Lock和读写锁ReadWriteLock和缓存实例

1：lock和synchronized对比

[java] view plain copy

1. import java.util.concurrent.locks.Lock;  
2. import java.util.concurrent.locks.ReentrantLock;  
3.   
4.   
5. public class LockTest {  
6.   
7.     /** 
8.      * @param args 
9.      */  
10.     public static void main(String[] args) {  
11.         new LockTest().init();  
12.     }  
13.       
14.     private void init(){  
15.         final Outputer outputer = new Outputer();  
16.         new Thread(new Runnable(){  
17.             @Override  
18.             public void run() {  
19.                 while(true){  
20.                     try {  
21.                         Thread.sleep(10);  
22.                     } catch (InterruptedException e) {  
23.                         // TODO Auto-generated catch block  
24.                         e.printStackTrace();  
25.                     }  
26.                     outputer.output("zhangxiaoxiang");  
27.                 }  
28.                   
29.             }  
30.         }).start();  
31.           
32.         new Thread(new Runnable(){  
33.             @Override  
34.             public void run() {  
35.                 while(true){  
36.                     try {  
37.                         Thread.sleep(10);  
38.                     } catch (InterruptedException e) {  
39.                         // TODO Auto-generated catch block  
40.                         e.printStackTrace();  
41.                     }  
42.                     outputer.output("lihuoming");  
43.                 }  
44.                   
45.             }  
46.         }).start();  
47.           
48.     }  
49.   
50.     static class Outputer{  
51.         Lock lock = new ReentrantLock();  
52.         public void output(String name){  
53.             int len = name.length();  
54.             lock.lock();  
55.             try{  
56.                 for(int i=0;i<len;i++){  
57.                     System.out.print(name.charAt(i));  
58.                 }  
59.                 System.out.println();  
60.             }finally{  
61.                 lock.unlock();  
62.             }  
63.         }  
64.           
65.         public synchronized void output2(String name){  
66.             int len = name.length();  
67.             for(int i=0;i<len;i++){  
68.                     System.out.print(name.charAt(i));  
69.             }  
70.             System.out.println();  
71.         }  
72.           
73.         public static synchronized void output3(String name){  
74.             int len = name.length();  
75.             for(int i=0;i<len;i++){  
76.                     System.out.print(name.charAt(i));  
77.             }  
78.             System.out.println();  
79.         }     
80.     }  
81. }  

2.读写锁：ReadWriteLock

[java] view plain copy

1. import java.util.Random;  
2. import java.util.concurrent.locks.ReadWriteLock;  
3. import java.util.concurrent.locks.ReentrantReadWriteLock;  
4.   
5. public class ReadWriteLockTest {  
6.     public static void main(String[] args) {  
7.         final Queue3 q3 = new Queue3();  
8.         for(int i=0;i<3;i++)  
9.         {  
10.             new Thread(){  
11.                 public void run(){  
12.                     while(true){  
13.                         q3.get();                         
14.                     }  
15.                 }  
16.                   
17.             }.start();  
18.   
19.             new Thread(){  
20.                 public void run(){  
21.                     while(true){  
22.                         q3.put(new Random().nextInt(10000));  
23.                     }  
24.                 }             
25.                   
26.             }.start();  
27.         }  
28.           
29.     }  
30. }  
31.   
32. class Queue3{  
33.     private Object data = null;//共享数据，只能有一个线程能写该数据，但可以有多个线程同时读该数据。  
34.     ReadWriteLock rwl = new ReentrantReadWriteLock();  
35.     public void get(){  
36.         rwl.readLock().lock();  
37.         try {  
38.             System.out.println(Thread.currentThread().getName() + " be ready to read data!");  
39.             Thread.sleep((long)(Math.random()*1000));  
40.             System.out.println(Thread.currentThread().getName() + "have read data :" + data);             
41.         } catch (InterruptedException e) {  
42.             e.printStackTrace();  
43.         }finally{  
44.             rwl.readLock().unlock();  
45.         }  
46.     }  
47.       
48.     public void put(Object data){  
49.   
50.         rwl.writeLock().lock();  
51.         try {  
52.             System.out.println(Thread.currentThread().getName() + " be ready to write data!");                    
53.             Thread.sleep((long)(Math.random()*1000));  
54.             this.data = data;         
55.             System.out.println(Thread.currentThread().getName() + " have write data: " + data);                   
56.         } catch (InterruptedException e) {  
57.             e.printStackTrace();  
58.         }finally{  
59.             rwl.writeLock().unlock();  
60.         }  
61.           
62.       
63.     }  
64. }  

3.用写锁实现库存递减

import java.util.concurrent.locks.ReadWriteLock;import java.util.concurrent.locks.ReentrantReadWriteLock;public class ReadWriteLockTest {public static boolean flag = true;public static void main(String[] args) {final Queue3 q3 = new Queue3();for (int i = 0; i < 3; i++) {new Thread() {public void run() {while (ReadWriteLockTest.flag) {q3.put();}}}.start();}}}class Queue3 {private Integer data = 10;// 共享数据，只能有一个线程能写该数据，但可以有多个线程同时读该数据。final ReadWriteLock lock = new ReentrantReadWriteLock();public void put() {lock.writeLock().lock();// 写锁开启，这时只有一个写线程进入try {System.out.println(Thread.currentThread().getName() + " have write data: " + data);if (data == 0) {ReadWriteLockTest.flag = false;return;}data--;} finally {lock.writeLock().unlock();}}}

4.用读写锁实现一个简单缓存机制

[java] view plain copy

1. import java.util.HashMap;  
2. import java.util.Map;  
3. import java.util.concurrent.locks.ReadWriteLock;  
4. import java.util.concurrent.locks.ReentrantReadWriteLock;  
5.   
6. public class CacheDemo {  
7.   
8.     private Map<String, Object> cache = new HashMap<String, Object>();  
9.     public static void main(String[] args) {  
10.         // TODO Auto-generated method stub  
11.   
12.     }  
13.   
14.     private ReadWriteLock rwl = new ReentrantReadWriteLock();  
15.     public  Object getData(String key){  
16.         rwl.readLock().lock();  
17.         Object value = null;  
18.         try{  
19.             value = cache.get(key);  
20.             if(value == null){  
21.                 rwl.readLock().unlock();  
22.                 rwl.writeLock().lock();  
23.                 try{  
24.                     if(value==null){  
25.                         value = "aaaa";//实际失去queryDB();  
26.                     }  
27.                 }finally{  
28.                     rwl.writeLock().unlock();  
29.                 }  
30.                 rwl.readLock().lock();  
31.             }  
32.         }finally{  
33.             rwl.readLock().unlock();  
34.         }  
35.         return value;  
36.     }  
37. }