问题描述
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，函数将完成并退出dispatchGroup。问题是计数器== 0多次为true（退出dispatchGroup时明显崩溃）。我真的不明白为什么会多次满足这个条件。代码是线性的，我看不出是什么原因造成的。任何帮助都非常感谢。这让我发疯。
解决方法
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，以说明这一点。如果运行几次，最终将达到发生问题的相同条件。
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,doubleCount)
return
}
}
}
}
输出：
Completed: true,Counter: 0,Double Count: 1
Completed: true,Double Count: 1
*******************************************************************
***** Counter: 0,Double Count: 1,Symbol Index: 15
*******************************************************************
Completed: true,Double Count: 2
Completed: true,Symbol Index: 26
*******************************************************************
Completed: true,Symbol Index: 57
*******************************************************************
Completed: true,Double Count: 2
*******************************************************************
***** Counter: 0,Symbol Index: 3
*******************************************************************
Completed: true,Double Count: 2
最后，我通过使用DispatchGroup来解决此问题，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：是否有可能遇到与以前相同的问题？例如，说我有2个项目的循环。第一个项目进入组，并说第二个项目进入循环之前，异步调用返回一个值，第一个项目退出组。此时，在第二个项目进入该组之前，应触发.notify，并且完成第二个项目之前，completion（true）存在该函数。这可能吗？