I have a location-based app that gets location every 1 second, and saves a batch of the locations at a time to the CoreData DB so as not to make the locations array too large. However, for some reason it crashes with EXC_BAD_ACCESS even though I use dispatch_async on a SERIAL QUEUE:
Created a global serial custom queue like this:
var MyCustomQueue : dispatch_queue_t =
dispatch_queue_create("uniqueID.for.custom.queue", DISPATCH_QUEUE_SERIAL);
in the didUpdateToLocation protocol function, I have this bit of code that saves the latest batch of CLLocation items onto the disk, if the batch size is greater than a preset number:
if(myLocations.count == MAX_LOCATIONS_BUFFER)
{
dispatch_async(MyCustomQueue)
{
for myLocation in self.myLocations
{
// the next line is where it crashes with EXC_BAD_ACCESS
newLocation = NSEntityDescription.insertNewObjectForEntityForName(locationEntityName, inManagedObjectContext: context as NSManagedObjectContext) ;
newLocation.setValue(..)
// all the code to set the attributes
}
appDelegate.saveContext();
dispatch_async(dispatch_get_main_queue()) {
// once the latest batch is saved, empty the in-memory array
self.myLocations = [];
}
}
}
The mystery is, isn't a SERIAL QUEUE supposed to execute all the items on it in order, even though you use dispatch_async (which simply makes the execution concurrent with the MAIN thread, that doesn't touch the SQLite data)?
Notes:
- The crash happens at random times...sometimes it'll crash after 0.5 miles, other times after 2 miles, etc.
- If I just take out any of the dispatch_async code (just make everything executed in order on the main thread), there is no issue.
