我使用这个类来管理与底层sqlite
Database的连接
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();
}
}
它包含两个锁,一个用于读取,第二个用于写入.
但我还是偶尔得到这样的例外：
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,当尝试在getWritableDatabase中获取锁定时,数据库被某种方式锁定.
解决方法
在sqlite中,可以有任意多的读者,但任何作家都会阻止所有其他读者和作家.
您必须为读者和作家使用单一的锁.
请注意,只要您实际访问数据库,锁必须保持.
如果要支持多个读取器,请使用实现ReadWriteLock的锁,例如ReentrantReadWriteLock.这样的东西：
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();
}
}
}
