如何在Swift 3中创建线程安全变量? [英] How create thread safe variable in Swift 3?

问题描述

我有单例课程

class DeviceController:NSObject, CocoaMQTTDelegate {
     static let sharedInstance = DeviceController()
     var deviceOnArray:[String] = []
     var deviceOffArray:[String] = []
     private override init() {

        clientID = "xyz-" + String(ProcessInfo().processIdentifier)
        mqtt = CocoaMQTT(clientID: clientID, host: "device_controller.xyz.net", port: 1883)
        mqtt.username = "username"
        mqtt.password = "password"
        mqtt.willMessage = CocoaMQTTWill(topic: "/will", message: "dieout")
        mqtt.keepAlive = 30
        mqtt.cleanSession = true
        DeviceController.isConnecting = true
        super.init()
        mqtt.delegate = self
        mqtt.connect()
        self.registerBackgroundTask()
    }
   func sendArm(topic:String){
      // add device to deviceOnArray
   }
   func sendDisarm(topic:String){
      // remove device from deviceOnArray if exist here if I check by code that device is in array it returns false but on console if print it contains the device, It only heppens when I call sendArm and sendDisarm with a second.
     let lockQueue = DispatchQueue(label: "com.test.LockQueue")
        lockQueue.sync() {
           // all code now inside this
         }
     // I also used above code but it's not working
   }


}

如果您阅读代码，那么您会知道我在从deviceOnArray/deviceOffArray读取正确的值时遇到问题，我不确定如何解释此问题，但是我认为这里需要的是Obj-C原子线程安全的多变的.知道如何创建一个吗?

If you read the code then you'll know that I am facing problem in reading correct value from deviceOnArray/deviceOffArray, I am not sure how to explain this problem but I think what I need here is Obj-C atomic thread safe variable. Any idea how create one ?

推荐答案

您可以使用串行分派队列来确保仅以线程安全的方式更新阵列.

You can use a serial dispatch queue to ensure that the array is only updated in a thread safe manner.

最好也将您的deviceOnArray属性更改为private，以确保其他对象无法访问它.如果需要将此数组公开给其他对象，请通过计算属性来实现.例如

It is also best to change your deviceOnArray property to private to ensure that it cannot be accessed by some other object. If you need to expose this array to other objects, do so via a computed property. e.g.

class DeviceController:NSObject, CocoaMQTTDelegate {
     static let sharedInstance = DeviceController()
     private var deviceOnArray:[String] = []
     var deviceOn: [String] {
         return self.deviceOnArray
     }

     var deviceOffArray:[String] = []
     private let dispatchQueue = DispatchQueue(label:"DeviceControllerQueue")

     private override init() {

        clientID = "xyz-" + String(ProcessInfo().processIdentifier)
        mqtt = CocoaMQTT(clientID: clientID, host: "device_controller.xyz.net", port: 1883)
        mqtt.username = "username"
        mqtt.password = "password"
        mqtt.willMessage = CocoaMQTTWill(topic: "/will", message: "dieout")
        mqtt.keepAlive = 30
        mqtt.cleanSession = true
        DeviceController.isConnecting = true
        super.init()
        mqtt.delegate = self
        mqtt.connect()
        self.registerBackgroundTask()
    }
   func sendArm(topic:String){
      // add device to deviceOnArray
       self.dispatchQueue.sync {
           deviceOnArray.append(topic)
       }
   }

   func sendDisarm(topic:String){
      // remove device from deviceOnArray if exist here.
       self.dispatchQueue.sync {
           if let index = self.deviceOnArray.index(of: topic) {
               self.deviceOnArray.remove(at: index)
           }
       }
   }
}

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