Android 线程和数据库锁定 [英] Android threading and database locking
问题描述
我们使用 AsyncTasks 来访问数据库表和游标.
We are using AsyncTasks to access database tables and cursors.
不幸的是，我们偶尔会看到有关数据库被锁定的异常.
Unfortunately we are seeing occasional exceptions regarding the database being locked.
E/SQLiteOpenHelper(15963): Couldn't open iviewnews.db for writing (will try read-only):
E/SQLiteOpenHelper(15963): android.database.sqlite.SQLiteException: database is locked
E/SQLiteOpenHelper(15963): at android.database.sqlite.SQLiteDatabase.native_setLocale(Native Method)
E/SQLiteOpenHelper(15963): at android.database.sqlite.SQLiteDatabase.setLocale(SQLiteDatabase.java:1637)
E/SQLiteOpenHelper(15963): at android.database.sqlite.SQLiteDatabase.<init>(SQLiteDatabase.java:1587)
E/SQLiteOpenHelper(15963): at android.database.sqlite.SQLiteDatabase.openDatabase(SQLiteDatabase.java:638)
E/SQLiteOpenHelper(15963): at android.database.sqlite.SQLiteDatabase.openOrCreateDatabase(SQLiteDatabase.java:659)
E/SQLiteOpenHelper(15963): at android.database.sqlite.SQLiteDatabase.openOrCreateDatabase(SQLiteDatabase.java:652)
E/SQLiteOpenHelper(15963): at android.app.ApplicationContext.openOrCreateDatabase(ApplicationContext.java:482)
E/SQLiteOpenHelper(15963): at android.content.ContextWrapper.openOrCreateDatabase(ContextWrapper.java:193)
E/SQLiteOpenHelper(15963): at android.database.sqlite.SQLiteOpenHelper.getWritableDatabase(SQLiteOpenHelper.java:98)
E/SQLiteOpenHelper(15963): at android.database.sqlite.SQLiteOpenHelper.getReadableDatabase(SQLiteOpenHelper.java:158)
E/SQLiteOpenHelper(15963): at com.iview.android.widget.IViewNewsTopStoryWidget.initData(IViewNewsTopStoryWidget.java:73)
E/SQLiteOpenHelper(15963): at com.iview.android.widget.IViewNewsTopStoryWidget.updateNewsWidgets(IViewNewsTopStoryWidget.java:121)
E/SQLiteOpenHelper(15963): at com.iview.android.async.GetNewsTask.doInBackground(GetNewsTask.java:338)
E/SQLiteOpenHelper(15963): at com.iview.android.async.GetNewsTask.doInBackground(GetNewsTask.java:1)
E/SQLiteOpenHelper(15963): at android.os.AsyncTask$2.call(AsyncTask.java:185)
E/SQLiteOpenHelper(15963): at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:256)
E/SQLiteOpenHelper(15963): at java.util.concurrent.FutureTask.run(FutureTask.java:122)
E/SQLiteOpenHelper(15963): at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:648)
E/SQLiteOpenHelper(15963): at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:673)
E/SQLiteOpenHelper(15963): at java.lang.Thread.run(Thread.java:1060)
有没有人有一个通用示例，用于说明从不同于读取的线程写入数据库的代码以及我们如何确保线程安全.
Does anybody have a general example for code which writes to a database from a different thread than the one reading and how can we ensure thread safety.
我的一个建议是使用 ContentProvider，因为这将处理来自多个线程的数据库访问.我要看看这个，但这是处理此类问题的推荐方法吗?考虑到我们在谈论前面或后面，它似乎相当重量级.
One suggestion I've had is to use a ContentProvider, as this would handle the access of the database from multiple threads. I am going to look at this, but is this the recommended method of handling such a problem? It seems rather heavyweight considering we're talking about in front or behind.
推荐答案
我解决了这个相同的异常，只是通过确保我的所有数据库打开都关闭，并且(更重要的是)确保这一点，使每个数据库实例的范围本地化仅适用于需要它的方法.ContentProvider 是一个很好的安全类，可以在从多个线程访问数据库时使用，但也要确保您使用了良好的数据库实践:
I solved this same exception just by making sure all my database opens have closes, and (more importantly) to assure this, making the scope of each database instance local ONLY to the method that needs it. ContentProvider is a good, safe class to use when accessing a db from multiple threads, but also make sure you're using good db practices:
- 将数据库实例保持在本地(没有 SQLiteDatabase 类成员！)
- 以打开数据库的相同方法在数据库上调用
close() - 对从数据库中获得的游标调用
close() - 听 LogCat 了解 SQLiteDatabse 可能有的任何投诉
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