java.util.concurrent.DelayQueue可以忽略过期的元素

Question

下面的Java代码示例使用java DelayQueue来处理任务.但是,从另一个线程插入任务似乎会破坏(我的)预期行为.

抱歉代码示例如此之长,但总结如下:

1. 主线程向DelayQueue添加5个任务(AE),具有各种延迟(0ms,10ms,100ms 1000ms,10000ms)
2. 启动另一个步骤,在3000ms后向DelayQueue添加另一个任务
3. 主线程轮询DelayQueue并报告每个任务到期
4. 在8000ms之后,主线程报告DelayQueue中剩余的任务

我从代码示例中获得的输出是:

------initial tasks ---------------
task A due in 0ms
task B due in 9ms
task C due in 99ms
task D due in 999ms
task E due in 9999ms
task F due in 99999ms
------processing--------------------
time = 5    task A due in -1ms
time = 14   task B due in 0ms
time = 104  task C due in 0ms
time = 1004 task D due in 0ms
time = 3003 added task Z due in 0ms
------remaining after 15007ms -----------
task F due in 84996ms
task E due in -5003ms
task Z due in -12004ms

我的问题是:为什么在15000ms之后,DelayQueue中还有剩余的任务(即GetDelay()返回-ve值)？

我检查过的一些事情:

• 我已经实现了compareTo()来定义任务的自然顺序
• equals()与compareTo()一致
• hashCode()已被覆盖

我将最感兴趣的是学习如何解决这个问题.提前感谢您的协助.(以及帮助我​​约会的所有Stack Overflow答案:)

    package test;

    import java.util.concurrent.DelayQueue;
    import java.util.concurrent.Delayed;
    import java.util.concurrent.TimeUnit;

    public class Test10_DelayQueue {

       private static final TimeUnit delayUnit = TimeUnit.MILLISECONDS;
       private static final TimeUnit ripeUnit = TimeUnit.NANOSECONDS;

       static long startTime;

       static class Task implements Delayed {    
          public long ripe;
          public String name;    
          public Task(String name, int delay) {
             this.name = name;
             ripe = System.nanoTime() + ripeUnit.convert(delay, delayUnit);
          }

      @Override
      public boolean equals(Object obj) {
         if (obj instanceof Task) {
            return compareTo((Task) obj) == 0;
         }
         return false;
      }

      @Override
      public int hashCode() {
         int hash = 7;
         hash = 67 * hash + (int) (this.ripe ^ (this.ripe >>> 32));
         hash = 67 * hash + (this.name != null ? this.name.hashCode() : 0);
         return hash;
      }

      @Override
      public int compareTo(Delayed delayed) {
         if (delayed instanceof Task) {
            Task that = (Task) delayed;
            return (int) (this.ripe - that.ripe);
         }
         throw new UnsupportedOperationException();
      }

      @Override
      public long getDelay(TimeUnit unit) {
         return unit.convert(ripe - System.nanoTime(), ripeUnit);
      }

      @Override
      public String toString() {
         return "task " + name + " due in " + String.valueOf(getDelay(delayUnit) + "ms");
          }
       }

       static class TaskAdder implements Runnable {

      DelayQueue dq;
      int delay;

      public TaskAdder(DelayQueue dq, int delay) {
         this.dq = dq;
         this.delay = delay;
      }

      @Override
      public void run() {
         try {
            Thread.sleep(delay);

            Task z = new Task("Z", 0);
            dq.add(z);

            Long elapsed = System.currentTimeMillis() - startTime;

            System.out.println("time = " + elapsed + "\tadded " + z);

         } catch (InterruptedException e) {
         }
      }
    }

    public static void main(String[] args) {
      startTime = System.currentTimeMillis();
      DelayQueue<Task> taskQ = new DelayQueue<Task>();

      Thread thread = new Thread(new TaskAdder(taskQ, 3000));
      thread.start();

      taskQ.add(new Task("A", 0));
      taskQ.add(new Task("B", 10));
      taskQ.add(new Task("C", 100));
      taskQ.add(new Task("D", 1000));
      taskQ.add(new Task("E", 10000));
      taskQ.add(new Task("F", 100000));

      System.out.println("------initial tasks ---------------");
      Task[] tasks = taskQ.toArray(new Task[0]);
      for (int i = 0; i < tasks.length; i++) {
         System.out.println(tasks[i]);
      }

      System.out.println("------processing--------------------");
      try {
         Long elapsed = System.currentTimeMillis() - startTime;
         while (elapsed < 15000) {
            Task task = taskQ.poll(1, TimeUnit.SECONDS);
            elapsed = System.currentTimeMillis() - startTime;
            if (task != null) {
               System.out.println("time = " + elapsed + "\t" + task);
            }
         }

         System.out.println("------remaining after " + elapsed + "ms -----------");
         tasks = taskQ.toArray(new Task[0]);
         for (int i = 0; i < tasks.length; i++) {
            System.out.println(tasks[i]);
         }

      } catch (InterruptedException e) {
      }
    }
    }

Answer 1

因为你的comapareTo方法充满了缺陷。正确的实现如下。一旦你像下面这样改变，你的所有问题都会得到解决。compareTo如果或遵守compareTo合同，请始终尝试重用方法

return Long.valueOf(this.ripe).compareTo(that.ripe);

Answer 2

原因是数值溢出.

你的compareTo()方法是以long纳秒为单位施加差异int,但超过2.2秒的纳秒数不能保持在一个int并且你会得到一个溢出 - 给出或多或少的随机结果,所以队列中的顺序可能落后于一个如果将来超过2.2秒,则会延迟到期.

poll()不会超出队列中的下一个项目,compareTo当项目放入队列时,该方法的顺序由方法定义.

此外,equals()应该同意hashCode(),以及compareTo().有关详细信息,请参阅javadochashCode().