完成后停止功能

Question

我有一个函数，在我调用它之后，它会不断地调用函数（一旦for循环完成了stocks.count，函数将从0重新开始，以无限循环到达stocks.count并访问http，导致http在几分钟后停止响应，然后崩溃应用程序。我已经尝试添加一个计时器，甚至在执行一个函数后执行一个segue（它改变了页面，但函数仍然在调用http）。但没有什么能使功能停止。我很感激任何帮助，因为这个问题在3周内被困在这个问题上:(

我按如下方式调用该函数：

self.downloadStockPrice({ () -> () in
            }, stocks: stocks)

这就是功能本身：

func downloadStockPrice(completed: DownloadComplete, stocks: [Stock]) {

        for x in 0 ..< stocks.count {
            let stock = stocks[x].stock
            let requestURL: NSURL = NSURL(string: "http://query.yahooapis.com/v1/public/yql?q=select%20*%20from%20yahoo.finance.quotes%20where%20symbol%20in%20(%22\(stock)%22)&env=store%3A%2F%2Fdatatables.org%2Falltableswithkeys&format=json")!
            let urlRequest: NSMutableURLRequest = NSMutableURLRequest(URL: requestURL)
            let session = NSURLSession.sharedSession()
            let task = session.dataTaskWithRequest(urlRequest) {
                (data, response, error) -> Void in

                let httpResponse = response as! NSHTTPURLResponse
                let statusCode = httpResponse.statusCode

                if (statusCode == 200) {
                    print("Everyone is fine, file downloaded successfully.")

                    do{

                        let json = try NSJSONSerialization.JSONObjectWithData(data!, options:.AllowFragments)
                        if let queryDict = json["query"] as? Dictionary<String, AnyObject> {
                            if let resultsDict = queryDict["results"] as? Dictionary<String, AnyObject> {
                                if let quoteDict = resultsDict["quote"] as? Dictionary<String, AnyObject> {
                                    let bidString = quoteDict["Bid"] as? String
                                    DataService.ds.REF_BASE.child("stocks").child(stock).child("lastPrice").setValue(Float(bidString!))
                                }
                            }
                        }

                    }catch {
                        print("Error with Json: \(error)")
                    }

                }
            }

            task.resume()
        }
    }