multithreading - sqlite and threading with iPhone SDK -

i have iphone app using sqlite 3.6 (not fmdb) store , load data. load database when app loads , uses same database connection through whole app.

in background thread app downloads data webserver , writes database. @ same time main thread might need write same database. leads exc_bad_access both threads trying access database.

what best , easiest way able use database different threads?

this example shows problem:

sqlite3 *database;     - (bool)application:(uiapplication *)application didfinishlaunchingwithoptions:(nsdictionary *)launchoptions {         nsarray *paths = nssearchpathfordirectoriesindomains(nsdocumentdirectory, nsuserdomainmask, yes);     nsstring *documentsdirectory = [paths objectatindex:0];     nsstring *path = [documentsdirectory stringbyappendingpathcomponent:@"database.db"];      if (sqlite3_open([path utf8string], &database) != sqlite_ok) {         sqlite3_close(database);         return yes;     }      [nsthread detachnewthreadselector:@selector(test) totarget:self withobject:nil];     [self test];     return yes; }  -(void)test {     (int = 0; < 2000; i++) {         nslog(@"%i",i);         sqlite3_exec([self getdb],"update mytable set test=''", 0, 0, 0);     } } 

edit:

after willcodejavaforfood's answer below i've tried change code use separate database object (connection) each separate thread , added sqlite3_busy_timeout() sqlite retry write if database busy. don't exc_bad_access anymore i've noticed not data inserted. not stable solution either. seems hard sqlite working threading..

my new solution separate connections:

-(void)test {     sqlite3 *db = [self getnewdb];     (int = 0; < 2000; i++) {         nslog(@"%i",i);         sqlite3_exec(db,"update mytable set test=''", 0, 0, 0);     } }  - (sqlite3 *)getnewdb {     sqlite3 *newdb = nil;     if (sqlite3_open([[self getdbpath] utf8string], &newdb) == sqlite_ok) {         sqlite3_busy_timeout(newdb, 1000);     } else {         sqlite3_close(newdb);     }     return newdb; } 

i solved problem using 1 thread , nsoperationqueue insert data. give thought. i've never been able stable system mutliple threads, , writes aren't important queuing helps.

as per request, more infos:

i have subclass of nsoperation instantiate model object want store. these operations submitted extension of nsoperationsqueue runs in seperate thread. custom queue adds pointer database instance. when operation executed, uses [nsoperationsqueue currentqueue] property access queue , database. on purpose, used non-concurrent operations (maxoperations set 1)
hence, 1 query (or update) executed @ time consecutivly, in background.

obviously need kind of callback after you're finished.

it possibly not fast, stable , cleanest solution find.

docs:
http://developer.apple.com/library/ios/documentation/general/conceptual/concurrencyprogrammingguide/operationobjects/operationobjects.html
http://www.cimgf.com/2008/02/16/cocoa-tutorial-nsoperation-and-nsoperationqueue/
http://icodeblog.com/2010/03/04/iphone-coding-turbo-charging-your-apps-with-nsoperation/