java简单手写版本实现时间轮算法

时间轮

关于时间轮的介绍,网上有很多,这里就不重复了

核心思想 一个环形数组存储时间轮的所有槽(看你的手表),每个槽对应当前时间轮的最小精度 超过当前时间轮最大表示范围的会被丢到上层时间轮,上层时间轮的最小精度即为下层时间轮能表达的最大时间(时分秒概念) 每个槽对应一个环形链表存储该时间应该被执行的任务 需要一个线程去驱动指针运转,获取到期任务

以下给出java 简单手写版本实现

代码实现

时间轮主数据结构

/** * @author apdoer * @version 1.0 * @date 2021/3/22 19:31 */@Slf4jpublic class TimeWheel { /** * 一个槽的时间间隔(时间轮最小刻度) */ private long tickMs; /** * 时间轮大小(槽的个数) */ private int wheelSize; /** * 一轮的时间跨度 */ private long interval; private long currentTime; /** * 槽 */ private TimerTaskList[] buckets; /** * 上层时间轮 */ private volatile TimeWheel overflowWheel; /** * 一个timer只有一个delayqueue */ private DelayQueue<TimerTaskList> delayQueue; public TimeWheel(long tickMs, int wheelSize, long currentTime, DelayQueue<TimerTaskList> delayQueue) { this.currentTime = currentTime; this.tickMs = tickMs; this.wheelSize = wheelSize; this.interval = tickMs * wheelSize; this.buckets = new TimerTaskList[wheelSize]; this.currentTime = currentTime - (currentTime % tickMs); this.delayQueue = delayQueue; for (int i = 0; i < wheelSize; i++) { buckets[i] = new TimerTaskList(); } } public boolean add(TimerTaskEntry entry) { long expiration = entry.getExpireMs(); if (expiration < tickMs + currentTime) { //到期了 return false; } else if (expiration < currentTime + interval) { //扔进当前时间轮的某个槽里,只有时间大于某个槽,才会放进去 long virtualId = (expiration / tickMs); int index = (int) (virtualId % wheelSize); TimerTaskList bucket = buckets[index]; bucket.addTask(entry); //设置bucket 过期时间 if (bucket.setExpiration(virtualId * tickMs)) {//设好过期时间的bucket需要入队delayQueue.offer(bucket);return true; } } else { //当前轮不能满足,需要扔到上一轮 TimeWheel timeWheel = getOverflowWheel(); return timeWheel.add(entry); } return false; } private TimeWheel getOverflowWheel() { if (overflowWheel == null) { synchronized (this) {if (overflowWheel == null) { overflowWheel = new TimeWheel(interval, wheelSize, currentTime, delayQueue);} } } return overflowWheel; } /** * 推进指针 * * @param timestamp */ public void advanceLock(long timestamp) { if (timestamp > currentTime + tickMs) { currentTime = timestamp - (timestamp % tickMs); if (overflowWheel != null) {this.getOverflowWheel().advanceLock(timestamp); } } }}

定时器接口

/** * 定时器 * @author apdoer * @version 1.0 * @date 2021/3/22 20:30 */public interface Timer { /** * 添加一个新任务 * * @param timerTask */ void add(TimerTask timerTask); /** * 推动指针 * * @param timeout */ void advanceClock(long timeout); /** * 等待执行的任务 * * @return */ int size(); /** * 关闭服务,剩下的无法被执行 */ void shutdown();}

定时器实现

/** * @author apdoer * @version 1.0 * @date 2021/3/22 20:33 */@Slf4jpublic class SystemTimer implements Timer { /** * 底层时间轮 */ private TimeWheel timeWheel; /** * 一个Timer只有一个延时队列 */ private DelayQueue<TimerTaskList> delayQueue = new DelayQueue<>(); /** * 过期任务执行线程 */ private ExecutorService workerThreadPool; /** * 轮询delayQueue获取过期任务线程 */ private ExecutorService bossThreadPool; public SystemTimer() { this.timeWheel = new TimeWheel(1, 20, System.currentTimeMillis(), delayQueue); this.workerThreadPool = Executors.newFixedThreadPool(100); this.bossThreadPool = Executors.newFixedThreadPool(1); //20ms推动一次时间轮运转 this.bossThreadPool.submit(() -> { for (; ; ) {this.advanceClock(20); } }); } public void addTimerTaskEntry(TimerTaskEntry entry) { if (!timeWheel.add(entry)) { //已经过期了 TimerTask timerTask = entry.getTimerTask(); log.info('=====任务:{} 已到期,准备执行============',timerTask.getDesc()); workerThreadPool.submit(timerTask); } } @Override public void add(TimerTask timerTask) { log.info('=======添加任务开始====task:{}', timerTask.getDesc()); TimerTaskEntry entry = new TimerTaskEntry(timerTask, timerTask.getDelayMs() + System.currentTimeMillis()); timerTask.setTimerTaskEntry(entry); addTimerTaskEntry(entry); } /** * 推动指针运转获取过期任务 * * @param timeout 时间间隔 * @return */ @Override public synchronized void advanceClock(long timeout) { try { TimerTaskList bucket = delayQueue.poll(timeout, TimeUnit.MILLISECONDS); if (bucket != null) {//推进时间timeWheel.advanceLock(bucket.getExpiration());//执行过期任务(包含降级)bucket.clear(this::addTimerTaskEntry); } } catch (InterruptedException e) { log.error('advanceClock error'); } } @Override public int size() { //todo return 0; } @Override public void shutdown() { this.bossThreadPool.shutdown(); this.workerThreadPool.shutdown(); this.timeWheel = null; }}

存储任务的环形链表

/** * @author apdoer * @version 1.0 * @date 2021/3/22 19:26 */@Data@Slf4jclass TimerTaskList implements Delayed { /** * TimerTaskList 环形链表使用一个虚拟根节点root */ private TimerTaskEntry root = new TimerTaskEntry(null, -1); { root.next = root; root.prev = root; } /** * bucket的过期时间 */ private AtomicLong expiration = new AtomicLong(-1L); public long getExpiration() { return expiration.get(); } /** * 设置bucket的过期时间,设置成功返回true * * @param expirationMs * @return */ boolean setExpiration(long expirationMs) { return expiration.getAndSet(expirationMs) != expirationMs; } public boolean addTask(TimerTaskEntry entry) { boolean done = false; while (!done) { //如果TimerTaskEntry已经在别的list中就先移除,同步代码块外面移除,避免死锁,一直到成功为止 entry.remove(); synchronized (this) {if (entry.timedTaskList == null) { //加到链表的末尾 entry.timedTaskList = this; TimerTaskEntry tail = root.prev; entry.prev = tail; entry.next = root; tail.next = entry; root.prev = entry; done = true;} } } return true; } /** * 从 TimedTaskList 移除指定的 timerTaskEntry * * @param entry */ public void remove(TimerTaskEntry entry) { synchronized (this) { if (entry.getTimedTaskList().equals(this)) {entry.next.prev = entry.prev;entry.prev.next = entry.next;entry.next = null;entry.prev = null;entry.timedTaskList = null; } } } /** * 移除所有 */ public synchronized void clear(Consumer<TimerTaskEntry> entry) { TimerTaskEntry head = root.next; while (!head.equals(root)) { remove(head); entry.accept(head); head = root.next; } expiration.set(-1L); } @Override public long getDelay(TimeUnit unit) { return Math.max(0, unit.convert(expiration.get() - System.currentTimeMillis(), TimeUnit.MILLISECONDS)); } @Override public int compareTo(Delayed o) { if (o instanceof TimerTaskList) { return Long.compare(expiration.get(), ((TimerTaskList) o).expiration.get()); } return 0; }}

存储任务的容器entry

/** * @author apdoer * @version 1.0 * @date 2021/3/22 19:26 */@Dataclass TimerTaskEntry implements Comparable<TimerTaskEntry> { private TimerTask timerTask; private long expireMs; volatile TimerTaskList timedTaskList; TimerTaskEntry next; TimerTaskEntry prev; public TimerTaskEntry(TimerTask timedTask, long expireMs) { this.timerTask = timedTask; this.expireMs = expireMs; this.next = null; this.prev = null; } void remove() { TimerTaskList currentList = timedTaskList; while (currentList != null) { currentList.remove(this); currentList = timedTaskList; } } @Override public int compareTo(TimerTaskEntry o) { return ((int) (this.expireMs - o.expireMs)); }}

任务包装类(这里也可以将工作任务以线程变量的方式去传入)

@Data@Slf4jclass TimerTask implements Runnable { /** * 延时时间 */ private long delayMs; /** * 任务所在的entry */ private TimerTaskEntry timerTaskEntry; private String desc; public TimerTask(String desc, long delayMs) { this.desc = desc; this.delayMs = delayMs; this.timerTaskEntry = null; } public synchronized void setTimerTaskEntry(TimerTaskEntry entry) { // 如果这个timetask已经被一个已存在的TimerTaskEntry持有,先移除一个 if (timerTaskEntry != null && timerTaskEntry != entry) { timerTaskEntry.remove(); } timerTaskEntry = entry; } public TimerTaskEntry getTimerTaskEntry() { return timerTaskEntry; } @Override public void run() { log.info('============={}任务执行', desc); }}

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