2017-06-01 16:43阅读: 274评论: 0推荐: 1

多线程练习之有界的缓存

 1 package cn.sp.test;
 2 
 3 import java.util.concurrent.Semaphore;
 4 
 5 /**
 6  * 有界的缓存
 7  * @author pc
 8  *
 9  * @param <E>
10  */
11 public class BoundedBuffer<E> {
12     private final Semaphore availableItems;//可用项   信号量 
13     private final Semaphore availableSpaces;//可用空间  信号量 
14     private final E[] items;
15     private  int putPosition = 0,takePosition = 0;
16     
17     @SuppressWarnings("unchecked")
18     public BoundedBuffer(int capacity){
19         availableItems = new Semaphore(0);
20         availableSpaces = new Semaphore(capacity);
21         items = (E[]) new Object[capacity];
22     }
23     
24     public boolean isEmpty(){//可用许可为0
25         return availableItems.availablePermits() == 0;
26     }
27     
28     public  boolean isFull(){//满时可用空间为0
29         return availableSpaces.availablePermits() == 0 ;
30     }
31     
32     public void put(E x) throws InterruptedException{
33         availableSpaces.acquire();
34         doInsert(x);
35         availableItems.release();
36     }
37     
38     public E take() throws InterruptedException{
39         availableItems.acquire();//从 availableItems 获取 一个许可
40         E e = doExtract();
41         availableSpaces.release();//返回  一个许可 到 availableSpaces
42         return e;
43     }
44 
45     private synchronized E doExtract() {
46         int i = takePosition;
47         E x = items[i];
48         //取出后 调用垃圾收集器
49         items[i] = null;
50         takePosition = (++i == items.length)? 0 : i;
51         return x;
52     }
53 
54     private  synchronized void doInsert(E x) {//同步方法
55         int i = putPosition;
56         items[i] = x;
57         //如果满了重置为0
58         putPosition = (++i == items.length) ? 0 :i;
59         
60     }
61 }

测试类：

 1 package cn.sp.test;
 2 
 3 import org.junit.Assert;
 4 
 5 public class Test {
 6     
 7     public void test01(){
 8         BoundedBuffer<Integer> boundedBuffer = new BoundedBuffer<Integer>(10);
 9         Assert.assertTrue(boundedBuffer.isEmpty());
10         Assert.assertFalse(boundedBuffer.isFull());
11     }
12     @org.junit.Test
13     public void test02() throws InterruptedException{
14         BoundedBuffer<Integer> boundedBuffer = new BoundedBuffer<Integer>(10);
15         
16         for(int i=0;i<10;i++){
17             boundedBuffer.put(i);
18         }
19         Assert.assertTrue(boundedBuffer.isFull());
20         Assert.assertFalse(boundedBuffer.isEmpty());
21         System.out.println(boundedBuffer.isFull());
22     }
23 }