sqlite access from multiple threads for reading

there are similar questions but not clear answer around using sqlite db from multiple threads. Consider the following scenario:

class MainActivity extends Activity {
DbHelper db; //extends sqliteopenhelper
...
void M1() {
    db.getReadableDatabase();
    Cursor c = db.query("...."
    ...
    db.close();
}

void M1() {
    db.getReadableDatabase();
    Cursor c = db.query("...."
    ...
    db.close();
}

ok, this is not multi-thread but question is that,

1. does it become a problem to use the same instance of sqliteopenhelper instance (i.e. db) like above, opening and closing in many times in different methods?

   And my scenario is the following:

   myAsync extends AsyncTask
   doInBackground(.. {
   
      do something using M1();  //this is a background thread
   }}         
   
   onResume()...{
       myAsync.execute();
       M2();      //this is the main thread
      ...
     }
   

2. if you see that 开发者_如何学编程in the async scenario, it is probably that two method can access the same database at the same time(for reading only- how about writing?). But they are using the same instance of SqliteOpenHelper. Would it cause to collision and if so how to avoid this?

3. I would like to learn more about sqlite database and concurrency

   Any ideas would be greatfully appreciated.

ya there is a chance of not collision but your db may close when another thread is aquired, you can go for "Synchronized" concept of thread ie priority and etc when we use synchronized keyword then, one thread completes it task then other thread will starts