ディスパッチグループが期待通りに動作しない

Question

私はこれと同様の機能をセットアップしても問題ありませんが、ここではgroup.leave()にクラッシュしています。テストでは、print("getRekos processing over, handler is called")の後に1,つまり、group.leave()がforループを完全に完了する前に呼び出されているか、反復のいくつかがグループ外に「漏れている」ということです。これを引き起こす原因は何ですか？私は複数の一致（matches.count > 1が）getExpandedURLsFromTextである場合、結果ハンドラは、あなたのディスパッチグループ・ロジック・ブレークを行う、複数回呼び出されgetRekos

public func getRekos(rekoType: RekoCategory, handler: @escaping (Set<URL>) -> Void) { 

     let setOfLinks = Set<URL>() 
     let group = DispatchGroup() //Dispatch group code from: http://stackoverflow.com/questions/38552180/dispatch-group-cannot-notify-to-main-thread 
     let backgroundQ = DispatchQueue.global(qos: .default) 


     TwitterRequest().fetchTweets(searchType: rekoType) { result in 

      guard let tweets = TWTRTweet.tweets(withJSONArray: result) as? [TWTRTweet] else { print("error in getRekos casting TwitterRequest().fetchTweets result as [TWTRTweet]"); return } 

      for tweet in tweets { 

       let text = tweet.text 

       group.enter() 
       backgroundQ.async(group: group, execute: { 

        //Check tweet text if contains any URLs 
        self.getExpandedURLsFromText(text: text, handler: { (getExpandedLinksResult, error) in 

         if error != nil { 
          group.leave() 
         } else { 

          for link in getExpandedLinksResult { 
           print("link = \(link)") 

          } 
          group.leave() 
         } 
        }) 
       }) 
      } //for tweet in tweets loop 
      group.notify(queue: backgroundQ, execute: { 
       DispatchQueue.main.async { 
        print("getRekos processing over, handler is called") 
        handler(setOfLinks) 
       } 
      }) 
     } 
    } 


private func getExpandedURLsFromText(text: String, handler: @escaping ([URL], Error?) -> Void) { 

    var linksInText = [URL]() 
    let group = DispatchGroup() //Dispatch group code from: http://stackoverflow.com/questions/38552180/dispatch-group-cannot-notify-to-main-thread 
    let backgroundQ = DispatchQueue.global(qos: .default) 


    let types: NSTextCheckingResult.CheckingType = .link 
    let detector = try? NSDataDetector(types: types.rawValue) 

    guard let detect = detector else { print("NSDataDetector error"); return } 

    let matches = detect.matches(in: text, options: .reportCompletion, range: NSMakeRange(0, (text.characters.count))) 

    //CRITICAL CHECK - results were getting lost here, so pass back error if no match found 
    if matches.count == 0 { 
     handler([], RekoError.FoundNil("no matches")) 
    } 
     // Iterate through urls found in tweets 
     for match in matches { 

      if let url = match.url { 

        guard let unwrappedNSURL = NSURL(string: url.absoluteString) else {print("error converting url to NSURL");continue} 

        group.enter() 
        backgroundQ.async(group: group, execute: { 

         //Show the original URL (ASYNC) 
         unwrappedNSURL.resolveWithCompletionHandler(completion: { (resultFromResolveWithCompletionHandler) in 

          guard let expandedURL = URL(string: "\(resultFromResolveWithCompletionHandler)") else {print("couldn't covert to expandedURL"); return} 

          linksInText.append(expandedURL) 
          group.leave() 
          //handler(linksInText, nil) 
         }) 
        }) 


      } else { print("error with match.url") } 
     } //for match in matches loop 
      group.notify(queue: backgroundQ, execute: { 
       DispatchQueue.main.async { 
        //print("getExpandedURLsFromText processing over, handler is called") 
        handler(linksInText, nil) 
       } 
      }) 
} 

// Create an extension to NSURL that will resolve a shortened URL 
extension NSURL 
{ 
    func resolveWithCompletionHandler(completion: @escaping (NSURL) -> Void) { 
     let originalURL = self 
     let req = NSMutableURLRequest(url: originalURL as URL) 
     req.httpMethod = "HEAD" 

     URLSession.shared.dataTask(with: req as URLRequest){body, response, error in 

      if error != nil { 
       print("resolveWithCompletionHandler error = \(error)") 
      } 

      if response == nil { 
       print("resolveWithCompletionHandler response = nil") 
      } 
      completion(response?.url as NSURL? ?? originalURL) 
      } 
      .resume() 
    } 
} 

Answer 1

内部で使用されているgetExpandedURLためのコードと私のカスタム拡張resolveWithCompletionHandlerを掲載しましたアップ。

ロジックをクリーンアップします。

完了ハンドラは、正常終了時に常に1回、エラーごとに1回だけ呼び出されるようにする必要があります。 guardステートメントの複数の場所で完了ハンドラへの呼び出しがありません。