/**
* 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.hadoop.util;
import com.google.common.util.concurrent.ThreadFactoryBuilder;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.HashSet;
import java.util.List;
import java.util.Set;
import java.util.concurrent.Executors;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Future;
import java.util.concurrent.TimeoutException;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicBoolean;
/**
* The <code>ShutdownHookManager</code> enables running shutdownHook
* in a deterministic order, higher priority first.
* <p/>
* The JVM runs ShutdownHooks in a non-deterministic order or in parallel.
* This class registers a single JVM shutdownHook and run all the
* shutdownHooks registered to it (to this class) in order based on their
* priority.
*/
public class ShutdownHookManager {
private static final ShutdownHookManager MGR = new ShutdownHookManager();
private static final Log LOG = LogFactory.getLog(ShutdownHookManager.class);
private static final long TIMEOUT_DEFAULT = 10;
private static final TimeUnit TIME_UNIT_DEFAULT = TimeUnit.SECONDS;
private static final ExecutorService EXECUTOR =
Executors.newSingleThreadExecutor(new ThreadFactoryBuilder()
.setDaemon(true).build());
static {
try {
Runtime.getRuntime().addShutdownHook(
new Thread() {
@Override
public void run() {
MGR.shutdownInProgress.set(true);
for (HookEntry entry: MGR.getShutdownHooksInOrder()) {
Future<?> future = EXECUTOR.submit(entry.getHook());
try {
future.get(entry.getTimeout(), entry.getTimeUnit());
} catch (TimeoutException ex) {
future.cancel(true);
LOG.warn("ShutdownHook '" + entry.getHook().getClass().
getSimpleName() + "' timeout, " + ex.toString(), ex);
} catch (Throwable ex) {
LOG.warn("ShutdownHook '" + entry.getHook().getClass().
getSimpleName() + "' failed, " + ex.toString(), ex);
}
}
try {
EXECUTOR.shutdown();
if (!EXECUTOR.awaitTermination(TIMEOUT_DEFAULT,
TIME_UNIT_DEFAULT)) {
LOG.error("ShutdownHookManger shutdown forcefully.");
EXECUTOR.shutdownNow();
}
LOG.debug("ShutdownHookManger complete shutdown.");
} catch (InterruptedException ex) {
LOG.error("ShutdownHookManger interrupted while waiting for " +
"termination.", ex);
EXECUTOR.shutdownNow();
Thread.currentThread().interrupt();
}
}
}
);
} catch (IllegalStateException ex) {
// JVM is being shut down. Ignore
LOG.warn("Failed to add the ShutdownHook", ex);
}
}
/**
* Return <code>ShutdownHookManager</code> singleton.
*
* @return <code>ShutdownHookManager</code> singleton.
*/
public static ShutdownHookManager get() {
return MGR;
}
/**
* Private structure to store ShutdownHook, its priority and timeout
* settings.
*/
static class HookEntry {
private final Runnable hook;
private final int priority;
private final long timeout;
private final TimeUnit unit;
HookEntry(Runnable hook, int priority) {
this(hook, priority, TIMEOUT_DEFAULT, TIME_UNIT_DEFAULT);
}
HookEntry(Runnable hook, int priority, long timeout, TimeUnit unit) {
this.hook = hook;
this.priority = priority;
this.timeout = timeout;
this.unit = unit;
}
@Override
public int hashCode() {
return hook.hashCode();
}
@Override
public boolean equals(Object obj) {
boolean eq = false;
if (obj != null) {
if (obj instanceof HookEntry) {
eq = (hook == ((HookEntry)obj).hook);
}
}
return eq;
}
Runnable getHook() {
return hook;
}
int getPriority() {
return priority;
}
long getTimeout() {
return timeout;
}
TimeUnit getTimeUnit() {
return unit;
}
}
private final Set<HookEntry> hooks =
Collections.synchronizedSet(new HashSet<HookEntry>());
private AtomicBoolean shutdownInProgress = new AtomicBoolean(false);
//private to constructor to ensure singularity
private ShutdownHookManager() {
}
/**
* Returns the list of shutdownHooks in order of execution,
* Highest priority first.
*
* @return the list of shutdownHooks in order of execution.
*/
List<HookEntry> getShutdownHooksInOrder() {
List<HookEntry> list;
synchronized (MGR.hooks) {
list = new ArrayList<HookEntry>(MGR.hooks);
}
Collections.sort(list, new Comparator<HookEntry>() {
//reversing comparison so highest priority hooks are first
@Override
public int compare(HookEntry o1, HookEntry o2) {
return o2.priority - o1.priority;
}
});
return list;
}
/**
* Adds a shutdownHook with a priority, the higher the priority
* the earlier will run. ShutdownHooks with same priority run
* in a non-deterministic order.
*
* @param shutdownHook shutdownHook <code>Runnable</code>
* @param priority priority of the shutdownHook.
*/
public void addShutdownHook(Runnable shutdownHook, int priority) {
if (shutdownHook == null) {
throw new IllegalArgumentException("shutdownHook cannot be NULL");
}
if (shutdownInProgress.get()) {
throw new IllegalStateException("Shutdown in progress, cannot add a " +
"shutdownHook");
}
hooks.add(new HookEntry(shutdownHook, priority));
}
/**
*
* Adds a shutdownHook with a priority and timeout the higher the priority
* the earlier will run. ShutdownHooks with same priority run
* in a non-deterministic order. The shutdown hook will be terminated if it
* has not been finished in the specified period of time.
*
* @param shutdownHook shutdownHook <code>Runnable</code>
* @param priority priority of the shutdownHook
* @param timeout timeout of the shutdownHook
* @param unit unit of the timeout <code>TimeUnit</code>
*/
public void addShutdownHook(Runnable shutdownHook, int priority, long timeout,
TimeUnit unit) {
if (shutdownHook == null) {
throw new IllegalArgumentException("shutdownHook cannot be NULL");
}
if (shutdownInProgress.get()) {
throw new IllegalStateException("Shutdown in progress, cannot add a " +
"shutdownHook");
}
hooks.add(new HookEntry(shutdownHook, priority, timeout, unit));
}
/**
* Removes a shutdownHook.
*
* @param shutdownHook shutdownHook to remove.
* @return TRUE if the shutdownHook was registered and removed,
* FALSE otherwise.
*/
public boolean removeShutdownHook(Runnable shutdownHook) {
if (shutdownInProgress.get()) {
throw new IllegalStateException("Shutdown in progress, cannot remove a " +
"shutdownHook");
}
return hooks.remove(new HookEntry(shutdownHook, 0));
}
/**
* Indicates if a shutdownHook is registered or not.
*
* @param shutdownHook shutdownHook to check if registered.
* @return TRUE/FALSE depending if the shutdownHook is is registered.
*/
public boolean hasShutdownHook(Runnable shutdownHook) {
return hooks.contains(new HookEntry(shutdownHook, 0));
}
/**
* Indicates if shutdown is in progress or not.
*
* @return TRUE if the shutdown is in progress, otherwise FALSE.
*/
public boolean isShutdownInProgress() {
return shutdownInProgress.get();
}
/**
* clear all registered shutdownHooks.
*/
public void clearShutdownHooks() {
hooks.clear();
}
}