io.netty.util.HashedWheelTimer Maven / Gradle / Ivy
/*
* Copyright 2012 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 io.netty.util;
import io.netty.util.internal.PlatformDependent;
import io.netty.util.internal.logging.InternalLogger;
import io.netty.util.internal.logging.InternalLoggerFactory;
import java.util.ArrayList;
import java.util.Collections;
import java.util.HashSet;
import java.util.Iterator;
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.AtomicInteger;
import java.util.concurrent.locks.ReadWriteLock;
import java.util.concurrent.locks.ReentrantReadWriteLock;
/**
* A {@link Timer} optimized for approximated I/O timeout scheduling.
*
* Tick Duration
*
* 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.
*
* 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.
*
*
Ticks per Wheel (Wheel Size)
*
* {@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.
*
* Do not create many instances.
*
* {@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 for every connection.
*
* Implementation Details
*
* {@link HashedWheelTimer} is based on
* George Varghese and
* Tony Lauck's paper,
* 'Hashed
* and Hierarchical Timing Wheels: data structures to efficiently implement a
* timer facility'. More comprehensive slides are located
* here.
*/
public class HashedWheelTimer implements Timer {
static final InternalLogger logger =
InternalLoggerFactory.getInstance(HashedWheelTimer.class);
private static final ResourceLeakDetector leakDetector =
new ResourceLeakDetector(
HashedWheelTimer.class, 1, Runtime.getRuntime().availableProcessors() * 4);
private final ResourceLeak leak;
private final Worker worker = new Worker();
final Thread workerThread;
public static final int WORKER_STATE_INIT = 0;
public static final int WORKER_STATE_STARTED = 1;
public static final int WORKER_STATE_SHUTDOWN = 2;
final AtomicInteger workerState = new AtomicInteger(); // 0 - init, 1 - started, 2 - shut down
final long tickDuration;
final Set[] wheel;
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}
* @throws NullPointerException if {@code unit} is {@code null}
* @throws IllegalArgumentException if {@code tickDuration} is <= 0
*/
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
* @throws NullPointerException if {@code unit} is {@code null}
* @throws IllegalArgumentException if either of {@code tickDuration} and {@code ticksPerWheel} is <= 0
*/
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.
* @throws NullPointerException if {@code threadFactory} is {@code null}
*/
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}
* @throws NullPointerException if either of {@code threadFactory} and {@code unit} is {@code null}
* @throws IllegalArgumentException if {@code tickDuration} is <= 0
*/
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
* @throws NullPointerException if either of {@code threadFactory} and {@code unit} is {@code null}
* @throws IllegalArgumentException if either of {@code tickDuration} and {@code ticksPerWheel} is <= 0
*/
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);
mask = wheel.length - 1;
// Convert tickDuration to nanos.
this.tickDuration = unit.toNanos(tickDuration);
// Prevent overflow.
if (this.tickDuration >= Long.MAX_VALUE / wheel.length) {
throw new IllegalArgumentException(String.format(
"tickDuration: %d (expected: 0 < tickDuration in nanos < %d",
tickDuration, Long.MAX_VALUE / wheel.length));
}
workerThread = threadFactory.newThread(worker);
leak = leakDetector.open(this);
}
@SuppressWarnings("unchecked")
private static Set[] 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[] wheel = new Set[ticksPerWheel];
for (int i = 0; i < wheel.length; i ++) {
wheel[i] = Collections.newSetFromMap(
PlatformDependent.newConcurrentHashMap());
}
return wheel;
}
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 void start() {
switch (workerState.get()) {
case WORKER_STATE_INIT:
if (workerState.compareAndSet(WORKER_STATE_INIT, WORKER_STATE_STARTED)) {
workerThread.start();
}
break;
case WORKER_STATE_STARTED:
break;
case WORKER_STATE_SHUTDOWN:
throw new IllegalStateException("cannot be started once stopped");
default:
throw new Error("Invalid WorkerState");
}
}
@Override
public Set stop() {
if (Thread.currentThread() == workerThread) {
throw new IllegalStateException(
HashedWheelTimer.class.getSimpleName() +
".stop() cannot be called from " +
TimerTask.class.getSimpleName());
}
if (!workerState.compareAndSet(WORKER_STATE_STARTED, WORKER_STATE_SHUTDOWN)) {
// workerState can be 0 or 2 at this moment - let it always be 2.
workerState.set(WORKER_STATE_SHUTDOWN);
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();
}
leak.close();
Set unprocessedTimeouts = new HashSet();
for (Set bucket: wheel) {
unprocessedTimeouts.addAll(bucket);
bucket.clear();
}
return Collections.unmodifiableSet(unprocessedTimeouts);
}
@Override
public Timeout newTimeout(TimerTask task, long delay, TimeUnit unit) {
final long currentTime = System.nanoTime();
if (task == null) {
throw new NullPointerException("task");
}
if (unit == null) {
throw new NullPointerException("unit");
}
start();
long delayInNanos = unit.toNanos(delay);
HashedWheelTimeout timeout = new HashedWheelTimeout(task, currentTime + delayInNanos);
scheduleTimeout(timeout, delayInNanos);
return timeout;
}
void scheduleTimeout(HashedWheelTimeout timeout, long delay) {
// Prepare the required parameters to schedule the timeout object.
long relativeIndex = (delay + tickDuration - 1) / tickDuration;
// if the previous line had an overflow going on, then we’ll just schedule this timeout
// one tick early; that shouldn’t matter since we’re talking 270 years here
if (relativeIndex < 0) {
relativeIndex = delay / tickDuration;
}
if (relativeIndex == 0) {
relativeIndex = 1;
}
if ((relativeIndex & mask) == 0) {
relativeIndex--;
}
final long remainingRounds = relativeIndex / wheel.length;
// Add the timeout to the wheel.
lock.readLock().lock();
try {
if (workerState.get() == WORKER_STATE_SHUTDOWN) {
throw new IllegalStateException("Cannot enqueue after shutdown");
}
final 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() {
}
@Override
public void run() {
List expiredTimeouts =
new ArrayList();
startTime = System.nanoTime();
tick = 1;
while (workerState.get() == WORKER_STATE_STARTED) {
final long deadline = waitForNextTick();
if (deadline > 0) {
fetchExpiredTimeouts(expiredTimeouts, deadline);
notifyExpiredTimeouts(expiredTimeouts);
}
}
}
private void fetchExpiredTimeouts(
List 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;
fetchExpiredTimeouts(expiredTimeouts, wheel[newWheelCursor].iterator(), deadline);
} finally {
lock.writeLock().unlock();
}
}
private void fetchExpiredTimeouts(
List expiredTimeouts,
Iterator i, long deadline) {
List slipped = null;
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();
}
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 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();
}
/**
* calculate goal nanoTime from startTime and current tick number,
* then wait until that goal has been reached.
* @return Long.MIN_VALUE if received a shutdown request,
* current time otherwise (with Long.MIN_VALUE changed by +1)
*/
private long waitForNextTick() {
long deadline = startTime + tickDuration * tick;
for (;;) {
final long currentTime = System.nanoTime();
long sleepTimeMs = (deadline - currentTime + 999999) / 1000000;
if (sleepTimeMs <= 0) {
tick += 1;
if (currentTime == Long.MIN_VALUE) {
return -Long.MAX_VALUE;
} else {
return currentTime;
}
}
// Check if we run on windows, as if thats the case we will need
// to round the sleepTime as workaround for a bug that only affect
// the JVM if it runs on windows.
//
// See https://github.com/netty/netty/issues/356
if (PlatformDependent.isWindows()) {
sleepTimeMs = sleepTimeMs / 10 * 10;
}
try {
Thread.sleep(sleepTimeMs);
} catch (InterruptedException e) {
if (workerState.get() == WORKER_STATE_SHUTDOWN) {
return Long.MIN_VALUE;
}
}
}
}
}
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;
}
@Override
public Timer timer() {
return HashedWheelTimer.this;
}
@Override
public TimerTask task() {
return task;
}
@Override
public boolean cancel() {
if (!state.compareAndSet(ST_INIT, ST_CANCELLED)) {
return false;
}
wheel[stopIndex].remove(this);
return true;
}
@Override
public boolean isCancelled() {
return state.get() == ST_CANCELLED;
}
@Override
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() {
final long currentTime = System.nanoTime();
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();
}
}
}