Searches are getting executed out of order

GooglePlacesSearchModel.swift

class GooglePlacesSearchModel {
    static var serialQueue: dispatch_queue_t = dispatch_queue_create("com.example.Search.GooglePlaces", DISPATCH_QUEUE_SERIAL)
[...]
    func executeSearch(searchText: String, mapView: GMSMapView?, completion: ([AnyObject]) -> Void) -> () {
        // get bounds of mapView to weight our autocomplete query accordingly
        var bounds: GMSCoordinateBounds?
        if let visibleRegion = mapView?.projection.visibleRegion() {
            bounds = GMSCoordinateBounds(coordinate: visibleRegion.farLeft, coordinate: visibleRegion.nearRight)
        }
    
        // get centre point of our mapView for use with nearby search
        if let centerCoordinates = getMapViewCenterCoordinate(mapView),
            let radius = getViewRadius(mapView)
            where shouldDoNearbySearch(searchText) {

            dispatch_async(GooglePlacesSearchModel.serialQueue, {
                self.doNearbySearch(searchText, location: centerCoordinates, radius: radius) { (results) in
                    // return [Dictionary<String, AnyObject>]
                    completion(results)
                }
            })
        } else {
            // autocomplete query
            dispatch_async(GooglePlacesSearchModel.serialQueue, {
                self.doAutocompleteQuery(searchText, bounds: bounds) { (results) in
                    // return [GMSAutocompletePrediction]
                    completion(results)
                }
            })
        }
    }
}

SearchController.swift

func updateSearchResultsForSearchController(searchController: UISearchController) {
    if let searchText = searchController.searchBar.text where searchText != "" {
        // retrieve results from Google
        self.googlePlacesSearchModel.executeSearch(searchText, mapView: self.mapView) { (completion) in
            dispatch_async(dispatch_get_main_queue(), {
                self.googlePlacesResults = completion
print("Search text was: \(searchText)")
print(completion)
                let indexSection = NSIndexSet(index: tableSections.googlePlaces)
                self.tableView.reloadData()
                self.tableView.reloadSections(indexSection, withRowAnimation: .Automatic)
            })
        }
    }
}