SQLiteOpenHelper getWritableDatabse() fails with n

问题:

I have a very strange problem. It only shows from time to time, on several devices. Can't seem to reproduce it when I want, but had it so many times, that I think I know where I get it.

So I have a Loader which connects to sqlite through a singleton SQLiteOpenHelper:

try {
    Log.i(TAG, "Get details offline / db helper: "+DatabaseHelper.getInstance(getContext()));
    SQLiteDatabase db=DatabaseHelper.getInstance(this.getContext()).getWritableDatabase();
    Log.i(TAG, "Get details offline / db: "+db);
    //doing some work on the db...
} catch(SQLiteException e){
    e.printStackTrace();
    return null;
} catch(Exception e){
    e.printStackTrace();
    return null;
    //trying everything to grab some exception or whatever
}

My SQLIteOpenHelper looks something like this:

public class DatabaseHelper extends SQLiteOpenHelper { 

    private static DatabaseHelper mInstance = null;
    private static Context mCxt;

    public static DatabaseHelper getInstance(Context cxt) {
        //using app context as suggested by CommonsWare
        Log.i("DBHELPER1", "cxt"+mCxt+" / instance: "+mInstance);
        if (mInstance == null) {
            mInstance = new DatabaseHelper(cxt.getApplicationContext());
        }
        Log.i("DBHELPER2", "cxt"+mCxt+" / instance: "+mInstance);
        mCxt = cxt;
        return mInstance;
    }

    //private constructor
    private DatabaseHelper(Context context) {
        super(context, DATABASE_NAME, null, DATABASE_VERSION);
        this.mCxt = context;
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        //some tables created here
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        //upgrade code here
    }
}

It really works great in most cases. But from time to time I get a log similar to this:

06-10 23:49:59.621: I/DBHELPER1(26499): cxtcom.myapp@407152c8 / instance: com.myapp.helpers.DatabaseHelper@40827560
06-10 23:49:59.631: I/DBHELPER2(26499): cxtcom.myapp@407152c8 / instance: com.myapp.helpers.DatabaseHelper@40827560
06-10 23:49:59.631: I/DetailsLoader(26499): Get event details offline / db helper: com.myapp.helpers.DatabaseHelper@40827560
06-10 23:49:59.631: I/DBHELPER1(26499): cxtcom.myapp@407152c8 / instance: com.myapp.helpers.DatabaseHelper@40827560
06-10 23:49:59.651: I/DBHELPER2(26499): cxtcom.myapp@407152c8 / instance: com.myapp.helpers.DatabaseHelper@40827560

This line Log.i(TAG, "Get details offline / db: "+db); never gets called! No Exceptions, silence. Plus, the thread with the Loader is not running anymore.

So nothing past the line:

SQLiteDatabase db=DatabaseHelper.getInstance(this.getContext()).getWritableDatabase(); 

gets executed.

What can possibly go wrong on this line?