Java 优先级队列PriorityBlockingQueue 顺序问题记录

Love The Way You Lie 2022-10-23 12:53 131阅读 0赞

在使用优先级队列

PriorityBlockingQueue 时发现当出现相同优先级时，出队的顺序就和入队不相同

其根本原因是。。。

解决方法：

定义一个包装类，依赖第二种属性来排序相同优先级

package com.jwuwb.kids.stream;
    
    import java.util.concurrent.atomic.AtomicLong;
    
     /**
      * <E extends Comparable> 上限通配符指定接收Comparable 接口。
      * <? super E> 下限通配符，接收必须是E的父类。
      * <E extends Comparable<? super E>> 合起来表示接受实现了Comparable接口并且可以和其父类进行比较的类型E及其父类型。
      *
      * @param <E>
      */
    public class PackageEntry<E extends Comparable<? super E>> implements Comparable<PackageEntry<E>> {
        static final AtomicLong seq = new AtomicLong(0);
        final long seqNum;
    
        final E entry;
    
        public PackageEntry(E entry) {
            seqNum = seq.getAndIncrement();
            this.entry = entry;
       }
    
       public E getEntry() {
            return entry;
        }
    
        public int compareTo(PackageEntry<E> other) {
            int res = entry.compareTo(other.entry);
            if (res == 0 && other.entry != this.entry)
                res = (seqNum < other.seqNum ? -1 : 1);
            return res;
        }
    
        @Override
        public String toString() {
            return "PackageEntry{" +
                    "seqNum=" + seqNum +
                    ", entry=" + entry +
                    '}';
        }
    }

使用的话：

import com.google.common.collect.Maps;
    import com.jwuwb.kids.stream.quartz.CronUtil;
    import com.jwuwb.kids.stream.quartz.JobAndTriggerService;
    import com.jwuwb.kids.utils.DateTimeUtil;
    import com.jwuwb.kids.utils.UUIDUtil;
    import lombok.Getter;
    import lombok.Setter;
    import org.springframework.beans.factory.annotation.Autowired;
    import org.springframework.stereotype.Service;
    
    import java.text.ParseException;
    import java.time.LocalDateTime;
    import java.util.Map;
    import java.util.concurrent.PriorityBlockingQueue;
    
    /**
     * @program: kids
     * @description: 告警事件视频优先级队列
     * @author: zf
     * @create: 2021-03-03 17:39
     **/
    @Getter
    @Setter
    @Service
    public class WarnPriorityQueue implements Comparable<WarnPriorityQueue>{
        @Autowired
        private JobAndTriggerService jobAndTriggerService;
        private String msg;
        private Integer order;
        private String uid;
        private String tag;
    
        public WarnPriorityQueue() {
        }
    
        public WarnPriorityQueue(String msg, Integer order, String uid, String tag) {
            this.msg = msg;
            this.order = order;
            this.uid = uid;
            this.tag = tag;
        }
    
        public WarnPriorityQueue(String msg, Integer order, String tag) {
            this.msg = msg;
            this.order = order;
            this.uid = UUIDUtil.getUUIDStringWithNoHyphen();
            this.tag = tag;
        }
    
    
        @Override
        public int compareTo(WarnPriorityQueue o) {
                return this.order.compareTo(o.order);
        }
    
        /**
         * 优先级队列
         */
        public static final PriorityBlockingQueue<FifoEntry> priorityQueue =
                new PriorityBlockingQueue<>(11);
    
    
        public static void main(String[] args) throws InterruptedException {
            WarnPriorityQueue warnPriorityQueue = new WarnPriorityQueue();
            warnPriorityQueue.setMsg("1号");
            warnPriorityQueue.setOrder(2);
            warnPriorityQueue.setUid(UUIDUtil.getUUIDStringWithNoHyphen());
            WarnPriorityQueue warnPriorityQueue2 = new WarnPriorityQueue();
            warnPriorityQueue2.setMsg("2号");
            warnPriorityQueue2.setOrder(2);
            warnPriorityQueue2.setUid(UUIDUtil.getUUIDStringWithNoHyphen());
            WarnPriorityQueue warnPriorityQueue3 = new WarnPriorityQueue();
            warnPriorityQueue3.setMsg("3号");
            warnPriorityQueue3.setOrder(1);
            warnPriorityQueue3.setUid(UUIDUtil.getUUIDStringWithNoHyphen());
            WarnPriorityQueue warnPriorityQueue4 = new WarnPriorityQueue();
            warnPriorityQueue4.setMsg("4号");
            warnPriorityQueue4.setOrder(1);
            warnPriorityQueue4.setUid(UUIDUtil.getUUIDStringWithNoHyphen());
    
            priorityQueue.put(new FifoEntry<>(warnPriorityQueue));
            priorityQueue.put(new FifoEntry<>(warnPriorityQueue2));
            priorityQueue.put(new FifoEntry<>(warnPriorityQueue3));
            priorityQueue.put(new FifoEntry<>(warnPriorityQueue4));
            for (int i = 0; i < 4; i++) {
                WarnPriorityQueue entry = (WarnPriorityQueue) priorityQueue.take().entry;
                System.out.println(entry.getMsg());
    
            }
        }
    }