Investigate #3007; defensive code in maintenance events, and resubscription; fix inappropriate async void (#3013)

Author: mgravell

src/StackExchange.Redis/Maintenance/AzureMaintenanceEvent.cs

@@ -124,24 +124,32 @@ internal static async Task AddListenerAsync(ConnectionMultiplexer multiplexer, A
             try
             {
                 var sub = multiplexer.GetSubscriber();
-                if (sub == null)
+                // ReSharper disable once ConditionIsAlwaysTrueOrFalseAccordingToNullableAPIContract
+                if (sub is null)
                 {
                     log?.Invoke("Failed to GetSubscriber for AzureRedisEvents");
                     return;
                 }
 
-                await sub.SubscribeAsync(RedisChannel.Literal(PubSubChannelName), async (_, message) =>
+                await sub.SubscribeAsync(RedisChannel.Literal(PubSubChannelName), (_, message) =>
                 {
-                    var newMessage = new AzureMaintenanceEvent(message!);
-                    newMessage.NotifyMultiplexer(multiplexer);
+                    try
+                    {
+                        var newMessage = new AzureMaintenanceEvent(message!);
+                        newMessage.NotifyMultiplexer(multiplexer);
 
-                    switch (newMessage.NotificationType)
+                        switch (newMessage.NotificationType)
+                        {
+                            case AzureNotificationType.NodeMaintenanceEnded:
+                            case AzureNotificationType.NodeMaintenanceFailoverComplete:
+                            case AzureNotificationType.NodeMaintenanceScaleComplete:
+                                multiplexer.ReconfigureAsync($"Azure Event: {newMessage.NotificationType.ToString()}").RedisFireAndForget();
+                                break;
+                        }
+                    }
+                    catch (Exception e)
                     {
-                        case AzureNotificationType.NodeMaintenanceEnded:
-                        case AzureNotificationType.NodeMaintenanceFailoverComplete:
-                        case AzureNotificationType.NodeMaintenanceScaleComplete:
-                            await multiplexer.ReconfigureAsync($"Azure Event: {newMessage.NotificationType}").ForAwait();
-                            break;
+                        log?.Invoke($"Encountered exception: {e}");
                     }
                 }).ForAwait();
             }

src/StackExchange.Redis/RedisSubscriber.cs

@@ -135,7 +135,14 @@ internal long EnsureSubscriptions(CommandFlags flags = CommandFlags.None)
             var subscriber = DefaultSubscriber;
             foreach (var pair in subscriptions)
             {
-                count += pair.Value.EnsureSubscribedToServer(subscriber, pair.Key, flags, true);
+                try
+                {
+                    count += pair.Value.EnsureSubscribedToServer(subscriber, pair.Key, flags, true);
+                }
+                catch (Exception ex)
+                {
+                    OnInternalError(ex);
+                }
             }
             return count;
         }