Swiftでカスタム補完ブロックを作成する方法

Question

私は後処理をやろうとしています

a。私の非同期機能の1つが終了したら

b。一度すべての私の非同期機能が終了した。

残念ながら、私は以下のコードで競合状態に陥ります。

func foo(stuff: AnArrayOfObjects, completed: (NSError?)->()) { 
    // STEP 1 OF CREATING AN OVERALL COMPLETION BLOCK: Create a dispatch group. 
    let loadServiceGroup: dispatch_group_t = dispatch_group_create() 

    // Define errors to be processed when everything is complete. 
    // One error per service; in this example we'll have two 
    let configError: NSError? = nil 
    let preferenceError: NSError? = nil 

    // some more preprocessing/variable declarations here. E.g.: 
    var counter = 0 

    // STEP 2 OF CREATING AN OVERALL COMPLETION BLOCK: Adding tasks to a dispatch group 
    dispatch_group_enter(loadServiceGroup) 

    // here i may start MULTPILE functions that are asynchronous. For example: 
    for i in stuff { 
     estore.fetchRemindersMatchingPredicate(remindersPredicate) { 
      // MARK: Begininning of thread 

      // does something here. E.g., count the elements: 
      counter += 1 

      // update the UI      
      dispatch_async(dispatch_get_main_queue()) { 
       self.sendChangedNotification()  // reloads the tableview. 
       // WARNING: I CAN'T JUST SHOW THE counter RESULTS HERE BECAUSE IT MIGHT NOT BE DONE YET. IT IS ASYNCHRONOUS, IT MIGHT STILL BE RUNNING. 
      } 
     } 

     // STEP 3 OF CREATING AN OVERALL COMPLETION BLOCK: Leave dispatch group. This must be done at the end of the completion block. 
     dispatch_group_leave(loadServiceGroup) 

     // MARK: End of thread 
    } 

    // STEP 4 OF CREATING AN OVERALL COMPLETION BLOCK: Acting when the group is finished 
    dispatch_group_notify(loadServiceGroup, dispatch_get_main_queue(), { 
     // do something when asychrounous call block (above) has finished running. E.g.: 
     print("number of elements: \(counter)") 

     // Assess any errors 
     var overallError: NSError? = nil; 

     if configError != nil || preferenceError != nil { 
      // Either make a new error or assign one of them to the overall error. 
      overallError = configError ?? preferenceError 
     } 

     // Call the completed function passed to foo. This will contain additional stuff that I want executed in the end. 
     completed(overallError) 
    }) 
} 

Answer 1

正に、あなたがしていることを完全に理解していません。しかし、私は常にすべての非同期関数が終了したかどうかを判断するためにカウンタ変数を使用します。

func foo(completionHandler: (success: Bool) -> Void) { 
    var numberOfTasks = 0 
    for data in datasource { 
     // do something preparing 
     numberOfTasks += 1 
    } 

    var numberOfDones = 0 
    objc_sync_enter(numberOfDones) 
    data.foo(completionHandler:(){ 
     // do something handling outcome 
     numberOfDones += 1 
     if numberOfDones == numberOfTasks { 
      completionHandler(true) 
     } 
    }) 
    objc_sync_exit(numberOfDones) 
} 

メカニズムは、我々は、タスクの総数が行われることを知っていることであり、各タスクのために、私たちは、完了イベントをキャッチすることができ、その結果、我々はnumberOfDonesを追加しました。したがって、numberOfDones == numberOfTasksの場合は、これが最後のものであることがわかります。すでに完了しています。

コードに基づいて、このアイデアを適用しようとしました。

func foo(stuff: AnArrayOfObjects, completed: ([NSError]?)->()) { 
    // STEP 1 OF CREATING AN OVERALL COMPLETION BLOCK: Create a dispatch group. 
    let loadServiceGroup: dispatch_group_t = dispatch_group_create() 

    // Define errors to be processed when everything is complete. 
    // One error per service; in this example we'll have two 
    let configError: NSError? = nil 
    let preferenceError: NSError? = nil 

    // some more preprocessing/variable declarations here. E.g.: 
    var counter = 0 

    // STEP 2 OF CREATING AN OVERALL COMPLETION BLOCK: Adding tasks to a dispatch group 
    dispatch_group_enter(loadServiceGroup) 

    // here i may start MULTPILE functions that are asynchronous. For example: 
    for i in stuff { 
     estore.fetchRemindersMatchingPredicate(remindersPredicate) { 
      // MARK: Begininning of thread 

      // does something here. E.g., count the elements: 
      counter += 1 

      // update the UI 
      dispatch_async(dispatch_get_main_queue()) { 
       self.sendChangedNotification()  // reloads the tableview. 
       // WARNING: I CAN'T JUST SHOW THE counter RESULTS HERE BECAUSE IT MIGHT NOT BE DONE YET. IT IS ASYNCHRONOUS, IT MIGHT STILL BE RUNNING. 
      } 
     } 

     // STEP 3 OF CREATING AN OVERALL COMPLETION BLOCK: Leave dispatch group. This must be done at the end of the completion block. 
     dispatch_group_leave(loadServiceGroup) 

     // MARK: End of thread 
    } 

    var numberOfDones = 0 
    var errors = [NSError]() 

    // STEP 4 OF CREATING AN OVERALL COMPLETION BLOCK: Acting when the group is finished 
    objc_sync_enter(numberOfDones) 
    dispatch_group_notify(loadServiceGroup, dispatch_get_main_queue(), { 
     // do something when asychrounous call block (above) has finished running. E.g.: 
     print("number of elements: \(counter)") 

     // Assess any errors 
     var overallError: NSError? = nil; 

     if configError != nil || preferenceError != nil { 
      // Either make a new error or assign one of them to the overall error. 
      errors.append(configError ?? preferenceError!) 
     } 

     numberOfDones += 1 
     if numberOfDones == counter { 
      // Call the completed function passed to foo. This will contain additional stuff that I want executed in the end. 
      completed(errors) 
     } 
    }) 
    objc_sync_exit(numberOfDones) 
} 

EDIT：@CouchDeveloperに

おかげで私の回答にコメントしました。私はカウンタ変数を同期させることによってスレッドを安全にする別の解決法を考え出します。答えは更新され、以下のソリューション

https://gist.github.com/qiuyujx/7173ea663308cc03f07e8a5c09cf4cba