From e0e2c3627c97691fee57fe43b9b11e28be8679c1 Mon Sep 17 00:00:00 2001
From: Paul Pacheco <paul.pacheco@aa.com>
Date: Wed, 17 Mar 2021 16:56:05 -0500
Subject: [PATCH] perf: allocation free send to observers

---
 .../GlobalInterestManager.cs                  | 10 ++++
 .../InterestManagement/InterestManager.cs     | 32 ++++++++++++
 Assets/Mirage/Runtime/NetworkIdentity.cs      | 51 ++++++++++++++-----
 3 files changed, 79 insertions(+), 14 deletions(-)

diff --git a/Assets/Mirage/Runtime/InterestManagement/GlobalInterestManager.cs b/Assets/Mirage/Runtime/InterestManagement/GlobalInterestManager.cs
index 02e5fa0e44d..47d18db7071 100644
--- a/Assets/Mirage/Runtime/InterestManagement/GlobalInterestManager.cs
+++ b/Assets/Mirage/Runtime/InterestManagement/GlobalInterestManager.cs
@@ -7,6 +7,16 @@ namespace Mirage.InterestManagement
     /// </summary>
     public class GlobalInterestManager : InterestManager
     {
+        public override void ForEach<T>(NetworkIdentity identity, T action)
+        {
+            // avoids allocations by looping directly on the HashSet
+            // which avoids boxing the IEnumerator
+            foreach (INetworkPlayer player in ServerObjectManager.Server.Players)
+            {
+                action.Run(player);
+            }
+        }
+
         public override IReadOnlyCollection<INetworkPlayer> Observers(NetworkIdentity identity)
         {
             return ServerObjectManager.Server.Players;
diff --git a/Assets/Mirage/Runtime/InterestManagement/InterestManager.cs b/Assets/Mirage/Runtime/InterestManagement/InterestManager.cs
index 7c0c3ca8237..322ca43090e 100644
--- a/Assets/Mirage/Runtime/InterestManagement/InterestManager.cs
+++ b/Assets/Mirage/Runtime/InterestManagement/InterestManager.cs
@@ -13,6 +13,19 @@ namespace Mirage.InterestManagement
     /// </summary>
     public abstract class InterestManager : MonoBehaviour
     {
+
+        /// <summary>
+        /// Action to execute per observer.
+        /// This is equivalent to <see cref="Action{T}"/>
+        /// but it allows for creating an allocation free "delegate"
+        /// This is used in the hot path.
+        /// </summary>
+        public interface PlayerAction
+        {
+            void Run(INetworkPlayer player);
+        }
+
+
         public ServerObjectManager ServerObjectManager;
 
         public void Start()
@@ -29,6 +42,25 @@ public void Start()
             server.Authenticated.AddListener(OnAuthenticated);
         }
 
+        /// <summary>
+        /// Executes an action for every player that can observe an object
+        /// allocation free.
+        /// </summary>
+        /// <typeparam name="T">The action type</typeparam>
+        /// <param name="identity">The object that we are observing</param>
+        /// <param name="action">The action to execute for every observer</param>
+        public virtual void ForEach<T>(NetworkIdentity identity, T action) where T : struct, PlayerAction
+        {
+            // this is the default implementation which works,  but will allocate
+            // by boxing the IEnumerator.
+            // implementations of InterestManager should override this method
+            // and provide an allocation free alternative.
+            foreach (INetworkPlayer player in Observers(identity))
+            {
+                action.Run(player);
+            }
+        }
+
         /// <summary>
         /// Invoked when a player joins the server
         /// It should show all objects relevant to that player
diff --git a/Assets/Mirage/Runtime/NetworkIdentity.cs b/Assets/Mirage/Runtime/NetworkIdentity.cs
index 84d650a749d..e6f7cf7ab2d 100644
--- a/Assets/Mirage/Runtime/NetworkIdentity.cs
+++ b/Assets/Mirage/Runtime/NetworkIdentity.cs
@@ -1040,6 +1040,28 @@ void SendUpdateVarsMessage()
 
         static readonly List<INetworkPlayer> connectionsExcludeSelf = new List<INetworkPlayer>(100);
 
+
+        // this is basically a delegate for player.Send,
+        // but it is allocation free
+        readonly struct SendAction : InterestManager.PlayerAction
+        {
+            private readonly ArraySegment<byte> data;
+            private readonly int channel;
+            private readonly INetworkPlayer owner;
+
+            internal SendAction(ArraySegment<byte> data, int channel, INetworkPlayer owner)
+            {
+                this.data = data;
+                this.channel = channel;
+                this.owner = owner;
+            }
+            public void Run(INetworkPlayer player)
+            {
+                if (player != owner)
+                    player.Send(data, channel);
+            }
+        }
+
         /// <summary>
         /// this is like SendToReady - but it doesn't check the ready flag on the connection.
         /// this is used for ObjectDestroy messages.
@@ -1055,21 +1077,22 @@ internal void SendToObservers<T>(T msg, bool includeOwner = true, int channelId
             if (Observers.Count == 0)
                 return;
 
-            if (includeOwner)
-            {
-                NetworkServer.SendToMany(Observers, msg, channelId);
-            }
-            else
+            using (PooledNetworkWriter writer = NetworkWriterPool.GetWriter())
             {
-                connectionsExcludeSelf.Clear();
-                foreach (INetworkPlayer player in Observers)
-                {
-                    if (ConnectionToClient != player)
-                    {
-                        connectionsExcludeSelf.Add(player);
-                    }
-                }
-                NetworkServer.SendToMany(connectionsExcludeSelf, msg, channelId);
+                // pack message into byte[] once
+                MessagePacker.Pack(msg, writer);
+                var segment = writer.ToArraySegment();
+                int count = Observers.Count;
+
+                InterestManager interestManager = ServerObjectManager.InterestManager;
+
+                // just a delegate to call send, but allocation free
+                SendAction action = new SendAction(segment, channelId, includeOwner ? null : ConnectionToClient);
+
+
+                interestManager.ForEach(this, action);
+
+                NetworkDiagnostics.OnSend(msg, channelId, segment.Count, count);
             }
         }