Netty中时间轮HashWheelTimer源码.方便大家参考
/*
* 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.Collections;
import java.util.HashSet;
import java.util.Queue;
import java.util.Set;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.Executors;
import java.util.concurrent.RejectedExecutionException;
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.atomic.AtomicIntegerFieldUpdater;
import java.util.concurrent.atomic.AtomicLong;
import static io.netty.util.internal.StringUtil.simpleClassName;
/**
* 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 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 INSTANCE_COUNTER = new AtomicInteger();
private static final AtomicBoolean WARNED_TOO_MANY_INSTANCES = new AtomicBoolean();
private static final int INSTANCE_COUNT_LIMIT = 64;
private static final long MILLISECOND_NANOS = TimeUnit.MILLISECONDS.toNanos(1);
private static final ResourceLeakDetector<HashedWheelTimer> leakDetector = ResourceLeakDetectorFactory.instance()
.newResourceLeakDetector(HashedWheelTimer.class, 1);
private static final AtomicIntegerFieldUpdater<HashedWheelTimer> WORKER_STATE_UPDATER =
AtomicIntegerFieldUpdater.newUpdater(HashedWheelTimer.class, "workerState");
private final ResourceLeakTracker<HashedWheelTimer> leak;
private final Worker worker = new Worker();
private 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;
@SuppressWarnings({ "unused", "FieldMayBeFinal" })
private volatile int workerState; // 0 - init, 1 - started, 2 - shut down
private final long tickDuration;
private final HashedWheelBucket[] wheel;
private final int mask;
private final CountDownLatch startTimeInitialized = new CountDownLatch(1);
private final Queue<HashedWheelTimeout> timeouts = PlatformDependent.newMpscQueue();
private final Queue<HashedWheelTimeout> cancelledTimeouts = PlatformDependent.newMpscQueue();
private final AtomicLong pendingTimeouts = new AtomicLong(0);
private final long maxPendingTimeouts;
private volatile long startTime;
/**
* 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) {
this(threadFactory, tickDuration, unit, ticksPerWheel, true);
}
/**
* 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
* @param leakDetection {@code true} if leak detection should be enabled always,
* if false it will only be enabled if the worker thread is not
* a daemon thread.
* @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, boolean leakDetection) {
this(threadFactory, tickDuration, unit, ticksPerWheel, leakDetection, -1);
}
/**
* 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
* @param leakDetection {@code true} if leak detection should be enabled always,
* if false it will only be enabled if the worker thread is not
* a daemon thread.
* @param maxPendingTimeouts The maximum number of pending timeouts after which call to
* {@code newTimeout} will result in
* {@link java.util.concurrent.RejectedExecutionException}
* being thrown. No maximum pending timeouts limit is assumed if
* this value is 0 or negative.
* @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, boolean leakDetection,
long maxPendingTimeouts) {
//线程工厂，用于创建我们的worker线程
if (threadFactory == null) {
throw new NullPointerException("threadFactory");
}
//一个tick的时间单位
if (unit == null) {
throw new NullPointerException("unit");
}
//一个tick的时间间隔
if (tickDuration <= 0) {
throw new IllegalArgumentException("tickDuration must be greater than 0: " + tickDuration);
}
// 时间轮上一轮有多少个tick/bucket
if (ticksPerWheel <= 0) {
throw new IllegalArgumentException("ticksPerWheel must be greater than 0: " + ticksPerWheel);
}
// 将时间轮的大小规范到2的n次方，这样可以用位运算来处理mod操作，提高效率
// Normalize ticksPerWheel to power of two and initialize the wheel.
wheel = createWheel(ticksPerWheel);
// 计算位运算需要的源码
mask = wheel.length - 1;
// Convert tickDuration to nanos. 转时间间隔到纳秒
long duration = unit.toNanos(tickDuration);
// Prevent overflow. 防止溢出
if (duration >= Long.MAX_VALUE / wheel.length) {
throw new IllegalArgumentException(String.format(
"tickDuration: %d (expected: 0 < tickDuration in nanos < %d",
tickDuration, Long.MAX_VALUE / wheel.length));
}
// 时间间隔至少1ms
if (duration < MILLISECOND_NANOS) {
if (logger.isWarnEnabled()) {
logger.warn("Configured tickDuration %d smaller then %d, using 1ms.",
tickDuration, MILLISECOND_NANOS);
}
this.tickDuration = MILLISECOND_NANOS;
} else {
this.tickDuration = duration;
}
// 创建woker线程
workerThread = threadFactory.newThread(worker);
// 处理泄露监控（还未涉及）
leak = leakDetection || !workerThread.isDaemon() ? leakDetector.track(this) : null;
// 设置最大等待任务数
this.maxPendingTimeouts = maxPendingTimeouts;
// 限制timer实例数,避免太多的timer线程反而影响性能
if (INSTANCE_COUNTER.incrementAndGet() > INSTANCE_COUNT_LIMIT &&
WARNED_TOO_MANY_INSTANCES.compareAndSet(false, true)) {
reportTooManyInstances();
}
}
@Override
protected void finalize() throws Throwable {
try {
super.finalize();
} finally {
// This object is going to be GCed and it is assumed the ship has sailed to do a proper shutdown. If
// we have not yet shutdown then we want to make sure we decrement the active instance count.
if (WORKER_STATE_UPDATER.getAndSet(this, WORKER_STATE_SHUTDOWN) != WORKER_STATE_SHUTDOWN) {
INSTANCE_COUNTER.decrementAndGet();
}
}
}
private static HashedWheelBucket[] createWheel(int ticksPerWheel) {
// 时间轮数太小或太大抛出异常
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);
}
// 规范到2的n次方
ticksPerWheel = normalizeTicksPerWheel(ticksPerWheel);
HashedWheelBucket[] wheel = new HashedWheelBucket[ticksPerWheel];
for (int i = 0; i < wheel.length; i ++) {
wheel[i] = new HashedWheelBucket();
}
return wheel;
}
private static int normalizeTicksPerWheel(int ticksPerWheel) {
int normalizedTicksPerWheel = 1;
// 不断的左移,直到找到大于等于时间轮大小的2的n次方出现
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() {
// 针对worker状态进行switch
switch (WORKER_STATE_UPDATER.get(this)) {
// 如果是初始化状态
case WORKER_STATE_INIT:
// 如果cas更新到开始状态
if (WORKER_STATE_UPDATER.compareAndSet(this, WORKER_STATE_INIT, WORKER_STATE_STARTED)) {
// 启动worker线程
workerThread.start();
}
break;
// 如果已经处于启动状态,什么也不做
case WORKER_STATE_STARTED:
break;
// 如果已经shutdown, 那就进入了非法状态
case WORKER_STATE_SHUTDOWN:
throw new IllegalStateException("cannot be started once stopped");
default:
throw new Error("Invalid WorkerState");
}
// Wait until the startTime is initialized by the worker.
// 这里需要同步等待worker线程启动并完成startTime初始化的工作
while (startTime == 0) {
try {
startTimeInitialized.await();
} catch (InterruptedException ignore) {
// Ignore - it will be ready very soon.
}
}
}
/*
* 实现Timer中的接口
*/
@Override
public Set<Timeout> stop() {
// 判断当前线程是否是worker线程,stop方法不能由TimerTask触发
// 否则后面的同步等待join操作就无法完成
if (Thread.currentThread() == workerThread) {
throw new IllegalStateException(
HashedWheelTimer.class.getSimpleName() +
".stop() cannot be called from " +
TimerTask.class.getSimpleName());
}
// cas更新状态
if (!WORKER_STATE_UPDATER.compareAndSet(this, WORKER_STATE_STARTED, WORKER_STATE_SHUTDOWN)) {
// workerState can be 0 or 2 at this moment - let it always be 2.
if (WORKER_STATE_UPDATER.getAndSet(this, WORKER_STATE_SHUTDOWN) != WORKER_STATE_SHUTDOWN) {
INSTANCE_COUNTER.decrementAndGet();
if (leak != null) {
boolean closed = leak.close(this);
assert closed;
}
}
return Collections.emptySet();
}
// 走到这里, 那么之前的cas更新一切顺利
try {
boolean interrupted = false;
//while循环持续中断worker线程直到它醒悟他该结束了(有可能被一些耗时的操作耽误了)
// 通过isAlive判断worker线程是否已经结束
while (workerThread.isAlive()) {
workerThread.interrupt();
try {
workerThread.join(100);
} catch (InterruptedException ignored) {
interrupted = true;
}
}
// 如果当前线程被interrupt,就设置标志位
if (interrupted) {
Thread.currentThread().interrupt();
}
} finally {
// 减少实例数
INSTANCE_COUNTER.decrementAndGet();
if (leak != null) {
boolean closed = leak.close(this);
assert closed;
}
}
// 返回还没执行的定时任务
return worker.unprocessedTimeouts();
}
@Override
public Timeout newTimeout(TimerTask task, long delay, TimeUnit unit) {
if (task == null) {
throw new NullPointerException("task");
}
if (unit == null) {
throw new NullPointerException("unit");
}
// 增加等待执行的定时任务数
long pendingTimeoutsCount = pendingTimeouts.incrementAndGet();
// 如果超过最大数量就玩完
if (maxPendingTimeouts > 0 && pendingTimeoutsCount > maxPendingTimeouts) {
pendingTimeouts.decrementAndGet();
throw new RejectedExecutionException("Number of pending timeouts ("
+ pendingTimeoutsCount + ") is greater than or equal to maximum allowed pending "
+ "timeouts (" + maxPendingTimeouts + ")");
}
// 开启定时器
// 它的状态判断能够很好的处理多次启动
// 并且还能帮我们做一下状态判断
start();
// 计算这个任务的deadline，startTime是worker线程开始的时间戳
// Add the timeout to the timeout queue which will be processed on the next tick.
// During processing all the queued HashedWheelTimeouts will be added to the correct HashedWheelBucket.
//将超时添加到超时队列，超时队列将在下一次tick时处理。
//在处理过程中，所有排队的hashedwheeltimeout将被添加到正确的HashedWheelBucket中
long deadline = System.nanoTime() + unit.toNanos(delay) - startTime;
// Guard against overflow. 防止溢出
if (delay > 0 && deadline < 0) {
deadline = Long.MAX_VALUE;
}
// 直接创建一个HashedWheelTimeout句柄
HashedWheelTimeout timeout = new HashedWheelTimeout(this, task, deadline);
// 添加到等待执行的任务队列中
timeouts.add(timeout);
// 返回这个句柄
return timeout;
}
/**
* Returns the number of pending timeouts of this {@link Timer}.
*/
public long pendingTimeouts() {
return pendingTimeouts.get();
}
private static void reportTooManyInstances() {
if (logger.isErrorEnabled()) {
String resourceType = simpleClassName(HashedWheelTimer.class);
logger.error("You are creating too many " + resourceType + " instances. " +
resourceType + " is a shared resource that must be reused across the JVM," +
"so that only a few instances are created.");
}
}
private final class Worker implements Runnable {
private final Set<Timeout> unprocessedTimeouts = new HashSet<Timeout>();
private long tick;
@Override
public void run() {
// Initialize the startTime.
startTime = System.nanoTime();
if (startTime == 0) {
//我们在这里使用0作为未初始化值的指示器，所以确保初始化时它不是0
// We use 0 as an indicator for the uninitialized value here, so make sure it's not 0 when initialized.
startTime = 1;
}
// Notify the other threads waiting for the initialization at start().
// 通知还等待在start方法上的线程，我worker初始化好了
startTimeInitialized.countDown();
do {
// 等待下一个tick
final long deadline = waitForNextTick();
if (deadline > 0) {
// 获取下一个bucket的index，即当前tick mod bucket数量
int idx = (int) (tick & mask);
// 处理掉已取消的任务
processCancelledTasks();
// 获取当前要处理的bucket
HashedWheelBucket bucket =
wheel[idx];
// 将待处理的任务移动到它该去的bucket去
transferTimeoutsToBuckets();
// 处理掉当前bucket的所有到期定时任务
bucket.expireTimeouts(deadline);
tick++;
} // 除非当前的状态不是started，否则循环进行下一个tic
} while (WORKER_STATE_UPDATER.get(HashedWheelTimer.this) == WORKER_STATE_STARTED);
// Fill the unprocessedTimeouts so we can return them from stop() method.
// 到了这里，说明worker的状态已经不是started了，到了shutdown
// 那就得善后了，遍历所有的bucket，将还没来得及处理的任务全部清理到unprocessedTimeouts中
for (HashedWheelBucket bucket: wheel) {
bucket.clearTimeouts(unprocessedTimeouts);
}
// 遍历所有待处理并且还没取消的任务，添加到unprocessedTimeouts中
for (;;) {
HashedWheelTimeout timeout = timeouts.poll();
if (timeout == null) {
break;
}
if (!timeout.isCancelled()) {
unprocessedTimeouts.add(timeout);
}
}
// 处理所有的已取消的task，防止内存泄漏
// 其实我任务应该在结束的时候先处理已经取消的任务，这样似乎好理解一些
// 不过我理解如果我这样做有可能出现的问题是bucket里面会有任务残留
processCancelledTasks();
}
private void transferTimeoutsToBuckets() {
// transfer only max. 100000 timeouts per tick to prevent a thread to stale the workerThread when it just
// adds new timeouts in a loop.
// 最多一次转移100000个待分发定时任务到它们对应的bucket内
// 不然如果有一个线程一直添加定时任务就能让工作线程活生生饿死
for (int i = 0; i < 100000; i++) {
HashedWheelTimeout timeout = timeouts.poll();
if (timeout == null) {
// all processed
break;
}
// 如果已经取消就不管了
if (timeout.state() == HashedWheelTimeout.ST_CANCELLED) {
// Was cancelled in the meantime.
continue;
}
// 计算从worker线程开始运行算起要经过多少个tick才能到这个任务
long calculated = timeout.deadline / tickDuration;
// 计算这个任务要经过多少圈
timeout.remainingRounds = (calculated - tick) / wheel.length;
// 如果这个任务我们取晚了，那就让他在这个tick执行
final long ticks = Math.max(calculated, tick); // Ensure we don't schedule for past.
// 计算他应该到的bucket的index
int stopIndex = (int) (ticks & mask);
// 指派过去即可
HashedWheelBucket bucket = wheel[stopIndex];
bucket.addTimeout(timeout);
}
}
private void processCancelledTasks() {
// 毕竟取消的任务占极少数，所以这里就没有个数限制了
for (;;) {
// 取出一个取消的任务
HashedWheelTimeout timeout = cancelledTimeouts.poll();
if (timeout == null) {
// all processed
break;
}
try {
// 这里实际上是将它从它所属的bucket的双向链表中删除，这里后面会看到
timeout.remove();
} catch (Throwable t) {
if (logger.isWarnEnabled()) {
logger.warn("An exception was thrown while process a cancellation task", t);
}
}
}
}
/**
* 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() {
// 计算下一个tick的deadline
long deadline = tickDuration * (tick + 1);
// 循环直到当前时间来到了下一个tick
for (;;) {
// 计算当前时间
final long currentTime = System.nanoTime() - startTime;
// 计算需要sleep的毫秒数
long sleepTimeMs = (deadline - currentTime + 999999) / 1000000;
if (sleepTimeMs <= 0) {
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
// 处理一些windows才有的jvm bug
if (PlatformDependent.isWindows()) {
sleepTimeMs = sleepTimeMs / 10 * 10;
}
// 尝试sleep到下个tick的deadline
try {
Thread.sleep(sleepTimeMs);
} catch (InterruptedException ignored) {
// 如果发现已经被shutdown了，则返回MIN_VALUE，可以让run快速处理
if (WORKER_STATE_UPDATER.get(HashedWheelTimer.this) == WORKER_STATE_SHUTDOWN) {
return Long.MIN_VALUE;
}
}
}
}
public Set<Timeout> unprocessedTimeouts() {
return Collections.unmodifiableSet(unprocessedTimeouts);
}
}
private static 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 static final AtomicIntegerFieldUpdater<HashedWheelTimeout> STATE_UPDATER =
AtomicIntegerFieldUpdater.newUpdater(HashedWheelTimeout.class, "state");
private final HashedWheelTimer timer;
private final TimerTask task;
private final long deadline;
@SuppressWarnings({"unused", "FieldMayBeFinal", "RedundantFieldInitialization" })
private volatile int state = ST_INIT;
// remainingRounds will be calculated and set by Worker.transferTimeoutsToBuckets() before the
// HashedWheelTimeout will be added to the correct HashedWheelBucket.
long remainingRounds;
// This will be used to chain timeouts in HashedWheelTimerBucket via a double-linked-list.
// As only the workerThread will act on it there is no need for synchronization / volatile.
HashedWheelTimeout next;
HashedWheelTimeout prev;
// The bucket to which the timeout was added
HashedWheelBucket bucket;
HashedWheelTimeout(HashedWheelTimer timer, TimerTask task, long deadline) {
this.timer = timer;
this.task = task;
this.deadline = deadline;
}
@Override
public Timer timer() {
return timer;
}
@Override
public TimerTask task() {
return task;
}
@Override
public boolean cancel() {
// only update the state it will be removed from HashedWheelBucket on next tick.
if (!compareAndSetState(ST_INIT, ST_CANCELLED)) {
return false;
}
// If a task should be canceled we put this to another queue which will be processed on each tick.
// So this means that we will have a GC latency of max. 1 tick duration which is good enough. This way
// we can make again use of our MpscLinkedQueue and so minimize the locking / overhead as much as possible.
timer.cancelledTimeouts.add(this);
return true;
}
void remove() {
HashedWheelBucket bucket = this.bucket;
if (bucket != null) {
bucket.remove(this);
} else {
timer.pendingTimeouts.decrementAndGet();
}
}
public boolean compareAndSetState(int expected, int state) {
return STATE_UPDATER.compareAndSet(this, expected, state);
}
public int state() {
return state;
}
@Override
public boolean isCancelled() {
return state() == ST_CANCELLED;
}
@Override
public boolean isExpired() {
return state() == ST_EXPIRED;
}
public void expire() {
if (!compareAndSetState(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 + timer.startTime;
StringBuilder buf = new StringBuilder(192)
.append(simpleClassName(this))
.append('(')
.append("deadline: ");
if (remaining > 0) {
buf.append(remaining)
.append(" ns later");
} else if (remaining < 0) {
buf.append(-remaining)
.append(" ns ago");
} else {
buf.append("now");
}
if (isCancelled()) {
buf.append(", cancelled");
}
return buf.append(", task: ")
.append(task())
.append(')')
.toString();
}
}
/**
* Bucket that stores HashedWheelTimeouts. These are stored in a linked-list like datastructure to allow easy
* removal of HashedWheelTimeouts in the middle. Also the HashedWheelTimeout act as nodes themself and so no
* extra object creation is needed.
*/
private static final class HashedWheelBucket {
// Used for the linked-list datastructure
private HashedWheelTimeout head;
private HashedWheelTimeout tail;
/**
* Add {@link HashedWheelTimeout} to this bucket.
*/
public void addTimeout(HashedWheelTimeout timeout) {
assert timeout.bucket == null;
timeout.bucket = this;
if (head == null) {
head = tail = timeout;
} else {
tail.next = timeout;
timeout.prev = tail;
tail = timeout;
}
}
/**
* Expire all {@link HashedWheelTimeout}s for the given {@code deadline}.
*/
public void expireTimeouts(long deadline) {
// 获取双向链表的头
HashedWheelTimeout timeout = head;
// process all timeouts
// 从头到尾处理所有的任务
while (timeout != null) {
HashedWheelTimeout next = timeout.next;
// 如果剩余轮数小于0 说明需要马上执行
if (timeout.remainingRounds <= 0) {
// 将它从当前链表中移除
next = remove(timeout);
if (timeout.deadline <= deadline) {
// 执行timeout的逻辑
timeout.expire();
} else {
// The timeout was placed into a wrong slot. This should never happen.
throw new IllegalStateException(String.format(
"timeout.deadline (%d) > deadline (%d)", timeout.deadline, deadline));
}
} else if (timeout.isCancelled()) {
// 如果已经被取消，同样remove掉
next = remove(timeout);
} else {
// 否则将他们的轮数减一
timeout.remainingRounds --;
}
// 继续链表的遍历
timeout = next;
}
}
public HashedWheelTimeout remove(HashedWheelTimeout timeout) {
HashedWheelTimeout next = timeout.next;
// remove timeout that was either processed or cancelled by updating the linked-list
if (timeout.prev != null) {
timeout.prev.next = next;
}
if (timeout.next != null) {
timeout.next.prev = timeout.prev;
}
if (timeout == head) {
// if timeout is also the tail we need to adjust the entry too
if (timeout == tail) {
tail = null;
head = null;
} else {
head = next;
}
} else if (timeout == tail) {
// if the timeout is the tail modify the tail to be the prev node.
tail = timeout.prev;
}
// null out prev, next and bucket to allow for GC.
timeout.prev = null;
timeout.next = null;
timeout.bucket = null;
timeout.timer.pendingTimeouts.decrementAndGet();
return next;
}
/**
* Clear this bucket and return all not expired / cancelled {@link Timeout}s.
*/
public void clearTimeouts(Set<Timeout> set) {
for (;;) {
HashedWheelTimeout timeout = pollTimeout();
if (timeout == null) {
return;
}
if (timeout.isExpired() || timeout.isCancelled()) {
continue;
}
set.add(timeout);
}
}
private HashedWheelTimeout pollTimeout() {
HashedWheelTimeout head = this.head;
if (head == null) {
return null;
}
HashedWheelTimeout next = head.next;
if (next == null) {
tail = this.head = null;
} else {
this.head = next;
next.prev = null;
}
// null out prev and next to allow for GC.
head.next = null;
head.prev = null;
head.bucket = null;
return head;
}
}
}
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