Only flush the output on a completely no-op call to WriteQueue; if work is...

Only flush the output on a completely no-op call to WriteQueue; if work is done, but it back in in the work-queue and retry; this adds a tiny tiny delay, but is enough to help reduce packet fragmentation from high-perf producers

StackExchange.Redis/StackExchange/Redis/PhysicalBridge.cs

@@ -10,7 +10,8 @@ namespace StackExchange.Redis
 {
     enum WriteResult
     {
-        QueueEmpty,
+        QueueEmptyAfterWrite,
+        NothingToDo,
         MoreWork,
         CompetingWriter,
         NoConnection,
@@ -529,17 +530,20 @@ internal WriteResult WriteQueue(int maxWork)
                     return WriteResult.NoConnection;
                 }
 
-                int count = 0;
                 Message last = null;
+                int count = 0;
                 while (true)
                 {
                     var next = queue.Dequeue();
                     if (next == null)
                     {
                         Trace("Nothing to write; exiting");
-                        Trace(last != null, "Flushed up to: " + last);
-                        conn.Flush();
-                        return WriteResult.QueueEmpty;
+                        if(count == 0)
+                        {
+                            conn.Flush(); // only flush on an empty run
+                            return WriteResult.NothingToDo;
+                        }
+                        return WriteResult.QueueEmptyAfterWrite;
                     }
                     last = next;
 
@@ -562,7 +566,11 @@ internal WriteResult WriteQueue(int maxWork)
             }
             catch (IOException ex)
             {
-                if (conn != null) conn.RecordConnectionFailed(ConnectionFailureType.SocketFailure, ex);
+                if (conn != null)
+                {
+                    conn.RecordConnectionFailed(ConnectionFailureType.SocketFailure, ex);
+                    conn = null;
+                }
                 AbortUnsent();
             }
             catch (Exception ex)
@@ -578,7 +586,7 @@ internal WriteResult WriteQueue(int maxWork)
                     Trace("Exiting writer");
                 }
             }
-            return queue.Any() ? WriteResult.MoreWork : WriteResult.QueueEmpty;
+            return queue.Any() ? WriteResult.MoreWork : WriteResult.QueueEmptyAfterWrite;
         }
 
         private void AbortUnsent()

StackExchange.Redis/StackExchange/Redis/PhysicalConnection.cs

@@ -12,14 +12,6 @@
 
 namespace StackExchange.Redis
 {
-    internal enum WorkState
-    {
-        Pending,
-        Failed,
-        NothingToDo,
-        Disconnected,
-        HasWork
-    }
 
     internal sealed partial class PhysicalConnection : IDisposable, ISocketCallback
     {

StackExchange.Redis/StackExchange/Redis/SocketManager.NoPoll.cs

@@ -6,7 +6,7 @@ partial class SocketManager
     {
         internal const SocketMode DefaultSocketMode = SocketMode.Async;
 
-        partial void OnAddRead(System.Net.Sockets.Socket socket, ISocketCallback callback)
+        private void OnAddRead(System.Net.Sockets.Socket socket, ISocketCallback callback)
         {
             throw new System.NotSupportedException();
         }

StackExchange.Redis/StackExchange/Redis/SocketManager.Poll.cs

@@ -71,7 +71,7 @@ private static void ProcessItems(Dictionary<IntPtr, SocketPair> socketLookup, Qu
             }
         }
 
-        partial void OnAddRead(Socket socket, ISocketCallback callback)
+        private void OnAddRead(Socket socket, ISocketCallback callback)
         {
             if (socket == null) throw new ArgumentNullException("socket");
             if (callback == null) throw new ArgumentNullException("callback");

StackExchange.Redis/StackExchange/Redis/SocketManager.cs

@@ -191,10 +191,6 @@ private void EndConnect(IAsyncResult ar)
             }
         }
 
-        /// <summary>
-        /// Adds a new socket and callback to the manager
-        /// </summary>
-        partial void OnAddRead(Socket socket, ISocketCallback callback);
         partial void OnDispose();
         partial void OnShutdown(Socket socket);
 
@@ -229,6 +225,7 @@ private void WriteAllQueues()
                 switch (bridge.WriteQueue(200))
                 {
                     case WriteResult.MoreWork:
+                    case WriteResult.QueueEmptyAfterWrite:
                         // back of the line!
                         lock (writeQueue)
                         {
@@ -240,7 +237,7 @@ private void WriteAllQueues()
                     case WriteResult.NoConnection:
                         Interlocked.Exchange(ref bridge.inWriteQueue, 0);
                         break;
-                    case WriteResult.QueueEmpty:
+                    case WriteResult.NothingToDo:
                         if (!bridge.ConfirmRemoveFromWriteQueue())
                         { // more snuck in; back of the line!
                             lock (writeQueue)
@@ -267,9 +264,10 @@ private void WriteOneQueue()
                 switch (bridge.WriteQueue(-1))
                 {
                     case WriteResult.MoreWork:
+                    case WriteResult.QueueEmptyAfterWrite:
                         keepGoing = true;
                         break;
-                    case WriteResult.QueueEmpty:
+                    case WriteResult.NothingToDo:
                         keepGoing = !bridge.ConfirmRemoveFromWriteQueue();
                         break;
                     case WriteResult.CompetingWriter: