Java SQLiteDatabase多线程锁定模式
我使用这个类来管理到底层SQLiteDatabase的连接Java SQLiteDatabase多线程锁定模式,java,android,multithreading,sqlite,singleton,Java,Android,Multithreading,Sqlite,Singleton,我使用这个类来管理到底层SQLiteDatabase的连接 public class BasicDataSource { protected DatabaseHandler dbHelper; protected volatile SQLiteDatabase readable_database; protected volatile SQLiteDatabase writable_database; protected Object read_lock = n
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,另一个用于写入。
但我还是偶尔会遇到这样的例外:
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,当试图在getWritableDatabase中获得锁时,数据库以某种方式被锁定
我的SQLiteOpenHelper是单例模式,数据源只使用BasicDataSource作为父类
在显示的代码中,我可以做哪些改进来避免SQLiteDatabaseLockedException?在SQLite中,可以有任意多个读卡器,但任何编写器都会阻止所有其他读卡器和编写器 您必须为读卡器和写卡器使用一个锁 请注意,只要您实际访问数据库,就必须保持锁
如果要支持多个读卡器,请使用实现的锁,例如。大概是这样的:
在多线程概念中,如果我有多个线程使用这种R/W锁定模式,那么并发读/写将不会被处理,不是吗?我的意思是,当两个数据源从两个线程写入时,这个锁将只对每个单独的DS有效…锁的目的是协调多个线程。因此,所有线程都将共享同一个锁(在本例中为
MyData
类)。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,为什么要使用Lock类而不是synchronized java关键字?SQLite有锁,但没有同步,即在锁冲突中,它只是等待随机时间并重试。读写器锁允许同时多个读写器。@CL.您建议的解决方案允许跨R/W操作同步。如何修复多线程同时写入操作的问题。你能推荐一下吗?
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();
}
}
}