/*
* Copyright 2011 The Netty Project
*
* The Netty Project 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.jboss.netty.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.Executors;
import java.util.concurrent.ThreadFactory;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicBoolean;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.concurrent.locks.ReadWriteLock;
import java.util.concurrent.locks.ReentrantReadWriteLock;
import org.jboss.netty.channel.ChannelPipelineFactory;
import org.jboss.netty.logging.InternalLogger;
import org.jboss.netty.logging.InternalLoggerFactory;
import org.jboss.netty.util.internal.ConcurrentIdentityHashMap;
import org.jboss.netty.util.internal.ReusableIterator;
import org.jboss.netty.util.internal.SharedResourceMisuseDetector;
/**
* A {@link Timer} optimized for approximated I/O timeout scheduling.
*
* <h3>Tick Duration</h3>
*
* As described with 'approximated', this timer does not execute the scheduled
* {@link TimerTask} on time. {@link HashedWheelTimer}, on every tick, will
* check if there are any {@link TimerTask}s behind the schedule and execute
* them.
* <p>
* You can increase or decrease the accuracy of the execution timing by
* specifying smaller or larger tick duration in the constructor. In most
* network applications, I/O timeout does not need to be accurate. Therefore,
* the default tick duration is 100 milliseconds and you will not need to try
* different configurations in most cases.
*
* <h3>Ticks per Wheel (Wheel Size)</h3>
*
* {@link HashedWheelTimer} maintains a data structure called 'wheel'.
* To put simply, a wheel is a hash table of {@link TimerTask}s whose hash
* function is 'dead line of the task'. The default number of ticks per wheel
* (i.e. the size of the wheel) is 512. You could specify a larger value
* if you are going to schedule a lot of timeouts.
*
* <h3>Do not create many instances.</h3>
*
* {@link HashedWheelTimer} creates a new thread whenever it is instantiated and
* started. Therefore, you should make sure to create only one instance and
* share it across your application. One of the common mistakes, that makes
* your application unresponsive, is to create a new instance in
* {@link ChannelPipelineFactory}, which results in the creation of a new thread
* for every connection.
*
* <h3>Implementation Details</h3>
*
* {@link HashedWheelTimer} is based on
* <a href="http://cseweb.ucsd.edu/users/varghese/">George Varghese</a> and
* Tony Lauck's paper,
* <a href="http://cseweb.ucsd.edu/users/varghese/PAPERS/twheel.ps.Z">'Hashed
* and Hierarchical Timing Wheels: data structures to efficiently implement a
* timer facility'</a>. More comprehensive slides are located
* <a href="http://www.cse.wustl.edu/~cdgill/courses/cs6874/TimingWheels.ppt">here</a>.
*/
public class HashedWheelTimer implements Timer {
static final InternalLogger logger =
InternalLoggerFactory.getInstance(HashedWheelTimer.class);
private static final AtomicInteger id = new AtomicInteger();
private static final SharedResourceMisuseDetector misuseDetector =
new SharedResourceMisuseDetector(HashedWheelTimer.class);
private final Worker worker = new Worker();
final Thread workerThread;
final AtomicBoolean shutdown = new AtomicBoolean();
private final long roundDuration;
final long tickDuration;
final Set<HashedWheelTimeout>[] wheel;
final ReusableIterator<HashedWheelTimeout>[] iterators;
final int mask;
final ReadWriteLock lock = new ReentrantReadWriteLock();
volatile int wheelCursor;
/**
* Creates a new timer with the default thread factory
* ({@link Executors#defaultThreadFactory()}), default tick duration, and
* default number of ticks per wheel.
*/
public HashedWheelTimer() {
this(Executors.defaultThreadFactory());
}
/**
* Creates a new timer with the default thread factory
* ({@link Executors#defaultThreadFactory()}) and default number of ticks
* per wheel.
*
* @param tickDuration the duration between tick
* @param unit the time unit of the {@code tickDuration}
*/
public HashedWheelTimer(long tickDuration, TimeUnit unit) {
this(Executors.defaultThreadFactory(), tickDuration, unit);
}
/**
* Creates a new timer with the default thread factory
* ({@link Executors#defaultThreadFactory()}).
*
* @param tickDuration the duration between tick
* @param unit the time unit of the {@code tickDuration}
* @param ticksPerWheel the size of the wheel
*/
public HashedWheelTimer(long tickDuration, TimeUnit unit, int ticksPerWheel) {
this(Executors.defaultThreadFactory(), tickDuration, unit, ticksPerWheel);
}
/**
* Creates a new timer with the default tick duration and default number of
* ticks per wheel.
*
* @param threadFactory a {@link ThreadFactory} that creates a
* background {@link Thread} which is dedicated to
* {@link TimerTask} execution.
*/
public HashedWheelTimer(ThreadFactory threadFactory) {
this(threadFactory, 100, TimeUnit.MILLISECONDS);
}
/**
* Creates a new timer with the default number of ticks per wheel.
*
* @param threadFactory a {@link ThreadFactory} that creates a
* background {@link Thread} which is dedicated to
* {@link TimerTask} execution.
* @param tickDuration the duration between tick
* @param unit the time unit of the {@code tickDuration}
*/
public HashedWheelTimer(
ThreadFactory threadFactory, long tickDuration, TimeUnit unit) {
this(threadFactory, tickDuration, unit, 512);
}
/**
* Creates a new timer.
*
* @param threadFactory a {@link ThreadFactory} that creates a
* background {@link Thread} which is dedicated to
* {@link TimerTask} execution.
* @param tickDuration the duration between tick
* @param unit the time unit of the {@code tickDuration}
* @param ticksPerWheel the size of the wheel
*/
public HashedWheelTimer(
ThreadFactory threadFactory,
long tickDuration, TimeUnit unit, int ticksPerWheel) {
if (threadFactory == null) {
throw new NullPointerException("threadFactory");
}
if (unit == null) {
throw new NullPointerException("unit");
}
if (tickDuration <= 0) {
throw new IllegalArgumentException(
"tickDuration must be greater than 0: " + tickDuration);
}
if (ticksPerWheel <= 0) {
throw new IllegalArgumentException(
"ticksPerWheel must be greater than 0: " + ticksPerWheel);
}
// Normalize ticksPerWheel to power of two and initialize the wheel.
wheel = createWheel(ticksPerWheel);
iterators = createIterators(wheel);
mask = wheel.length - 1;
// Convert tickDuration to milliseconds.
this.tickDuration = tickDuration = unit.toMillis(tickDuration);
// Prevent overflow.
if (tickDuration == Long.MAX_VALUE ||
tickDuration >= Long.MAX_VALUE / wheel.length) {
throw new IllegalArgumentException(
"tickDuration is too long: " +
tickDuration + ' ' + unit);
}
roundDuration = tickDuration * wheel.length;
workerThread = threadFactory.newThread(new ThreadRenamingRunnable(
worker, "Hashed wheel timer #" + id.incrementAndGet()));
// Misuse check
misuseDetector.increase();
}
@SuppressWarnings("unchecked")
private static Set<HashedWheelTimeout>[] createWheel(int ticksPerWheel) {
if (ticksPerWheel <= 0) {
throw new IllegalArgumentException(
"ticksPerWheel must be greater than 0: " + ticksPerWheel);
}
if (ticksPerWheel > 1073741824) {
throw new IllegalArgumentException(
"ticksPerWheel may not be greater than 2^30: " + ticksPerWheel);
}
ticksPerWheel = normalizeTicksPerWheel(ticksPerWheel);
Set<HashedWheelTimeout>[] wheel = new Set[ticksPerWheel];
for (int i = 0; i < wheel.length; i ++) {
wheel[i] = new MapBackedSet<HashedWheelTimeout>(
new ConcurrentIdentityHashMap<HashedWheelTimeout, Boolean>(16, 0.95f, 4));
}
return wheel;
}
@SuppressWarnings("unchecked")
private static ReusableIterator<HashedWheelTimeout>[] createIterators(Set<HashedWheelTimeout>[] wheel) {
ReusableIterator<HashedWheelTimeout>[] iterators = new ReusableIterator[wheel.length];
for (int i = 0; i < wheel.length; i ++) {
iterators[i] = (ReusableIterator<HashedWheelTimeout>) wheel[i].iterator();
}
return iterators;
}
private static int normalizeTicksPerWheel(int ticksPerWheel) {
int normalizedTicksPerWheel = 1;
while (normalizedTicksPerWheel < ticksPerWheel) {
normalizedTicksPerWheel <<= 1;
}
return normalizedTicksPerWheel;
}
/**
* Starts the background thread explicitly. The background thread will
* start automatically on demand even if you did not call this method.
*
* @throws IllegalStateException if this timer has been
* {@linkplain #stop() stopped} already
*/
public synchronized void start() {
if (shutdown.get()) {
throw new IllegalStateException("cannot be started once stopped");
}
if (!workerThread.isAlive()) {
workerThread.start();
}
}
public synchronized Set<Timeout> stop() {
if (Thread.currentThread() == workerThread) {
throw new IllegalStateException(
HashedWheelTimer.class.getSimpleName() +
".stop() cannot be called from " +
TimerTask.class.getSimpleName());
}
if (!shutdown.compareAndSet(false, true)) {
return Collections.emptySet();
}
boolean interrupted = false;
while (workerThread.isAlive()) {
workerThread.interrupt();
try {
workerThread.join(100);
} catch (InterruptedException e) {
interrupted = true;
}
}
if (interrupted) {
Thread.currentThread().interrupt();
}
misuseDetector.decrease();
Set<Timeout> unprocessedTimeouts = new HashSet<Timeout>();
for (Set<HashedWheelTimeout> bucket: wheel) {
unprocessedTimeouts.addAll(bucket);
bucket.clear();
}
return Collections.unmodifiableSet(unprocessedTimeouts);
}
public Timeout newTimeout(TimerTask task, long delay, TimeUnit unit) {
final long currentTime = System.currentTimeMillis();
if (task == null) {
throw new NullPointerException("task");
}
if (unit == null) {
throw new NullPointerException("unit");
}
if (!workerThread.isAlive()) {
start();
}
delay = unit.toMillis(delay);
HashedWheelTimeout timeout = new HashedWheelTimeout(task, currentTime + delay);
scheduleTimeout(timeout, delay);
return timeout;
}
void scheduleTimeout(HashedWheelTimeout timeout, long delay) {
// delay must be equal to or greater than tickDuration so that the
// worker thread never misses the timeout.
if (delay < tickDuration) {
delay = tickDuration;
}
// Prepare the required parameters to schedule the timeout object.
final long lastRoundDelay = delay % roundDuration;
final long lastTickDelay = delay % tickDuration;
final long relativeIndex =
lastRoundDelay / tickDuration + (lastTickDelay != 0? 1 : 0);
final long remainingRounds =
delay / roundDuration - (delay % roundDuration == 0? 1 : 0);
// Add the timeout to the wheel.
lock.readLock().lock();
try {
int stopIndex = (int) (wheelCursor + relativeIndex & mask);
timeout.stopIndex = stopIndex;
timeout.remainingRounds = remainingRounds;
wheel[stopIndex].add(timeout);
} finally {
lock.readLock().unlock();
}
}
private final class Worker implements Runnable {
private long startTime;
private long tick;
Worker() {
super();
}
public void run() {
List<HashedWheelTimeout> expiredTimeouts =
new ArrayList<HashedWheelTimeout>();
startTime = System.currentTimeMillis();
tick = 1;
while (!shutdown.get()) {
final long deadline = waitForNextTick();
if (deadline > 0) {
fetchExpiredTimeouts(expiredTimeouts, deadline);
notifyExpiredTimeouts(expiredTimeouts);
}
}
}
private void fetchExpiredTimeouts(
List<HashedWheelTimeout> expiredTimeouts, long deadline) {
// Find the expired timeouts and decrease the round counter
// if necessary. Note that we don't send the notification
// immediately to make sure the listeners are called without
// an exclusive lock.
lock.writeLock().lock();
try {
int newWheelCursor = wheelCursor = wheelCursor + 1 & mask;
ReusableIterator<HashedWheelTimeout> i = iterators[newWheelCursor];
fetchExpiredTimeouts(expiredTimeouts, i, deadline);
} finally {
lock.writeLock().unlock();
}
}
private void fetchExpiredTimeouts(
List<HashedWheelTimeout> expiredTimeouts,
ReusableIterator<HashedWheelTimeout> i, long deadline) {
List<HashedWheelTimeout> slipped = null;
i.rewind();
while (i.hasNext()) {
HashedWheelTimeout timeout = i.next();
if (timeout.remainingRounds <= 0) {
i.remove();
if (timeout.deadline <= deadline) {
expiredTimeouts.add(timeout);
} else {
// Handle the case where the timeout is put into a wrong
// place, usually one tick earlier. For now, just add
// it to a temporary list - we will reschedule it in a
// separate loop.
if (slipped == null) {
slipped = new ArrayList<HashedWheelTimer.HashedWheelTimeout>();
}
slipped.add(timeout);
}
} else {
timeout.remainingRounds --;
}
}
// Reschedule the slipped timeouts.
if (slipped != null) {
for (HashedWheelTimeout timeout: slipped) {
scheduleTimeout(timeout, timeout.deadline - deadline);
}
}
}
private void notifyExpiredTimeouts(
List<HashedWheelTimeout> expiredTimeouts) {
// Notify the expired timeouts.
for (int i = expiredTimeouts.size() - 1; i >= 0; i --) {
expiredTimeouts.get(i).expire();
}
// Clean up the temporary list.
expiredTimeouts.clear();
}
private long waitForNextTick() {
long deadline = startTime + tickDuration * tick;
for (;;) {
final long currentTime = System.currentTimeMillis();
final long sleepTime = tickDuration * tick - (currentTime - startTime);
if (sleepTime <= 0) {
break;
}
try {
Thread.sleep(sleepTime);
} catch (InterruptedException e) {
if (shutdown.get()) {
return -1;
}
}
}
// Increase the tick.
tick ++;
return deadline;
}
}
private final class HashedWheelTimeout implements Timeout {
private static final int ST_INIT = 0;
private static final int ST_CANCELLED = 1;
private static final int ST_EXPIRED = 2;
private final TimerTask task;
final long deadline;
volatile int stopIndex;
volatile long remainingRounds;
private final AtomicInteger state = new AtomicInteger(ST_INIT);
HashedWheelTimeout(TimerTask task, long deadline) {
this.task = task;
this.deadline = deadline;
}
public Timer getTimer() {
return HashedWheelTimer.this;
}
public TimerTask getTask() {
return task;
}
public void cancel() {
if (!state.compareAndSet(ST_INIT, ST_CANCELLED)) {
// TODO return false
return;
}
wheel[stopIndex].remove(this);
}
public boolean isCancelled() {
return state.get() == ST_CANCELLED;
}
public boolean isExpired() {
return state.get() != ST_INIT;
}
public void expire() {
if (!state.compareAndSet(ST_INIT, ST_EXPIRED)) {
return;
}
try {
task.run(this);
} catch (Throwable t) {
if (logger.isWarnEnabled()) {
logger.warn(
"An exception was thrown by " +
TimerTask.class.getSimpleName() + ".", t);
}
}
}
@Override
public String toString() {
long currentTime = System.currentTimeMillis();
long remaining = deadline - currentTime;
StringBuilder buf = new StringBuilder(192);
buf.append(getClass().getSimpleName());
buf.append('(');
buf.append("deadline: ");
if (remaining > 0) {
buf.append(remaining);
buf.append(" ms later, ");
} else if (remaining < 0) {
buf.append(-remaining);
buf.append(" ms ago, ");
} else {
buf.append("now, ");
}
if (isCancelled()) {
buf.append(", cancelled");
}
return buf.append(')').toString();
}
}
}