createScheduler() {
final ScheduledExecutorService scheduler = Executors.newScheduledThreadPool(1, new DaemonThreadFactory(DEFAULT_SCHEDULER_NAME));
SCHEDULERS.add(scheduler);
return scheduler;
}
/**
* Shutdowns the given {@code ExecutorService} as soon as possible, but not later than the specified default time
* (which is {@value #SHUTDOWN_DURATION} seconds).
*
* @param executorService
* executor to stop
*/
public static void shutdown(@Nonnull final ExecutorService executorService) {
Check.notNull(executorService, "executorService");
shutdown(executorService, SHUTDOWN_DURATION, TimeUnit.SECONDS);
}
/**
* Shutdowns the given {@code ExecutorService} as soon as possible, but not later than the specified time.
*
* @param executorService
* executor to stop
* @param duration
* duration as a numerical value
* @param unit
* duration unit
*/
public static void shutdown(@Nonnull final ExecutorService executorService, @Nonnegative final long duration,
@Nonnull final TimeUnit unit) {
Check.notNull(executorService, "executorService");
Check.notNull(duration, "duration");
Check.notNull(unit, "unit");
executorService.shutdown();
try {
if (!executorService.awaitTermination(duration, unit)) {
LOG.info(String.format("Executor did not terminate in %s %s.", duration, unit.name().toLowerCase()));
final List<Runnable> droppedTasks = executorService.shutdownNow();
LOG.info("Executor was abruptly shut down. " + droppedTasks.size() + " tasks will not be executed.");
}
unregisterIfPossible(executorService);
} catch (final InterruptedException e) {
LOG.warn("Executor termination failed: " + e.getLocalizedMessage(), e);
}
}
/**
* Shuts down all registered scheduler and background workers as soon as possible, but at the latest in specified
* {@link #SHUTDOWN_DURATION} seconds.
*/
public static void shutdownAll() {
for (final ExecutorService executor : new ArrayList<ExecutorService>(BACKGROUND_EXECUTORS)) {
shutdown(executor);
BACKGROUND_EXECUTORS.remove(executor);
}
for (final ScheduledExecutorService scheduler : new ArrayList<ScheduledExecutorService>(SCHEDULERS)) {
shutdown(scheduler);
SCHEDULERS.remove(scheduler);
}
}
/**
* Unregisters the given {@code ExecutorService} if it is an instance of {@code ScheduledExecutorService} from the
* list of registered schedulers.
*
* @param executorService
* a possible scheduler
*/
private static void unregisterIfPossible(final ExecutorService executorService) {
if (executorService instanceof ScheduledExecutorService) {
SCHEDULERS.remove(executorService);
} else {
BACKGROUND_EXECUTORS.remove(executorService);
}
}
/**
* <strong>Attention:</strong> This class is not intended to create objects from it.
*/
private ExecutorServices() {
// This class is not intended to create objects from it.
}
}