Java多线程之新类库中的构件DelayQueue

 

DelayQueue

是一个无界的BlockingQueue，用于放置实现了Delayed接口的对象，其中的对象只能在其到期时才能从队列中取走。这种队列是有序的，即队头对象的延迟到期时间最长。注意：不能将null元素放置到这种队列中。

 

Delayed

 

一种混合风格的接口，用来标记那些应该在给定延迟时间之后执行的对象。

此接口的实现必须定义一个 compareTo 方法，该方法提供与此接口的 getDelay 方法一致的排序。

package concurrent;

import java.util.Random;  
import java.util.concurrent.DelayQueue;  
import java.util.concurrent.Delayed;  
import java.util.concurrent.ExecutorService;  
import java.util.concurrent.Executors;  
import java.util.concurrent.TimeUnit;  
  
/** 
 * 模拟考试，时间为120分钟，学生可以再30分钟后交卷， 
 * 当学生都交完了 或 时间到者考试结束 
 * @author 小e 
 * 
 * 2010-4-30 下午11:14:25 
 */  
class Student implements Runnable,Delayed{  
    private String name;  
    private long submitTime;//交卷时间  
    private long workTime;//考试时间  
    public Student() {  
        // TODO Auto-generated constructor stub  
    }  
    public Student(String name, long submitTime) {  
        super();  
        this.name = name;  
        workTime = submitTime;  
        //都转为转为ns  
        this.submitTime = TimeUnit.NANOSECONDS.convert(submitTime, TimeUnit.MILLISECONDS) + System.nanoTime();  
    }  
  
    @Override  
    public void run() {  
        System.out.println(name + " 交卷,用时" + workTime/100 + "分钟");  
    }  
  
    @Override  
    public long getDelay(TimeUnit unit) {  
        return unit.convert(submitTime - System.nanoTime(), unit.NANOSECONDS);  
    }  
  
    @Override  
    public int compareTo(Delayed o) {  
        Student that = (Student) o;  
        return submitTime > that.submitTime?1:(submitTime < that.submitTime ? -1 : 0);  
    }  
    public static class EndExam extends Student{  
        private ExecutorService exec;  
        public EndExam(int submitTime,ExecutorService exec) {  
            super(null,submitTime);  
            this.exec = exec;  
        }  
        @Override  
        public void run() {  
            exec.shutdownNow();  
        }  
    }  
      
}  
class Teacher implements Runnable{  
    private DelayQueue<Student> students;  
    private ExecutorService exec;  
      
    public Teacher(DelayQueue<Student> students,ExecutorService exec) {  
        super();  
        this.students = students;  
        this.exec = exec;  
    }  
  
  
    @Override  
    public void run() {  
        try {  
            System.out.println("考试开始……");  
            while (!Thread.interrupted()) {  
                students.take().run();  
            }  
            System.out.println("考试结束……");  
        } catch (InterruptedException e) {  
            e.printStackTrace();  
        }  
  
    }  
      
}  
public class Exam {  
    static final int STUDENT_SIZE = 45;  
    public static void main(String[] args) {  
        Random r = new Random();  
        DelayQueue<Student> students = new DelayQueue<Student>();  
        ExecutorService exec = Executors.newCachedThreadPool();  
        for(int i = 0; i < STUDENT_SIZE; i++){  
            students.put(new Student("学生" + ( i + 1), 3000 + r.nextInt(9000)));  
        }  
        students.put(new Student.EndExam(12000,exec));//1200为考试结束时间  
        exec.execute(new Teacher(students, exec));  
          
    }  
  
}