Question

I’m developing an application that uses SQLite as the primary data storage method. I have two processes running for my app using an alternate entry point.

I need to access the same DB from the two different processes but as we all now SQLite is not like a server DB engine, it can only be accessed once at a time.

I wanted to know if there is a way to kind of “lock” the DB when it’s being accessed by other process so that if the second process tries to acces the DB at the same time, it would wait until the first process finishes and then try to access it again.

How can this issue be treated?

Answer 1

If you have not already, create a class that abstracts your database access out and store it in the RuntimeStore. From wherever you are going to interface with SQLite, get a reference to that class using the GUID you stored it with (RuntimeStore.get(long)) and synchronize the class however you would normally (member object lock, synchronized methods).

Do NOT just use the Wikipedia style singleton pattern as it is not a true singleton across processes on this platform.

See:

http://www.blackberry.com/developers/docs/5.0.0api/net/rim/device/api/system/RuntimeStore.html

Sample:

class SQLManager {
    private static long GUID = 0xa178d3ce564cae69L; // hash of com.stackoverflow.SQLManager

    private SQLManager() {
        // ctor stuff here
    }

    public static SQLManager getInstance() {
        RuntimeStore rs = RuntimeStore.getRuntimeStore();

        SQLManager instance = rs.get(GUID);

        if (instance == null) {
            instance = new SQLManager();
            rs.put(GUID, instance);
        }

        return instance;
    }
}

You’re still using the singleton “pattern” per se, but you’re storing the object instance in the RuntimeStore on first getInstance call, and subsequently pulling it form the RuntimeStore – using a GUID that you specify.