Android多线程操作sqlite（Sqlite解决database locked问题）

参考http://blog.csdn.net/sdsxleon/article/details/18259973 很好
https://github.com/2point0/Android-Database-Locking-Collisions-Example 示例
http://www.eoeandroid.com/forum.php?mod=viewthread&tid=333473 http://bbs.51cto.com/thread-990260-1.html
用事务，速度会很会

方案1：

SQLite实质上是将数据写入一个文件，通常情况下，在应用的包名下面都能找到xxx.db的文件，拥有root权限的手机，可以通过adb shell，看到data/data/packagename/databases/xxx.db这样的文件。

我们可以得知SQLite是文件级别的锁：多个线程可以同时读，但是同时只能有一个线程写。Android提供了SqliteOpenHelper类，加入Java的锁机制以便调用。

如果多线程同时读写（这里的指不同的线程用使用的是不同的Helper实例），后面的就会遇到android.database.sqlite.SQLiteException: database is locked这样的异常。
对于这样的问题，解决的办法就是keep single sqlite connection，保持单个SqliteOpenHelper实例，同时对所有数据库操作的方法添加synchronized关键字。

完美解决sqlite的 database locked 或者是 error 5: database locked 问题

/**
* @FileName : DatabaseHelper.java
* @ProjectName : SqlitePractice
* @PakageName : com.sqlitepractice.database
* @Author : Brant
* @CreateDate : 2012-12-16
*/
package com.sqlitepractice.database;

import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.provider.BaseColumns;
import android.util.Log;

/**
* @Module : 隶属模块名
* @Comments : 描述
* @Author : Brant
* @CreateDate : 2012-12-16
* @ModifiedBy : Brant
* @ModifiedDate: 2012-12-16
* @Modified:
* 2012-12-16: 实现基本功能
*/
public class DatabaseHelper extends SQLiteOpenHelper {
public static final String TAG = "DatabaseHelper";
private static final String DB_NAME = "practice.db";
private final static String DB_TABLE_APP = "app";
private static final int DB_VERSION = 1;
private static final String DB_CREATE_TABLE_APP = "CREATE TABLE " + DB_TABLE_APP + "(" + APP_COLUMNS._ID + " INTEGER PRIMARY KEY AUTOINCREMENT," + APP_COLUMNS.PACKAGE_NAME
+ " NTEXT NOT NULL," + APP_COLUMNS.APP_NAME + " NTEXT NOT NULL," + APP_COLUMNS.APP_NAME_PINYIN + " NTEXT,"
+ APP_COLUMNS.CLASS_NAME + " NTEXT NOT NULL);";

private static DatabaseHelper mInstance;

protected DatabaseHelper(Context context) {
super(context, DB_NAME, null, DB_VERSION);
}

public synchronized static DatabaseHelper getInstance(Context context) {
if (mInstance == null) {
mInstance = new DatabaseHelper(context);
}
return mInstance;
}

public synchronized static void destoryInstance() {
if (mInstance != null) {
mInstance.close();
}
}

@Override
public void onCreate(SQLiteDatabase db) {
db.execSQL(DB_CREATE_TABLE_APP);
}

@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
// TODO Auto-generated method stub

}

public synchronized int getCount() {
Log.d(TAG, "getCount");
int count = -1;
Cursor c = getReadableDatabase().query(DB_TABLE_APP, null, null, null, null, null, null);
if (c.moveToFirst()) {
count = c.getCount();
}
c.close();
c = null;
return count;
}

public synchronized void insert(String packageName, String appLabel, String pinyin, String className) {
Log.d(TAG, "insert");
ContentValues values = new ContentValues(4);
values.put(APP_COLUMNS.PACKAGE_NAME, packageName);
values.put(APP_COLUMNS.APP_NAME, appLabel);
values.put(APP_COLUMNS.APP_NAME_PINYIN, pinyin);
values.put(APP_COLUMNS.CLASS_NAME, className);
getWritableDatabase().insert(DB_TABLE_APP, null, values);
}

public static class APP_COLUMNS implements BaseColumns {
public static final String PACKAGE_NAME = "package_name";
public static final String APP_NAME = "app_name";
public static final String APP_NAME_PINYIN = "app_name_pinyin";
public static final String CLASS_NAME = "class_name";

public static final int ID_INDEX = 0;
public static final int PACKAGE_NAME_INDEX = 1;
public static final int APP_NAME_INDEX = 2;
public static final int APP_NAME_PINYIN_INDEX = 3;
public static final int CLASS_NAME_INDEX = 4;
}

}

　　

package com.sqlitepractice;

import java.util.ArrayList;
import java.util.List;

import android.app.Activity;
import android.os.Bundle;
import android.util.Log;
import android.view.Menu;

import com.sqlitepractice.database.DatabaseHelper;

public class MainActivity extends Activity {
private static final String TAG = "MainActivity";
private static int sThreadCounter = 0;

@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
final int threadCount = 8;
final List<Thread> allThreads = new ArrayList<Thread>(threadCount);
DatabaseHelper helper = DatabaseHelper.getInstance(this);
for (int i = 0; i < threadCount; i++) {
allThreads.add(new DbInsertThread(helper, 50, sThreadCounter++));
}
for (int i = 0; i < threadCount; i++) {
allThreads.add(new FastSelectThread(helper, sThreadCounter++, 50));
}

for (Thread thread : allThreads) {
thread.start();
}

// Wait for all threads to complete before running
for (Thread thread : allThreads) {
try {
thread.join();
Log.i(thread.getName(), "collected");
} catch (InterruptedException e) {
Log.e(TAG, "Interrupted", e);
}
}

Log.i(TAG, "All threads finished!");
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
getMenuInflater().inflate(R.menu.activity_main, menu);
return true;
}

class DbInsertThread extends Thread {
private final String TAG = DbInsertThread.class.getSimpleName();

private final DatabaseHelper mDbHelper;
private int mRunCount;

DbInsertThread(DatabaseHelper helper, int runCount, int id) {
setName(String.format("%1$s-%2$d", TAG, id));

mDbHelper = helper;
mRunCount = runCount;
Log.i(getName(), helper.toString());
}

@Override
public void run() {
for (int i = 0; i < mRunCount; i++) {
try {
mDbHelper.insert("com.xx.xxxx", "测试", "ceshi", "MainActivity");
} catch (Exception e) {
Log.e(getName(), "Insert failed!!!, stopping writes", e);
break;
}
}

Log.i(getName(), "finished!");

}
}

class FastSelectThread extends Thread {
private final String TAG = FastSelectThread.class.getSimpleName();

private final DatabaseHelper mHelper;
private final int mCount;

FastSelectThread(DatabaseHelper helper, int id, int selectCount) {
setName(String.format("%1$s-%2$d", TAG, id));

mHelper = helper;
mCount = selectCount > 0 ? selectCount : 50;

Log.i(getName(), helper.toString());
}

@Override
public void run() {
int count = 0;
while (count < mCount) {
mHelper.getCount();

Log.i(getName(), "start wait");
try {
Thread.sleep(200);
} catch (InterruptedException e) {
e.printStackTrace();
}

Log.i(getName(), "end wait");

count++;
}

Log.i(getName(), "finished!");
}
}

}