fixing the last unanswered write time; number was garbage

src/StackExchange.Redis/ConnectionMultiplexer.cs

@@ -742,9 +742,12 @@ private async Task<bool> WaitAllIgnoreErrorsAsync(Task[] tasks, int timeoutMilli
         internal void OnHashSlotMoved(int hashSlot, EndPoint old, EndPoint @new)
         {
             var handler = HashSlotMoved;
-            if (handler != null) ConnectionMultiplexer.CompleteAsWorker(
+            if (handler != null)
+            {
+                ConnectionMultiplexer.CompleteAsWorker(
                   new HashSlotMovedEventArgs(handler, this, hashSlot, old, @new));
             }
+        }
 
         /// <summary>
         /// Compute the hash-slot of a specified key

src/StackExchange.Redis/Message.cs

@@ -666,6 +666,7 @@ internal void SetWriteTime()
             }
         }
         private int _writeTickCount;
+        public int GetWriteTime() => Volatile.Read(ref _writeTickCount);
 
         private void SetNeedsTimeoutCheck() => Flags |= NeedsAsyncTimeoutCheckFlag;
         internal bool HasAsyncTimedOut(int now, int timeoutMilliseconds, out int millisecondsTaken)

src/StackExchange.Redis/PhysicalBridge.cs

@@ -286,7 +286,7 @@ private void ShutdownSubscriptionQueue()
             }
         }
 
-        internal bool TryEnqueueBackgroundSubscriptionWrite(PendingSubscriptionState state)
+        internal bool TryEnqueueBackgroundSubscriptionWrite(in PendingSubscriptionState state)
             => isDisposed ? false : (_subscriptionBackgroundQueue ?? GetSubscriptionQueue()).Writer.TryWrite(state);
 
         internal void GetOutstandingCount(out int inst, out int qs, out int @in, out int qu)
@@ -443,7 +443,6 @@ private void AbandonPendingBacklog(Exception ex)
             Message next;
             do
             {
-                
                 lock (_backlog)
                 {
                     next = _backlog.Count == 0 ? null : _backlog.Dequeue();
@@ -737,11 +736,10 @@ private void StartBacklogProcessor()
             sched.Schedule(s_ProcessBacklog, _weakRefThis);
         }
 
-        static readonly Action<object> s_ProcessBacklog = s =>
+        private static readonly Action<object> s_ProcessBacklog = s =>
         {
             var wr = (WeakReference)s;
-            var bridge = wr.Target as PhysicalBridge;
-            if (bridge != null) bridge.ProcessBacklog();
+            if (wr.Target is PhysicalBridge bridge) bridge.ProcessBacklog();
         };
 
         private void CheckBacklogForTimeouts() // check the head of the backlog queue, consuming anything that looks dead

src/StackExchange.Redis/PhysicalConnection.cs

@@ -52,7 +52,6 @@ private static readonly Message
         private int failureReported;
 
         private int lastWriteTickCount, lastReadTickCount, lastBeatTickCount;
-        private int firstUnansweredWriteTickCount;
 
         internal void GetBytes(out long sent, out long received)
         {
@@ -88,7 +87,6 @@ public PhysicalConnection(PhysicalBridge bridge)
 
         internal async Task BeginConnectAsync(TextWriter log)
         {
-            Thread.VolatileWrite(ref firstUnansweredWriteTickCount, 0);
             var bridge = BridgeCouldBeNull;
             var endpoint = bridge?.ServerEndPoint?.EndPoint;
             if (endpoint == null)
@@ -324,7 +322,17 @@ public Task FlushAsync()
                 {
                     int now = Environment.TickCount, lastRead = Thread.VolatileRead(ref lastReadTickCount), lastWrite = Thread.VolatileRead(ref lastWriteTickCount),
                         lastBeat = Thread.VolatileRead(ref lastBeatTickCount);
-                    int unansweredRead = Thread.VolatileRead(ref firstUnansweredWriteTickCount);
+
+                    int unansweredWriteTime = 0;
+                    lock (_writtenAwaitingResponse)
+                    {
+                        // find oldest message awaiting a response
+                        if (_writtenAwaitingResponse.Count != 0)
+                        {
+                            var next = _writtenAwaitingResponse.Peek();
+                            unansweredWriteTime = next.GetWriteTime();
+                        }
+                    }
 
                     var exMessage = new StringBuilder(failureType.ToString());
 
@@ -371,7 +379,7 @@ void add(string lk, string sk, string v)
                             add("Outstanding-Responses", "outstanding", GetSentAwaitingResponseCount().ToString());
                             add("Last-Read", "last-read", (unchecked(now - lastRead) / 1000) + "s ago");
                             add("Last-Write", "last-write", (unchecked(now - lastWrite) / 1000) + "s ago");
-                            add("Unanswered-Write", "unanswered-write", (unchecked(now - unansweredRead) / 1000) + "s ago");
+                            if(unansweredWriteTime != 0) add("Unanswered-Write", "unanswered-write", (unchecked(now - unansweredWriteTime) / 1000) + "s ago");
                             add("Keep-Alive", "keep-alive", bridge.ServerEndPoint?.WriteEverySeconds + "s");
                             add("Previous-Physical-State", "state", oldState.ToString());
                             add("Manager", "mgr", bridge.Multiplexer.SocketManager?.GetState());
@@ -696,9 +704,6 @@ internal void WriteHeader(RedisCommand command, int arguments, CommandBytes comm
             // ExecuteMessage should have dealt with everything else
             if (commandBytes.IsEmpty) throw ExceptionFactory.CommandDisabled(command);
 
-            // remember the time of the first write that still not followed by read
-            Interlocked.CompareExchange(ref firstUnansweredWriteTickCount, Environment.TickCount, 0);
-
             // *{argCount}\r\n      = 3 + MaxInt32TextLen
             // ${cmd-len}\r\n       = 3 + MaxInt32TextLen
             // {cmd}\r\n            = 2 + commandBytes.Length

src/StackExchange.Redis/RawResult.cs

@@ -291,7 +291,7 @@ internal bool GetBoolean()
             return AsGeoPosition(root.GetItems());
         }
 
-        static GeoPosition AsGeoPosition(Sequence<RawResult> coords)
+        private static GeoPosition AsGeoPosition(in Sequence<RawResult> coords)
         {
             double longitude, latitude;
             if (coords.IsSingleSegment)

src/StackExchange.Redis/RedisSubscriber.cs

@@ -17,7 +17,7 @@ internal static void CompleteAsWorker(ICompletable completable)
             if (completable != null) ThreadPool.QueueUserWorkItem(s_CompleteAsWorker, completable);
         }
 
-        static readonly WaitCallback s_CompleteAsWorker = s => ((ICompletable)s).TryComplete(true);
+        private static readonly WaitCallback s_CompleteAsWorker = s => ((ICompletable)s).TryComplete(true);
 
         internal static bool TryCompleteHandler<T>(EventHandler<T> handler, object sender, T args, bool isAsync) where T : EventArgs, ICompletable
         {
@@ -261,7 +261,6 @@ public static PendingSubscriptionState Create(RedisChannel channel, Subscription
 
                 private PendingSubscriptionState(object asyncState, RedisChannel channel, Subscription subscription, CommandFlags flags, bool subscribe, bool internalCall, bool isSlave)
                 {
-                    
                     var cmd = subscribe
                         ? (channel.IsPatternBased ? RedisCommand.PSUBSCRIBE : RedisCommand.SUBSCRIBE)
                         : (channel.IsPatternBased ? RedisCommand.PUNSUBSCRIBE : RedisCommand.UNSUBSCRIBE);

src/StackExchange.Redis/ResultProcessor.cs

@@ -1114,7 +1114,7 @@ public RedisChannelArrayProcessor(RedisChannel.PatternMode mode)
                 this.mode = mode;
             }
 
-            readonly struct ChannelState // I would use a value-tuple here, but that is binding hell
+            private readonly struct ChannelState // I would use a value-tuple here, but that is binding hell
             {
                 public readonly byte[] Prefix;
                 public readonly RedisChannel.PatternMode Mode;

src/StackExchange.Redis/ServerSelectionStrategy.cs

@@ -8,7 +8,9 @@ internal sealed class ServerSelectionStrategy
     {
         public const int NoSlot = -1, MultipleSlots = -2;
         private const int RedisClusterSlotCount = 16384;
+#pragma warning disable IDE1006 // Naming Styles
         private static ReadOnlySpan<ushort> s_crc16tab => new ushort[]
+#pragma warning restore IDE1006 // Naming Styles
             { // this syntax allows a special-case population implementation by the compiler/JIT
                 0x0000,0x1021,0x2042,0x3063,0x4084,0x50a5,0x60c6,0x70e7,
                 0x8108,0x9129,0xa14a,0xb16b,0xc18c,0xd1ad,0xe1ce,0xf1ef,
@@ -72,6 +74,7 @@ private static unsafe int GetClusterSlot(in RedisKey key)
             {
                 var blob = (byte[])key;
                 fixed (byte* ptr = blob)
+                {
                     fixed (ushort* crc16tab = s_crc16tab)
                     {
                         int offset = 0, count = blob.Length, start, end;
@@ -90,6 +93,7 @@ private static unsafe int GetClusterSlot(in RedisKey key)
                     }
                 }
             }
+        }
 
         public ServerEndPoint Select(Message message)
         {