Using Core Data to save background location updates - multithreading

Question

I am trying to set up an app so that there is a background task where the locationManager receives updates that are then stored using Core Data. Here is the code I am using to run the locationManager as a background task:
(void)viewDidLoad
{
[super viewDidLoad];
timerAndMap = [[UIApplication sharedApplication] beginBackgroundTaskWithExpirationHandler:^{
[self endDate];
}];
if(nil == locationManager) {
locationManager = [[CLLocationManager alloc] init];
}
locationManager.delegate = self;
locationManager.distanceFilter = 500;
locationManager.desiredAccuracy = kCLLocationAccuracyBest;
[locationManager startUpdatingLocation];
[[UIApplication sharedApplication] endBackgroundTask:timerAndMap];
}
However, the problem I am having is figuring out how to make the delegate methods part of the background thread. When the locationManager calls didUpdateToLocation I want to save the longitude, latitude, and date of the new location as attributes of an entity in a temporary managedObjectContext that is then merged with my established ManagedObjectContext on the main thread (as to my understanding while the app is running in the background new Core Data entities cannot be stored to my main thread ManagedObjectContext).

Answer 1

Locations are updated every second or so, create a NSMutableArray with the coordinates, keep a list of the coordinates, and when it reaches a point, create an NSArray with the coordinates from the mutable array, clear the NSMutableArray, pass the NSArray instance to the background thread, and perform the save.
Edit: based on the new information: CLLocationManager's method are asynchronous. What you can do is, if this is what you are trying to accomplish, to dispatch a background block and create your entity within the block on your delegate callback. You can even manage your own own serial dispatch_queue to do this.
Take into consideration thou, that just because you are doing something it the background that does not make it efficient. You will still be calling save every time you get a new location (which could be every 1-2 seconds). Writing into the persistent store is expensive.