dispatch_async not working properly in my scenario? Pls help me

i have 10 csv(.csv) files with more records, and these files i m trying to add local DB like SQlte database, and here i used

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
    [[DBManager getSharedInstance] loadCSVData];

    dispatch_async(dispatch_get_main_queue(), ^{
        //Update UI
    });
});
-(void)loadCSVData{

NSLog(@"%lu",(unsigned long)arrDictList.count);


for (int i=0; i<arrDictList.count; i++) {
    NSString *strDictrictName = [NSString stringWithFormat:@"%@",[arrDictList objectAtIndex:i]];
    NSLog(@"%@",strDictrictName);
    NSString *path = [[NSBundle mainBundle] pathForResource:strDictrictName ofType:@"csv"];
    NSString *fileDataString=[NSString stringWithContentsOfFile:path encoding:NSUTF8StringEncoding error:nil];

    NSArray *districtArr=[fileDataString componentsSeparatedByString:@"\n"];
    NSLog(@"%lu",(unsigned long)districtArr.count);
    if(districtArr)
    {
        for(int j=1;j<[districtArr count]-1;j++)
        {
            NSString *StrValue=[NSString stringWithFormat:@"%@",[districtArr objectAtIndex:j]];
            StrValue=[StrValue stringByReplacingOccurrencesOfString:@"\"" withString:@""];
            StrValue=[StrValue stringByReplacingPercentEscapesUsingEncoding:NSUTF8StringEncoding];

            //Here give whatever saperator you need to saperate data
            NSArray *arr=[StrValue componentsSeparatedByString:@","];

            NSString *insertStmt = [NSString stringWithFormat: @"INSERT INTO %@ (id,villiage_name) values(\"%@\",\"%@\")",[arrDictList objectAtIndex:i],[arr objectAtIndex:0],[arr objectAtIndex:1]];

            //Here add logic to insert row in your database table
            [self executeQuery:insertStmt];
        }
    }

}

}

Note: here problem is only first 5 csv file records only added (reading remaining 5 csv files data not reading, its just display null, data correct (like if i used to read single file its fyn to work)) to local DB, remaining 5 showing null. (i think maybe its thread (time delay) issue).