使用 dispatchgroup 在 for 循環中等待任務完成，如果失敗則退出循環

Question

我試圖根據條件從 for 循環中退出，但我遇到了這個問題，因為它甚至沒有從循環中退出。 這是我的代碼的循環。

var isFailure = true
let dispatchGroup = DispatchGroup()
var myFailureTask: Int?
for item in 1...5 {
  dispatchGroup.enter()
  test(item: item, completion: {
    print("Success\(item)")
    dispatchGroup.leave()
  }, failureBlock: {
    print("Failure\(item)")
    myFailureTask = item
    dispatchGroup.leave()
    return
  })
  dispatchGroup.wait()
}
dispatchGroup.notify(queue: .main) {
  if let myFailure = myFailureTask {
    print("task failure \(myFailure)")
  } else {
    print("all task done")
  }
}
func test(item: Int,completion: @escaping(() -> ()), failureBlock: @escaping(() -> ())) {
    Thread.sleep(forTimeInterval: TimeInterval(item))
  isFailure = !isFailure
  if isFailure {
    failureBlock()
  } else {
    completion()
  }
}

Answer 1

return從當前 scope 返回。

在這種情況下，它從failureBlock: {}返回，而不是從 for 循環 scope 返回。

您必須重構代碼以實現您想要做的事情。

要么（如果此代碼同步執行）您可以返回success值true | 通過使function的返回類型為Bool並刪除failureBlock參數，從 function 中返回false 。

或者（如果此代碼異步執行）您必須考慮在觸發另一個任務之前等待一個任務完成/失敗。

更新

我認為以下可能是此代碼的簡化版本-

var isFailure: Bool = false

func callTest(for item: Int) {
    print("task initiated \(item)")
    test(item: item, completion: {
        print("task succeeded \(item)")
        if item < 5 {
            callTest(for: item+1)
        } else {
            print("all tasks done")
        }
    }, failureBlock: {
        print("task failed \(item)")
    })
}

func test(item: Int, completion: @escaping (() -> Void), failureBlock: @escaping (() -> Void)) {
    Thread.sleep(forTimeInterval: TimeInterval(item))
    isFailure.toggle()
    if isFailure {
        failureBlock()
    } else {
        completion()
    }
}

callTest(for: 1)

Answer 2

var isFailure = false
let dispatchGroup = DispatchGroup()
var myFailureTask: Int?
for item in 1...5 {
  dispatchGroup.enter()
  test(item: item, completion: {
    print("Success\(item)")
    dispatchGroup.leave()
  }, failureBlock: {
    print("Failure\(item)")
    myFailureTask = item
    dispatchGroup.leave()
  })
  if isFailure == true {
    break
  }
  dispatchGroup.wait()
}
dispatchGroup.notify(queue: .main) {
  if let myFailure = myFailureTask {
    print("task failure \(myFailure)")
  } else {
    print("all task done")
  }
}
func test(item: Int,completion: @escaping(() -> ()), failureBlock: @escaping(() -> ())) {
    Thread.sleep(forTimeInterval: TimeInterval(item))
  isFailure = !isFailure
  if isFailure {
    failureBlock()
  } else {
    completion()
  }
}```
Made few changes work like a charm.
Any one has better idea please comment