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Android中Sqlite数据库多线程并发问题

最近在做一个Android项目, 为了改善用户体验,把原先必须让用户“等待”的过程改成在新线程中异步执行。但是这样做遇到了多个线程同时需要写Sqlite数据库,导致操作数据库失败。

本人对JAVA并不熟悉,只接触了2个多月(纯粹为了Android项目, 才开始接触JAVA), 在网上搜了一下, 发现JAVA在线程同步方面提供的功能相对于C#真少,只找到synchronized关键字, 而且还不提供timeout机制, 不过经过测试, 至少解决了目前的需求。

问题需求:

1. Android中, 对Sqlite数据库操作, 需要自己实现一个继承自SQLiteOpenHelper的类

2. 实现类中, 对数据库read操作不需要同步(提高效率)

3. 实现类中, 所有对数据库写操作, 必须要同步

解决方法:

定义一个private final static byte[] _writeLock = new byte[0]; 作为写锁

static  保证多个实例之间, 使用的是同一个对象(同一把锁)

final 保证锁对象不会被修改

测试代码:

01 package com.yushiro;
02   
03   
04 public class multiThreadTest {
05   
06     private final static byte[] _writeLock = new byte[0];
07     private static int _syncInt = 0;
08     public void Method1(){
09         synchronized (_writeLock) {
10             StringBuffer sb = new StringBuffer();
11             sb.append(Thread.currentThread().getName());
12             sb.append(" Method1 ");
13             sb.append(_syncInt);
14             _syncInt++;
15             sb.append(" --> ");
16             sb.append(_syncInt);
17             System.out.println(sb.toString());
18         }
19     }
20       
21     public void Method2(){
22         synchronized (_writeLock) {
23             StringBuffer sb = new StringBuffer();
24             sb.append(Thread.currentThread().getName());
25             sb.append(" Method2 ");
26             sb.append(_syncInt);
27             _syncInt++;
28             sb.append(" --> ");
29             sb.append(_syncInt);
30             System.out.println(sb.toString());      }
31     }
32       
33     public void Method3(){
34         synchronized (_writeLock) {
35             this.Method1();
36             this.Method2();
37             }
38     }
39 }
01 package com.yushiro;
02   
03   
04 public class MainTest {
05   
06       
07     public static void main(String[] args) {
08           
09         Thread t2= new Thread1();
10         Thread t1= new Thread2();
11         Thread t3 = new Thread3();
12         t1.start();
13         t2.start();
14         t3.start();
15     }
16   
17     private static class Thread2 extends Thread {
18         public void run() {
19             multiThreadTest tmp = new multiThreadTest();
20             while(true) {
21                   
22                   
23                 try {
24                     Thread.sleep(30000);
25                     tmp.Method1();
26                 } catch (InterruptedException e) {
27                     // TODO Auto-generated catch block
28                     e.printStackTrace();
29                 }
30                   
31                 //System.out.println(y);
32             }
33         }
34     }
35       
36     private static class Thread1 extends Thread {
37         public void run() {
38             multiThreadTest tmp = new multiThreadTest();
39             while(true) {
40                   
41                   
42                 try {
43                     Thread.sleep(100);
44                     tmp.Method2();
45                     Thread.sleep(100);
46                     tmp.Method1();
47                 } catch (InterruptedException e) {
48                     // TODO Auto-generated catch block
49                     e.printStackTrace();
50                 }
51                   
52                 //System.out.println(y);
53             }
54         }
55     }
56     private static class Thread3 extends Thread {
57         public void run() {
58             multiThreadTest tmp = new multiThreadTest();
59             while(true) {
60                   
61                   
62                 try {
63                     Thread.sleep(100);
64                     tmp.Method3();
65                 } catch (InterruptedException e) {
66                     // TODO Auto-generated catch block
67                     e.printStackTrace();
68                 }
69                   
70                 //System.out.println(y);
71             }
72         }
73     }
74   
75 }

Method3()是为了测试自旋锁

参考:

 

Java同步机制总结--synchronized(http://leo-faith.iteye.com/blog/177779)

posted on 2011-07-19 18:09 一叶飘舟 阅读(...) 评论(...) 编辑 收藏