android - SQLite and multi threading - DROP TABLE IS EXISTS -

i have application syncronize data between sql server , sqlite...

i'm using mutithreading update few tables concurrently.....

i'm trying follow below:

            // drop table if exists before insert data             dbhelper.droptable(schema.gettable());              // create new table             dbhelper.createtable(schema);              // begin transaction             dbhelper.opentransaction();                              //while() { inserts }               // end transaction             dbhelper.endtransaction(); 

i'm using same dbhelper instance threads.... first thread executes pretty well, seconds crashing on "droptable()", 's wrong approach?

this how pass dbhelper threads:

    dbhelper dbhelper = new dbhelper(getactivity());     int max = mrequestlist.size();     (int row = 0; row < max; row++) {         datareaderrequest request = mrequestlist.get(row);         dataupdatetask task = dataupdatemanager.startupdate(dbhelper,                 request);     } 

tks.