query database asynchornously

database.m

- (void)query:(NSString *)query completion:(CompletionCallback)completion {
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^ {
        
        while(isBusy) {
            // wait for it
            // or should I say, sleep?
        }
        
        isBusy = YES;
        
        sqlite3_stmt *statement;
        int prepareCode = sqlite3_prepare_v2(database, [query UTF8String], -1, &statement, NULL);
        if (prepareCode != SQLITE_OK) {
            NSString *error = [NSString stringWithFormat:@"%s", sqlite3_errmsg(database)];
            completion(nil, error);
            return;
        }
        
        int columnCount = sqlite3_column_count(statement);
        
        NSMutableArray *result = [NSMutableArray new];
        while (sqlite3_step(statement) == SQLITE_ROW) {
            NSDictionary *row = [self bundle: statement columnCount: columnCount];
            [result addObject:row];
        }
        
        sqlite3_finalize(statement);
        
        int errorCode = sqlite3_errcode(database);
        NSString *errMsg = (errorCode == SQLITE_OK) ? nil : [NSString stringWithFormat:@"%s", sqlite3_errmsg(database)];
        
        completion(result, errMsg);
        
        isBusy = NO;
    });
}