a little preface: If i create a simple activity, with strict mode enabled, and i keep changing orientation i notice some warning like "InstanceCountViolation;instances=2;limit=1"
If i understand correctly this is perfectly normal because the old activity isn't GCed instantly, for example if i add an explicit GC on each orientation change the warning disappear
Is that correct?

I have noticed that the main activity of my application is showing the same warning but with "instances=3", in this case if i add an explicit GC on each orientation change the warning will still show up but with "instances=2"
This means that there is some leak that i have to avoid? Or even in this case can be normal and is caused by something like loaders and other things?

I want to encrypt some files with AES, i have first tried CipherInputStream/CipherOutputStream but they are slow and cause a lot of GC. 
Now i'm using a JNI wrapper that uses openssl to encrypt and decrypt with some java callback for progress (one per percentage point).
Do you have some suggestions to further improve this or any better alternatives?

I have a singleton class that has the purpose to be the "datamanager", internally it instantiate a global SQLiteOpenHelper 
On every method where i need to interact with the database i'm calling something like "helper.getWritableDatabase().query". 
Do i need to ensure that the SQLiteDatabase is closed with a try/finally in every method?
In alternative can i use directly a global SQLiteDatabase initialized with "helper.getWritableDatabase" when the "datamanager" singleton is created or is a bad approach?