SQLiteDatabase多线程锁定模式

我使用这个类来管理连接到底层SQLiteDatabaseSQLiteDatabase多线程锁定模式

public class BasicDataSource { 

    protected DatabaseHandler dbHelper; 
    protected volatile SQLiteDatabase readable_database; 
    protected volatile SQLiteDatabase writable_database; 
    protected Object read_lock = new Object(); 
    protected Object write_lock = new Object(); 
    protected Context context; 

    protected BasicDataSource(Context ctx) { 
     dbHelper = DatabaseHandler.getInstance(ctx); 
     getReadableDatabase(); 
     dbHelper.onCreate(getWritableDatabase()); 
     this.context = ctx; 
    } 

    public synchronized void close() { 
     dbHelper.close(); 
    } 

    protected void closeInsertHelpers(InsertHelper... helpers) { 
     for (InsertHelper ih : helpers) { 
      if (ih != null) 
       ih.close(); 
     } 
    } 

    protected SQLiteDatabase getReadableDatabase() { 
     synchronized (read_lock) { 
      if (readable_database == null || !readable_database.isOpen()) { 
       readable_database = dbHelper.getReadableDatabase(); 
      } 
      return readable_database; 
     } 
    } 

    protected SQLiteDatabase getWritableDatabase() { 
     synchronized (write_lock) { 
      if (writable_database == null || !writable_database.isOpen()) { 
       writable_database = dbHelper.getWritableDatabase(); 
      } 
      return writable_database; 
     } 
    } 

    protected synchronized void open() throws SQLException { 
     getReadableDatabase(); 
     getWritableDatabase(); 
    } 
}

它包含了两个锁，一个用于读取，第二次写。但我还是偶尔会收到这种异常：

java.lang.RuntimeException: An error occured while executing doInBackground() 
     at android.os.AsyncTask$3.done(AsyncTask.java:299) 
     at java.util.concurrent.FutureTask$Sync.innerSetException(FutureTask.java:273) 
     at java.util.concurrent.FutureTask.setException(FutureTask.java:124) 
     at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:307) 
     at java.util.concurrent.FutureTask.run(FutureTask.java:137) 
     at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1076) 
     at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:569) 
     at java.lang.Thread.run(Thread.java:856) 
Caused by: android.database.sqlite.SQLiteDatabaseLockedException: database is locked (code 5): , while compiling: PRAGMA journal_mode 
     at android.database.sqlite.SQLiteConnection.nativePrepareStatement(Native Method) 
     at android.database.sqlite.SQLiteConnection.acquirePreparedStatement(SQLiteConnection.java:882) 
     at android.database.sqlite.SQLiteConnection.executeForString(SQLiteConnection.java:627) 
     at android.database.sqlite.SQLiteConnection.setJournalMode(SQLiteConnection.java:313) 
     at android.database.sqlite.SQLiteConnection.setWalModeFromConfiguration(SQLiteConnection.java:287) 
     at android.database.sqlite.SQLiteConnection.open(SQLiteConnection.java:215) 
     at android.database.sqlite.SQLiteConnection.open(SQLiteConnection.java:193) 
     at android.database.sqlite.SQLiteConnectionPool.openConnectionLocked(SQLiteConnectionPool.java:463) 
     at android.database.sqlite.SQLiteConnectionPool.open(SQLiteConnectionPool.java:185) 
     at android.database.sqlite.SQLiteConnectionPool.open(SQLiteConnectionPool.java:177) 
     at android.database.sqlite.SQLiteDatabase.openInner(SQLiteDatabase.java:804) 
     at android.database.sqlite.SQLiteDatabase.open(SQLiteDatabase.java:789) 
     at android.database.sqlite.SQLiteDatabase.openDatabase(SQLiteDatabase.java:694) 
     at android.app.ContextImpl.openOrCreateDatabase(ContextImpl.java:804) 
     at android.content.ContextWrapper.openOrCreateDatabase(ContextWrapper.java:221) 
     at android.database.sqlite.SQLiteOpenHelper.getDatabaseLocked(SQLiteOpenHelper.java:224) 
     at android.database.sqlite.SQLiteOpenHelper.getWritableDatabase(SQLiteOpenHelper.java:164) 
     at com.mycompany.myapplication.sql.BasicDataSource.getWritableDatabase(BasicDataSource.java:57) 
     at com.mycompany.myapplication.sql.datasources.SomeDataSource.fillUpDatabaseMethod(SomeDataSource.java:264) 
     at com.mycompany.myapplication.sql.datasources.SomeDataSource.renewCacheMethod(SomeDataSource.java:560) 
     at com.mycompany.myapplication.activities.lists.ListsActivity$Worker.doInBackground(ListsActivity.java:315) 
     at com.mycompany.myapplication.activities.lists.ListsActivity$Worker.doInBackground(ListsActivity.java:1) 
     at android.os.AsyncTask$2.call(AsyncTask.java:287) 
     at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:305) 
     ... 4 more 
android.database.sqlite.SQLiteDatabaseLockedException: database is locked (code 5): , while compiling: PRAGMA journal_mode 
     at android.database.sqlite.SQLiteConnection.nativePrepareStatement(Native Method) 
     at android.database.sqlite.SQLiteConnection.acquirePreparedStatement(SQLiteConnection.java:882) 
     at android.database.sqlite.SQLiteConnection.executeForString(SQLiteConnection.java:627) 
     at android.database.sqlite.SQLiteConnection.setJournalMode(SQLiteConnection.java:313) 
     at android.database.sqlite.SQLiteConnection.setWalModeFromConfiguration(SQLiteConnection.java:287) 
     at android.database.sqlite.SQLiteConnection.open(SQLiteConnection.java:215) 
     at android.database.sqlite.SQLiteConnection.open(SQLiteConnection.java:193) 
     at android.database.sqlite.SQLiteConnectionPool.openConnectionLocked(SQLiteConnectionPool.java:463) 
     at android.database.sqlite.SQLiteConnectionPool.open(SQLiteConnectionPool.java:185) 
     at android.database.sqlite.SQLiteConnectionPool.open(SQLiteConnectionPool.java:177) 
     at android.database.sqlite.SQLiteDatabase.openInner(SQLiteDatabase.java:804) 
     at android.database.sqlite.SQLiteDatabase.open(SQLiteDatabase.java:789) 
     at android.database.sqlite.SQLiteDatabase.openDatabase(SQLiteDatabase.java:694) 
     at android.app.ContextImpl.openOrCreateDatabase(ContextImpl.java:804) 
     at android.content.ContextWrapper.openOrCreateDatabase(ContextWrapper.java:221) 
     at android.database.sqlite.SQLiteOpenHelper.getDatabaseLocked(SQLiteOpenHelper.java:224) 
     at android.database.sqlite.SQLiteOpenHelper.getWritableDatabase(SQLiteOpenHelper.java:164) 
     at com.mycompany.myapplication.sql.BasicDataSource.getWritableDatabase(BasicDataSource.java:57) 
     at com.mycompany.myapplication.sql.datasources.SomeDataSource.fillUpDatabaseMethod(SomeDataSource.java:264) 
     at com.mycompany.myapplication.sql.datasources.SomeDataSource.renewCacheMethod(SomeDataSource.java:560) 
     at com.mycompany.myapplication.activities.lists.ListsActivity$Worker.doInBackground(ListsActivity.java:315) 
     at com.mycompany.myapplication.activities.lists.ListsActivity$Worker.doInBackground(ListsActivity.java:1) 
     at android.os.AsyncTask$2.call(AsyncTask.java:287) 
     at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:305) 
     at java.util.concurrent.FutureTask.run(FutureTask.java:137) 
     at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1076) 
     at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:569) 
     at java.lang.Thread.run(Thread.java:856)

这意味着，试图getWritableDatabase将收购锁当数据库被莫名其妙地锁定。

我的SQLiteOpenHelper是单例模式，DataSources仅使用BasicDataSource作为父类。

我可以做些什么来改进显示代码中的SQLiteDatabaseLockedException？

来源

2012-10-06 Marek Sebera

在SQLite中，可以有任意多个读者，但任何作者都会阻止所有其他读者和作者。

您必须为读者和作者使用单个锁。

请注意，只要您实际访问数据库，就必须锁定锁定。

如果你想支持多个阅读器，使用实现ReadWriteLock锁，如ReentrantReadWriteLock。事情是这样的：

class MyData { 
    private final ReentrantReadWriteLock rwl = new ReentrantReadWriteLock(); 
    private final Lock r = rwl.readLock(); 
    private final Lock w = rwl.writeLock(); 

    public Data ReadSomething(int id) { 
     r.lock(); 
     try { 
      Cursor c = readableDatabase.query(...); 
      return c.getString(0); 
     } finally { 
      r.unlock(); 
     } 
    } 

    public void ChangeSomething(int id, int value) { 
     w.lock(); 
     try { 
      writeableDatabase.update(...); 
     } finally { 
      w.unlock(); 
     } 
    } 
}

来源

2012-10-06 09:57:20

在多线程的概念，如果非要用这个R/W锁定模式多线程/写不会被处理的并发读书，不是吗？我的意思是，当两个DataSources从两个线程写入时，此锁定将仅对每个DS有效... –

锁定的目的是协调多个线程。所以所有的线程都会共享相同的锁（在这个例子中，MyData类）。 –

我觉得不需要锁，因为SQLiteDatabase在内部处理锁定。我复杂的多线程应用程序不需要任何你描述的机制。写入锁定由SQLiteDatabase.beginTransaction/endTransaction处理。另外，为什么使用Lock类而不是同步java关键字？ –

SQLiteDatabase多线程锁定模式

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