Unable to get count of items from JSON before setting up Table View Cells

class MasterTableViewController: UITableViewController {

    var customersDictionary: [Dictionary<String, AnyObject>] = []


    override func viewDidLoad() {
        super.viewDidLoad()

        // data 

        let urlPath: String = "myPHPLocation" //this will be changed to the path where service.php lives
        let url: NSURL = NSURL(string: urlPath)!

        // USE NSURLSession API to fetch data

        let configuration = NSURLSessionConfiguration.defaultSessionConfiguration()

        let session = NSURLSession(configuration: configuration)

        // NSURL Request object
        let request = NSURLRequest(URL: url)
        let dataTask = session.dataTaskWithRequest(request) { (data: NSData?, response: NSURLResponse?, error: NSError?) -> Void in

            do {
                let json = try NSJSONSerialization.JSONObjectWithData(data!, options: .AllowFragments)

                if let customers = json["Customers"] as? [[String: AnyObject]] {
                    self.customersDictionary = customers
                    print(self.customersDictionary.count)
                }
            } catch {
                print("error serializing JSON: \(error)")
            }



        }

        dataTask.resume()


    }


    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }

    // MARK: - Table view data source



    override func numberOfSectionsInTableView(tableView: UITableView) -> Int {
        // #warning Incomplete implementation, return the number of sections
        return 1
    }

    override func tableView(tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
        // #warning Incomplete implementation, return the number of rows
        return customersDictionary.count
    }


    override func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
        let cell = tableView.dequeueReusableCellWithIdentifier("reuseIdentifier", forIndexPath: indexPath)


        // Get references to labels of cell

        cell.textLabel?.text = "Test"


        // Configure the cell...

        return cell
    }