ReloadData within NSURLSession not updating table

I am trying to reload table data from a NSURLSession using the following function in Swift, but can't get it to reload into the table. All I want to do is update table with JSON data. Can get it to print on console but not update table.

  func get_data_from_url(url:String)

{

    let urlPath = url
    guard let endpoint = NSURL(string: urlPath) else { print("Error creating endpoint");retu }
    let request = NSMutableURLRequest(URL:endpoint)
    NSURLSession.sharedSession().dataTaskWithRequest(request) { (data, response, error) -> Void in
        do {
            guard let dat = data else { throw JSONError.NoData }
            guard let json = try NSJSONSerialization.JSONObjectWithData(dat, options: []) as? Dictionary<String, Array<Dictionary<String,String>>> else { throw JSONError.ConversionFailed }

            self.myDictionary = json
            let newItem = Video(name: "Bob", imageURL: "")
            ItemModel.sharedInstance.categories[0].videos.append(newItem)

           print ("New item:      ",ItemModel.sharedInstance.categories[0].videos)

          // ALL okay above the new item is displayed in the console.
          // Also can add static item below resume() and this is successfully loaded onto table. Items within the NSURLSession function are not updated.

          // I would expect reloadData() to work here but it is not. 
          self.tableView.reloadData()


        } catch let error as JSONError {
            print(error.rawValue)
        } catch {
            print(error)
        }

        }.resume()

       //This works outside NSURLSession function.
       let newItem = Video(name: "Jim", imageURL: "")
       ItemModel.sharedInstance.categories[0].videos.append(newItem)

Any help our guidance would be greatly appreciated.