[FSSDK-12153] chore: update event retry strategy

Sources/Customization/DefaultEventDispatcher.swift

@@ -53,6 +53,11 @@ open class DefaultEventDispatcher: BackgroundingCallbacks, OPTEventDispatcher {
     // network reachability
     let reachability = NetworkReachability(maxContiguousFails: 1)
 
+    // sync group used to ensure that the flushEvents is synchronous for close()
+    let notify = DispatchGroup()
+    // track if flush is currently in progress
+    private var isFlushing = false
+
     public init(batchSize: Int = DefaultValues.batchSize,
                 backingStore: DataStoreType = .file,
                 dataStoreName: String = "OPTEventQueue",
@@ -107,69 +112,111 @@ open class DefaultEventDispatcher: BackgroundingCallbacks, OPTEventDispatcher {
         completionHandler?(.success(event.body))
     }
 
-    // notify group used to ensure that the sendEvent is synchronous.
-    // used in flushEvents
-    let notify = DispatchGroup()
-
+    // Per-batch retry: Each batch gets up to 3 attempts with exponential backoff
+    // Global failure counter stops processing after 3 consecutive batch failures
+
     open func flushEvents() {
         queueLock.async {
-            // we don't remove anthing off of the queue unless it is successfully sent.
-            var failureCount = 0
+            guard !self.isFlushing else { return }
 
-            func removeStoredEvents(num: Int) {
-                if let removedItem = self.eventQueue.removeFirstItems(count: num), removedItem.count > 0 {
-                    // avoid event-log-message preparation overheads with closure-logging
-                    self.logger.d({ "Removed stored \(num) events starting with \(removedItem.first!)" })
-                } else {
-                    self.logger.e("Failed to removed \(num) events")
-                }
-            }
+            self.isFlushing = true
+            self.notify.enter()
 
-            while let eventsToSend: [EventForDispatch] = self.eventQueue.getFirstItems(count: self.batchSize) {
-                let (numEvents, batched) = eventsToSend.batch()
-
-                guard numEvents > 0 else { break }
-
-                guard let batchEvent = batched else {
-                    // discard an invalid event that causes batching failure
-                    // - if an invalid event is found while batching, it batches all the valid ones before the invalid one and sends it out.
-                    // - when trying to batch next, it finds the invalid one at the header. It discards that specific invalid one and continue batching next ones.
-
-                    removeStoredEvents(num: 1)
-                    continue
-                }
-
-                // we've exhuasted our failure count.  Give up and try the next time a event
-                // is queued or someone calls flush (changed to >= so that retried exactly "maxFailureCount" times).
-                if failureCount >= DefaultValues.maxFailureCount {
-                    self.logger.e(.eventSendRetyFailed(failureCount))
-                    break
-                }
-
-                // make the send event synchronous. enter our notify
-                self.notify.enter()
-                self.sendEvent(event: batchEvent) { (result) -> Void in
-                    switch result {
-                    case .failure(let error):
-                        self.logger.e(error.reason)
-                        failureCount += 1
-                    case .success:
-                        // we succeeded. remove the batch size sent.
-                        removeStoredEvents(num: numEvents)
-
-                        // reset failureCount
-                        failureCount = 0
+            self.processNextBatch(failureCount: 0)
+        }
+    }
+
+    private func processNextBatch(failureCount: Int) {
+        // Global failure counter across all batches in this flush
+        if failureCount >= DefaultValues.maxFailureCount {
+            self.logger.e(.eventSendRetyFailed(failureCount))
+            self.finishFlush()
+            return
+        }
+
+        // Check reachability
+        if self.reachability.shouldBlockNetworkAccess() {
+            self.logger.e("NetworkReachability down")
+            self.finishFlush()
+            return
+        }
+
+        guard let eventsToSend: [EventForDispatch] = self.eventQueue.getFirstItems(count: self.batchSize) else {
+            self.finishFlush()
+            return
+        }
+
+        let (numEvents, batchedEvent) = eventsToSend.batch()
+
+        guard numEvents > 0 else {
+            self.finishFlush()
+            return
+        }
+
+        guard let batchEvent = batchedEvent else {
+            // discard an invalid event that causes batching failure
+            // - if an invalid event is found while batching, it batches all the valid ones before the invalid one and sends it out.
+            // - when trying to batch next, it finds the invalid one at the header. It discards and continue with next batch
+            self.removeStoredEvents(num: 1)
+            self.processNextBatch(failureCount: failureCount)
+            return
+        }
+
+        self.sendBatch(event: batchEvent, numEvents: numEvents) { success in
+            if success {
+                self.removeStoredEvents(num: numEvents)
+                self.processNextBatch(failureCount: 0)
+            } else {
+                // Retry with backoff
+                let attempt = failureCount + 1
+                if attempt < DefaultValues.maxFailureCount {
+                    let delay = self.calculateRetryDelay(attempt: attempt)
+                    self.queueLock.asyncAfter(deadline: .now() + delay) {
+                        self.processNextBatch(failureCount: attempt)
                     }
-                    // our send is done.
-                    self.notify.leave()
-
+                } else {
+                    self.logger.e(.eventSendRetyFailed(attempt))
+                    self.finishFlush()
                 }
-                // wait for send
-                self.notify.wait()
             }
         }
     }
 
+    private func sendBatch(event: EventForDispatch, numEvents: Int, completion: @escaping (Bool) -> Void) {
+        self.sendEvent(event: event) { result in
+            switch result {
+            case .success:
+                completion(true)
+            case .failure(let error):
+                self.logger.e(error.reason)
+                completion(false)
+            }
+        }
+    }
+
+    private func finishFlush() {
+        self.isFlushing = false
+        self.notify.leave()
+    }
+
+    private func removeStoredEvents(num: Int) {
+        if let removedItem = self.eventQueue.removeFirstItems(count: num), removedItem.count > 0 {
+            self.logger.d({ "Removed \(num) event(s) from queue starting with \(removedItem.first!)" })
+        } else {
+            self.logger.e("Failed to remove \(num) event(s) from queue")
+        }
+    }
+
+    /// Calculate retry delay using exponential backoff
+    /// - Parameter attempt: Current attempt number (1, 2, 3)
+    /// - Returns: Delay in seconds (200ms, 400ms, 800ms, capped at 1s)
+    private func calculateRetryDelay(attempt: Int) -> TimeInterval {
+        let retryStrategy = RetryStrategy(maxRetries: 2,
+                                          initialInterval: 0.2,
+                                          maxInterval: 1.0)
+        return retryStrategy.delayForRetry(attempt: attempt)
+    }
+
     open func sendEvent(event: EventForDispatch, completionHandler: @escaping DispatchCompletionHandler) {
 
         if self.reachability.shouldBlockNetworkAccess() {
@@ -211,7 +258,14 @@ open class DefaultEventDispatcher: BackgroundingCallbacks, OPTEventDispatcher {
 
     open func close() {
         self.flushEvents()
+        // Ensure flush async block has started
         self.queueLock.sync {}
+        // Wait for the flush to complete with a safety timeout.
+        // We use a 10-second timeout to prevent the app from hanging indefinitely during shutdown.
+        // If the flush takes longer (e.g. due to slow network or large queue), we proceed to close
+        // to avoid the OS watchdog killing the app for blocking the main thread for too long.
+        // This ensures a "best effort" flush while prioritizing a safe and graceful exit.
+        _ = self.notify.wait(timeout: .now() + 10.0)
     }
 
 }

Sources/Extensions/ArrayEventForDispatch+Extension.swift

@@ -98,7 +98,7 @@ extension Array where Element == EventForDispatch {
             // no batched event since the first event is invalid. notify so that it can be removed.
             return (1, nil)
         }
-
+        
         return (eventsBatched.count, makeBatchEvent(base: eventsBatched.first!, visitors: visitors, url: url))
     }
 
@@ -112,7 +112,7 @@ extension Array where Element == EventForDispatch {
                                     anonymizeIP: base.anonymizeIP,
                                     enrichDecisions: true,
                                     region: base.region)
-        
+
         guard let data = try? JSONEncoder().encode(batchEvent) else {
             return nil
         }

Sources/ODP/OdpConfig.swift

@@ -48,7 +48,7 @@ class OdpConfig {
             // disable future event queueing if datafile has no ODP integrations.
             self.odpServiceIntegrated = .notIntegrated
         }
-
+        
         if self.apiKey == apiKey, self.apiHost == apiHost, self.segmentsToCheck == segmentsToCheck {
             return false
         } else {