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!");
		}
	}

}