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我有一个转义函数，一旦满足条件就完成：

  private func xxxfastLoadLSecurityDescriptions(session: URLSession, mySymbols: [String]?, completion: @escaping(Bool) ->())    {
        
        var counter = mySymbols?.count ?? 0
        if counter == 0 { completion(false) }
        var doubleCount = 0
        // print("DESCRIPTION Starting Counter = \(counter)")
        
        for symbolIndex in 0..<(mySymbols?.count ?? 0) {
            guard let mySymbol = mySymbols?[symbolIndex] else { print("ERROR in fastLoadLSecurityDescriptions loop: No Symbol") ;  continue }
            guard let myGetDescriptionRequest = GenericDataRequest(dataToSend: [mySymbol], token: sessionToken, mgbRoute: MGBServerRoutes.retrieveSecurityDescriptionsRoute!)
            else { print("Error Getting Security Description Request for \(mySymbol)") ; return }
            
            mySessionSendMGBGenericRequest(session: session, request: myGetDescriptionRequest) { [weak self]  success, serverMessage, returnUNISecurityDescription in
                guard let self = self else { print("ERROR: self is nil") ; return }
                if returnUNISecurityDescription?.count == 0 { print("nil returnUniSecurityDescription for \(mySymbol)") }
                // print("DESCRIPTIONS COUNTER = \(counter)")
                counter -= 1
                var myDescription = UNISecurityDescription()
                if returnUNISecurityDescription != nil, returnUNISecurityDescription?.count != 0 { myDescription = returnUNISecurityDescription![0]  }
                if myDescription.name == nil || myDescription.name == "" { print("Error: No Name for \(String(describing: mySymbol))") }
                let myContainersIndices = self.myUNIList.singleContainer.indices.filter({ self.myUNIList.singleContainer[$0].ticker?.symbol == mySymbol })
                var myPathArray = [IndexPath]()
                for index in 0..<myContainersIndices.count {
                    self.myUNIList.singleContainer[myContainersIndices[index]].name = myDescription.name
                    self.myUNIList.singleContainer[myContainersIndices[index]].currencySymbol = myDescription.currencySymbol
                    self.myUNIList.singleContainer[myContainersIndices[index]].fillFundamentals() // --> Fills the outputs for sortdata
                    myPathArray.append(IndexPath(row: myContainersIndices[index], section: 0))
                }
                DispatchQueue.main.async {
                    self.filteredData = self.myUNIList.singleContainer
                    self.myCollection?.reloadItems(at: myPathArray)
                }
                if counter == 0     {   // THIS IS TRUE MORE THAN ONCE WHILE IT SHOULD NOT BE TRU MORE THAN ONCE
                    if doubleCount > 0 {    print("WHY!!!!")  }
                    doubleCount += 1
                    print("DESCRIPTIONS counter = \(counter) -> \(self.myUNIList.listName) - symbols: \(String(describing: mySymbols?.count)) \n==================================================\n")
                    DispatchQueue.main.async {   self.sortNormalTap("Load")  { _ in     self.displayAfterLoading()  } }
                    completion(true)
                    return
                }
            }
        }
    }

要满足的条件是 counter == 0。一旦满足，函数完成并退出 DispatchGroup。问题是 counter == 0 多次为真（退出 DispatchGroup 时明显崩溃）。我真的不明白为什么不止一次满足这个条件。代码非常线性，我看不出是什么原因造成的。非常感谢任何帮助。这让我快疯了。

4

2 回答 2

1

您的代码不是线程安全的，尤其是计数器。我使用相同的逻辑编写了一个示例来说明这一点。如果您运行它几次，您最终会遇到问题发生的相同情况。

override func viewDidLoad() {
    super.viewDidLoad()

    let mySymbols: [Int] = Array(0...100)

    for _ in 0..<100 {
        xxxfastLoadLSecurityDescriptions(session: URLSession.shared, mySymbols: mySymbols) { (success, counter, doubleCount) in
            print("Completed: \(success), Counter: \(counter), Double Count: \(doubleCount)")
        }
    }
}

private func xxxfastLoadLSecurityDescriptions(session: URLSession, mySymbols: [Int]?, completion: @escaping(Bool, Int, Int) ->())    {

    var counter = mySymbols?.count ?? 0

    if counter == 0 {
        return completion(false, -1, -1)
    }
    var doubleCount = 0

    for symbolIndex in 0..<(mySymbols?.count ?? 0) {
        guard let _ = mySymbols?[symbolIndex] else {
            print("Error")
            continue
        }

        DispatchQueue.global().asyncAfter(deadline: .now() + .milliseconds(Int.random(in: 50..<900))) {

            counter -= 1

            DispatchQueue.main.async {
                self.view.layoutIfNeeded()
            }

            if counter == 0 {
                if doubleCount > 0 {
                    // This will eventually print even though logically it shouldn't
                    print("*****Counter: \(counter), Double Count: \(doubleCount), Symbol Index: \(symbolIndex)")
                }
                doubleCount += 1
                completion(true, counter, doubleCount)
                return
            }
        }
    }
}

输出：

Completed: true, Counter: 0, Double Count: 1
Completed: true, Counter: 0, Double Count: 1
Completed: true, Counter: 0, Double Count: 1
Completed: true, Counter: 0, Double Count: 1
Completed: true, Counter: 0, Double Count: 1
Completed: true, Counter: 0, Double Count: 1
Completed: true, Counter: 0, Double Count: 1
Completed: true, Counter: 0, Double Count: 1
*******************************************************************
*****   Counter: 0, Double Count: 1, Symbol Index: 15   
*******************************************************************
Completed: true, Counter: 0, Double Count: 2
Completed: true, Counter: 0, Double Count: 1
Completed: true, Counter: 0, Double Count: 1
Completed: true, Counter: 0, Double Count: 1
*******************************************************************
*****   Counter: 0, Double Count: 1, Symbol Index: 26   
*******************************************************************
Completed: true, Counter: 0, Double Count: 2
Completed: true, Counter: 0, Double Count: 1
Completed: true, Counter: 0, Double Count: 1
Completed: true, Counter: 0, Double Count: 1
Completed: true, Counter: 0, Double Count: 1
*******************************************************************
*****   Counter: 0, Double Count: 1, Symbol Index: 57   
*******************************************************************
Completed: true, Counter: 0, Double Count: 2
*******************************************************************
*****   Counter: 0, Double Count: 1, Symbol Index: 3    
*******************************************************************
Completed: true, Counter: 0, Double Count: 2
于 2020-11-11T22:05:54.483 回答
1

最后，我使用 DispatchGroup 解决了这个问题，如下所示（简化代码）：

private func xxxFastLoadLSecurityDescriptions(session: URLSession, mySymbols: [String]?, completion: @escaping(Bool) ->())    {
    
    let myGroup = DispatchGroup()
    
    for symbolIndex in 0..<(mySymbols?.count ?? 0) {
        
        myGroup.enter()
    
        mySessionSendMGBGenericRequest(...) { [weak self] returnValue in
            
            guard let self = self else { myGroup.leave() ; return }
         // do some stuff with returnValue
            
            myGroup.leave()
        }
    }
    
    myGroup.notify(queue: .main, execute: {
        
        completion(true)
    })
}

我的问题是：我是否可能遇到与以前相同的问题？例如，假设我有 2 个项目的循环。第一项进入组并说在第二项进入循环之前异步调用返回一个值并且第一项退出组。此时，在第二项进入组之前，应该触发.notify，并且completion(true)在处理第二项之前存在该函数。这可能吗？

于 2020-11-12T08:57:42.657 回答