(chore): refactor atomic property to allow for atomic operations (#121)

* refactor atomic property to allow for atomic operations

* add one more performAtomic

Author: thomaszurkan-optimizely

OptimizelySDK/Customization/DefaultEventDispatcher.swift

@@ -67,7 +67,7 @@ open class DefaultEventDispatcher : BackgroundingCallbacks, OPTEventDispatcher {
     }
 
     deinit {
-        if let timer = timer.property {
+        timer.performAtomic() { (timer) in
             timer.invalidate()
         }
         unsubscribe()
@@ -206,7 +206,7 @@ open class DefaultEventDispatcher : BackgroundingCallbacks, OPTEventDispatcher {
     }
 
     func applicationDidEnterBackground() {
-        if let timer = timer.property {
+        timer.performAtomic() { (timer) in
             timer.invalidate()
         }
         timer.property = nil
@@ -231,7 +231,9 @@ open class DefaultEventDispatcher : BackgroundingCallbacks, OPTEventDispatcher {
             DispatchQueue.main.async {
                 self.timer.property = Timer.scheduledTimer(withTimeInterval: self.timerInterval, repeats: true) { (timer) in
                     if self.dataStore.count == 0 {
-                        self.timer.property?.invalidate()
+                        self.timer.performAtomic() { (timer) in
+                            timer.invalidate()
+                        }
                         self.timer.property = nil
                     }
                     else {

OptimizelySDK/OptimizelyTests/OptimizelyTests-APIs/OptimizelyManagerTests_Threading.swift

@@ -260,7 +260,6 @@ class OptimizelyManagerTests_Threading: XCTestCase {
         //let expectationBackground = XCTestExpectation(description: "waiting for background thread")
         let backgroundQueue = DispatchQueue(label: "mybackground", qos: DispatchQoS.default, attributes: DispatchQueue.Attributes.concurrent)
         let atomicBackground = AtomicProperty<[(enabled:Bool?, variation:String?)]>(property: [(enabled:Bool?, variation:String?)]())
-        let appendLock = DispatchQueue(label: "appendLock")
 
         let dispatchGroup = DispatchGroup()
 
@@ -270,8 +269,8 @@ class OptimizelyManagerTests_Threading: XCTestCase {
                 let enabled = try? optimizely2.isFeatureEnabled(featureKey: "feat", userId: self.userId, attributes: ["house": "Gryffindor"])
                 let variation = try? optimizely3.activate(experimentKey: "ab_running_exp_untargeted", userId: self.userId)
 
-                appendLock.sync {
-                    atomicBackground.property!.append((enabled: enabled!, variation: variation!))
+                atomicBackground.performAtomic() { (array) in
+                    array.append((enabled: enabled!, variation: variation!))
                 }
 
                 defer {

OptimizelySDK/Utils/AtomicProperty.swift

@@ -38,5 +38,16 @@ class AtomicProperty<T> {
     init() {
 
     }
+    
+    // perform an atomic operation on the atomic property
+    // the operation will not run if the property is nil.
+    public func performAtomic(atomicOperation:((_ prop:inout T)->Void)) {
+        lock.sync {
+            if var prop = _property {
+                atomicOperation(&prop)
+                _property = prop
+            }
+        }
+    }
 
 }