update

Doing a full pass on the internal usage of NetworkManager.ConnectedClientsIds and replacing with NetworkConnectionManager.ConnectedClientIds to remove any other potential small memory allocations.
The best savings will be where it is used in universal RPCs.

Author: NoelStephensUnity

com.unity.netcode.gameobjects/Runtime/Components/NetworkAnimator.cs

@@ -996,7 +996,7 @@ internal void CheckForAnimatorChanges()
                 {
                     // Just notify all remote clients and not the local server
                     m_ClientSendList.Clear();
-                    foreach (var clientId in NetworkManager.ConnectedClientsIds)
+                    foreach (var clientId in NetworkManager.ConnectionManager.ConnectedClientIds)
                     {
                         if (clientId == NetworkManager.LocalClientId || !NetworkObject.Observers.Contains(clientId))
                         {
@@ -1315,7 +1315,7 @@ private unsafe void SendParametersUpdateServerRpc(ParametersUpdateMessage parame
                 if (NetworkManager.ConnectedClientsIds.Count > (IsHost ? 2 : 1))
                 {
                     m_ClientSendList.Clear();
-                    foreach (var clientId in NetworkManager.ConnectedClientsIds)
+                    foreach (var clientId in NetworkManager.ConnectionManager.ConnectedClientIds)
                     {
                         if (clientId == serverRpcParams.Receive.SenderClientId || clientId == NetworkManager.ServerClientId || !NetworkObject.Observers.Contains(clientId))
                         {
@@ -1378,7 +1378,7 @@ private void SendAnimStateServerRpc(AnimationMessage animationMessage, ServerRpc
                 if (NetworkManager.ConnectedClientsIds.Count > (IsHost ? 2 : 1))
                 {
                     m_ClientSendList.Clear();
-                    foreach (var clientId in NetworkManager.ConnectedClientsIds)
+                    foreach (var clientId in NetworkManager.ConnectionManager.ConnectedClientIds)
                     {
                         if (clientId == serverRpcParams.Receive.SenderClientId || clientId == NetworkManager.ServerClientId || !NetworkObject.Observers.Contains(clientId))
                         {
@@ -1452,7 +1452,7 @@ internal void SendAnimTriggerServerRpc(AnimationTriggerMessage animationTriggerM
             InternalSetTrigger(animationTriggerMessage.Hash, animationTriggerMessage.IsTriggerSet);
 
             m_ClientSendList.Clear();
-            foreach (var clientId in NetworkManager.ConnectedClientsIds)
+            foreach (var clientId in NetworkManager.ConnectionManager.ConnectedClientIds)
             {
                 if (clientId == NetworkManager.ServerClientId || !NetworkObject.Observers.Contains(clientId))
                 {

com.unity.netcode.gameobjects/Runtime/Connection/NetworkConnectionManager.cs

@@ -148,12 +148,12 @@ internal void InvokeOnClientConnectedCallback(ulong clientId)
             }
 
             // Invoking connection event on non-authority local client. Need to calculate PeerIds.
-            var peerClientIds = new NativeArray<ulong>(Math.Max(NetworkManager.ConnectedClientsIds.Count - 1, 0), Allocator.Temp);
+            var peerClientIds = new NativeArray<ulong>(Math.Max(ConnectedClientIds.Count - 1, 0), Allocator.Temp);
             // `using var peerClientIds` or `using(peerClientIds)` renders it immutable...
             using var sentinel = peerClientIds;
 
             var idx = 0;
-            foreach (var peerId in NetworkManager.ConnectedClientsIds)
+            foreach (var peerId in ConnectedClientIds)
             {
                 if (peerId == NetworkManager.LocalClientId)
                 {

com.unity.netcode.gameobjects/Runtime/Core/NetworkBehaviourUpdater.cs

@@ -34,8 +34,11 @@ internal void NetworkBehaviourUpdate(bool forceSend = false)
 #endif
             try
             {
-                m_DirtyNetworkObjects.UnionWith(m_PendingDirtyNetworkObjects);
-                m_PendingDirtyNetworkObjects.Clear();
+                if (m_PendingDirtyNetworkObjects.Count > 0)
+                {
+                    m_DirtyNetworkObjects.UnionWith(m_PendingDirtyNetworkObjects);
+                    m_PendingDirtyNetworkObjects.Clear();
+                }
 
                 // NetworkObject references can become null, when hidden or despawned. Once NUll, there is no point
                 // trying to process them, even if they were previously marked as dirty.

com.unity.netcode.gameobjects/Runtime/Core/NetworkObject.cs

@@ -1616,7 +1616,7 @@ public void NetworkHide(ulong clientId)
                         // Send destroy call
                         size = NetworkManager.ConnectionManager.SendMessage(ref message, NetworkDelivery.ReliableSequenced, clientId);
                         // Broadcast the destroy to all clients so they can update their observers list
-                        foreach (var client in NetworkManager.ConnectedClientsIds)
+                        foreach (var client in NetworkManager.ConnectionManager.ConnectedClientIds)
                         {
                             if (client == clientId || client == NetworkManager.LocalClientId)
                             {
@@ -2363,7 +2363,7 @@ private void OnTransformParentChanged()
                 }
                 else
                 {
-                    foreach (var clientId in NetworkManager.ConnectedClientsIds)
+                    foreach (var clientId in NetworkManager.ConnectionManager.ConnectedClientIds)
                     {
                         if (clientId == NetworkManager.ServerClientId)
                         {
@@ -2382,7 +2382,7 @@ private void OnTransformParentChanged()
                     var maxCount = NetworkManager.ConnectedClientsIds.Count;
                     ulong* clientIds = stackalloc ulong[maxCount];
                     int idx = 0;
-                    foreach (var clientId in NetworkManager.ConnectedClientsIds)
+                    foreach (var clientId in NetworkManager.ConnectionManager.ConnectedClientIds)
                     {
                         if (clientId == NetworkManager.ServerClientId)
                         {

com.unity.netcode.gameobjects/Runtime/Messaging/Messages/ChangeOwnershipMessage.cs

@@ -250,8 +250,9 @@ public void Handle(ref NetworkContext context)
                 }
                 else
                 {
-                    foreach (var clientId in clientList)
+                    for (int i = 0; i < clientList.Count; i++)
                     {
+                        var clientId = clientList[i];
                         if (clientId == networkManager.LocalClientId)
                         {
                             continue;

com.unity.netcode.gameobjects/Runtime/Messaging/Messages/CreateObjectMessage.cs

@@ -247,9 +247,9 @@ internal static void CreateObject(ref NetworkManager networkManager, ulong sende
                     var clientList = hasObserverIdList && !networkObject.IsPlayerObject ? observerIds : networkManager.ConnectedClientsIds;
 
                     // Update the observers for this instance
-                    foreach (var clientId in clientList)
+                    for (int i = 0; i < clientList.Count; i++)
                     {
-                        networkObject.Observers.Add(clientId);
+                        networkObject.Observers.Add(clientList[i]);
                     }
 
                     // Mock CMB Service and forward to all clients

com.unity.netcode.gameobjects/Runtime/Messaging/Messages/DestroyObjectMessage.cs

@@ -189,7 +189,7 @@ private void HandleDAHostForwardMessage(ulong senderId, ref NetworkManager netwo
                 DeferredDespawnTick = DeferredDespawnTick,
             };
             var ownerClientId = networkObject == null ? senderId : networkObject.OwnerClientId;
-            var clientIds = networkObject == null ? networkManager.ConnectedClientsIds.ToList() : networkObject.Observers.ToList();
+            var clientIds = networkObject == null ? networkManager.ConnectionManager.ConnectedClientIds : networkObject.Observers.ToList();
 
             foreach (var clientId in clientIds)
             {

com.unity.netcode.gameobjects/Runtime/Messaging/Messages/NetworkVariableDeltaMessage.cs

@@ -228,7 +228,7 @@ public void Handle(ref NetworkContext context)
                     if (isServerAndDeltaForwarding)
                     {
                         m_ForwardUpdates = new Dictionary<ulong, List<int>>();
-                        foreach (var clientId in networkManager.ConnectedClientsIds)
+                        foreach (var clientId in networkManager.ConnectionManager.ConnectedClientIds)
                         {
                             if (clientId == context.SenderId || clientId == networkManager.LocalClientId || !networkObject.Observers.Contains(clientId))
                             {

com.unity.netcode.gameobjects/Runtime/Messaging/RpcTargets/BaseRpcTarget.cs

@@ -11,6 +11,8 @@ public abstract class BaseRpcTarget : IDisposable
         /// The <see cref="NetworkManager"/> instance which can be used to handle sending and receiving the specific target(s)
         /// </summary>
         protected NetworkManager m_NetworkManager;
+
+        internal NetworkConnectionManager ConnectionManager;
         private bool m_Locked;
 
         internal void Lock()
@@ -26,6 +28,7 @@ internal void Unlock()
         internal BaseRpcTarget(NetworkManager manager)
         {
             m_NetworkManager = manager;
+            ConnectionManager = m_NetworkManager.ConnectionManager;
         }
 
         /// <summary>

com.unity.netcode.gameobjects/Runtime/Messaging/RpcTargets/NotAuthorityRpcTarget.cs

@@ -40,7 +40,7 @@ internal override void Send(NetworkBehaviour behaviour, ref RpcMessage message,
                 }
                 else
                 {
-                    foreach (var clientId in m_NetworkManager.ConnectedClientsIds)
+                    foreach (var clientId in ConnectionManager.ConnectedClientIds)
                     {
                         if (clientId == behaviour.OwnerClientId || !networkObject.Observers.Contains(clientId))
                         {