refs #15264 Implemented locking for notifications Queue in ApnsConnec…

…tion

suggested in Redth#672 (comment)

PushSharp.Apple/ApnsConnection.cs

@@ -115,18 +115,21 @@ async Task SendBatch ()
 
             // Pause the timer
             timerBatchWait.Change (Timeout.Infinite, Timeout.Infinite);
-
-            if (notifications.Count <= 0)
-                return;
-
+
             // Let's store the batch items to send internally
             var toSend = new List<CompletableApnsNotification> ();
 
-            while (notifications.Count > 0 && toSend.Count < Configuration.InternalBatchSize) {
-                var n = notifications.Dequeue ();
-                toSend.Add (n);
-            }
+            lock (notificationBatchQueueLock)
+            {
+                if (notifications.Count <= 0)
+                    return;
 
+                while (notifications.Count > 0 && toSend.Count < Configuration.InternalBatchSize)
+                {
+                    var n = notifications.Dequeue();
+                    toSend.Add(n);
+                }
+            }
 
             Log.Info ("APNS-Client[{0}]: Sending Batch ID={1}, Count={2}", id, batchId, toSend.Count);
 
@@ -305,8 +308,11 @@ async Task Reader ()
             // The remaining items in the list were sent after the failed notification
             // we can assume these were ignored by apple so we need to send them again
             // Requeue the remaining notifications
-            foreach (var s in sent)
-                notifications.Enqueue (s.Notification);
+            lock (notificationBatchQueueLock)
+            {
+                foreach (var s in sent)
+                    notifications.Enqueue(s.Notification);
+            }
 
             // Clear our sent list
             sent.Clear ();