c语言sscanf函数的用法是什么
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2023-01-23
java简单手写版本实现时间轮算法
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
*/
@Slf4j
public 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
public TimeWheel(long tickMs, int wheelSize, long currentTime, 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
*/
@Slf4j
public 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
/**
* 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
@Slf4j
class 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 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
*/
@Data
class TimerTaskEntry implements Comparable
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
@Slf4j
class 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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