SQLiteDatabase multi-thread locking pattern
In SQLite, there can be arbitrarily many readers, but any writer blocks all other readers and writers.
You have to use a single lock for both readers and writers.
Please note that locks must be held as long as you're actually accessing the database.
If you want to support multiple readers, use a lock that implements ReadWriteLock, such as ReentrantReadWriteLock. Something like this:
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(); } }}