What could possibly cause a memory leak in this code? - swift

Question

I've been trying to find out what causes memory leaks, but in Instruments, I am being told that the memory leak happens at seriesDownloadingQueue.addOperation(downloadOperation) and in the class that calls the method getSeries(), which starts the updating process.
I'm completely new to asynchronous programming and memory leaks. I've read some posts on stack overflow about finding and fixing the leaks. I've also read an article from http://www.raywenderlich.com on how to use Instruments. This app is a database preloader. It downloads and processes information. The .sqlite file will be used in a mobile app.
Below is the code which allegedly causes the memory leak. If you need more information, I'll provide it.
import Foundation
import CoreData
class SerieFetcher: NSObject{
dynamic var didGetSeries: Bool = false
static var doneSeries: Int = 0
func getSeries(){
var seriesDownloadingQueue: NSOperationQueue{
let val = NSOperationQueue()
val.maxConcurrentOperationCount = 32
val.name = "Serie Downloading & Processing Queue"
return val
}
var defaultSessionConfiguration:NSURLSessionConfiguration{
let val = NSURLSessionConfiguration.defaultSessionConfiguration()
val.HTTPMaximumConnectionsPerHost = 20
return val
}
let defaultSession: NSURLSession = NSURLSession(configuration: defaultSessionConfiguration,delegate: nil, delegateQueue: seriesDownloadingQueue)
if let countries = fetchCountries(){
for country in countries{
if let url = NSURL(string:(BASE_URL + "series/"+CAT_STAMPS+"producer/\(country.0)")){
let downloadOperation = downloadSeriesOperation(downloadURL: url, countryObjectID: country.1, countryCount: countries.count, defaultSession: defaultSession , completionHandler: { [weak self](didGetSeries) in
if(didGetSeries == true){
self!.didGetSeries = didGetSeries
print("Finished Downloading Series")
}
})
downloadOperation.completionBlock = nil
seriesDownloadingQueue.addOperation(downloadOperation)
}
}
}
}
func fetchCountries() -> [Int: NSManagedObjectID]?{
let fetchRequest = NSFetchRequest(entityName: "Country")
fetchRequest.resultType = .DictionaryResultType
let objectIDDesc = NSExpressionDescription()
objectIDDesc.name = "objectID"
objectIDDesc.expression = NSExpression.expressionForEvaluatedObject()
objectIDDesc.expressionResultType = .ObjectIDAttributeType
fetchRequest.propertiesToFetch = ["countryID",objectIDDesc]
fetchRequest.returnsDistinctResults = true
do{
let results = try managedContext.executeFetchRequest(fetchRequest) as! [NSDictionary]
var countryIDs: [Int: NSManagedObjectID] = [:]
for result in results{
let countryID: Int = result.valueForKey("countryID") as! Int
let objectID: NSManagedObjectID = result.valueForKey("objectID") as! NSManagedObjectID
countryIDs.updateValue(objectID, forKey: countryID)
}
return countryIDs
}catch let error as NSError{
print(error.localizedDescription)
}
return nil
}
}
class downloadSeriesOperation: NSOperation{
let countryObjectID:NSManagedObjectID
let downloadURL:NSURL
let countryCount:Int
let defaultSession:NSURLSession
let completionHandler: (didGetSeries: Bool) -> Void
init(downloadURL:NSURL, countryObjectID: NSManagedObjectID,countryCount: Int, defaultSession:NSURLSession, completionHandler: (didGetSeries:Bool) -> Void){
self.downloadURL = downloadURL
self.countryObjectID = countryObjectID
self.countryCount = countryCount
self.defaultSession = defaultSession
self.completionHandler = completionHandler
}
override func main() {
let dataTask = defaultSession.dataTaskWithURL(downloadURL, completionHandler: { (data, response, error) in
let privateMOC = NSManagedObjectContext(concurrencyType: .PrivateQueueConcurrencyType)
privateMOC.persistentStoreCoordinator = managedContext.persistentStoreCoordinator
privateMOC.undoManager = nil
var parsedData: NSArray?
do{
parsedData = try NSJSONSerialization.JSONObjectWithData(data!, options: NSJSONReadingOptions()) as? NSArray
}catch let error as NSError{
print(error.localizedDescription)
}
for val in parsedData!{
if let serieID = Int(val[0] as! NSString as String){
if let serieName = val[1] as? NSString as? String{
if serieID == 0{
continue
}
let serie = NSEntityDescription.insertNewObjectForEntityForName("Serie", inManagedObjectContext: privateMOC) as! Serie
serie.country = privateMOC.objectWithID(self.countryObjectID) as? Country
serie.serieID = serieID
serie.serieName = serieName
}
}
}
privateMOC.performBlock({
do{
try privateMOC.save()
privateMOC.reset()
}catch let error as NSError{
print(error.localizedDescription)
}
})
SerieFetcher.doneSeries += 1
print(self.countryCount,"/",SerieFetcher.doneSeries)
if(SerieFetcher.doneSeries == self.countryCount){
self.completionHandler(didGetSeries: true)
}
})
dataTask.resume() //Start the Download
}
}