perf: remove allocations during syncvar sync (#946)

Assets/Mirror/Runtime/NetworkIdentity.cs

@@ -573,28 +573,21 @@ bool OnSerializeSafely(NetworkBehaviour comp, NetworkWriter writer, bool initial
             return result;
         }
 
-        // OnSerializeAllSafely is in hot path. caching the writer is really
-        // worth it to avoid large amounts of allocations.
-        static NetworkWriter onSerializeWriter = new NetworkWriter();
-
         // serialize all components (or only dirty ones if not initial state)
-        // -> returns serialized data of everything dirty,  null if nothing was dirty
-        internal byte[] OnSerializeAllSafely(bool initialState)
+        // -> returns true if something was written
+        internal bool OnSerializeAllSafely(bool initialState, NetworkWriter writer)
         {
-            // reset cached writer length and position
-            onSerializeWriter.SetLength(0);
-
             if (networkBehavioursCache.Length > 64)
             {
                 Debug.LogError("Only 64 NetworkBehaviour components are allowed for NetworkIdentity: " + name + " because of the dirtyComponentMask");
-                return null;
+                return false;
             }
             ulong dirtyComponentsMask = GetDirtyMask(networkBehavioursCache, initialState);
 
             if (dirtyComponentsMask == 0L)
-                return null;
+                return false;
 
-            onSerializeWriter.WritePackedUInt64(dirtyComponentsMask); // WritePacked64 so we don't write full 8 bytes if we don't have to
+            writer.WritePackedUInt64(dirtyComponentsMask); // WritePacked64 so we don't write full 8 bytes if we don't have to
 
             foreach (NetworkBehaviour comp in networkBehavioursCache)
             {
@@ -605,7 +598,7 @@ internal byte[] OnSerializeAllSafely(bool initialState)
                 {
                     // serialize the data
                     if (LogFilter.Debug) Debug.Log("OnSerializeAllSafely: " + name + " -> " + comp.GetType() + " initial=" + initialState);
-                    OnSerializeSafely(comp, onSerializeWriter, initialState);
+                    OnSerializeSafely(comp, writer, initialState);
 
                     // Clear dirty bits only if we are synchronizing data and not sending a spawn message.
                     // This preserves the behavior in HLAPI
@@ -616,7 +609,7 @@ internal byte[] OnSerializeAllSafely(bool initialState)
                 }
             }
 
-            return onSerializeWriter.ToArray();
+            return true;
         }
 
         ulong GetDirtyMask(NetworkBehaviour[] components, bool initialState)
@@ -1037,17 +1030,18 @@ internal void MirrorUpdate()
             if (observers == null || observers.Count == 0)
                 return;
 
+            NetworkWriter writer = NetworkWriterPool.GetWriter();
             // serialize all the dirty components and send (if any were dirty)
-            byte[] payload = OnSerializeAllSafely(false);
-            if (payload != null)
+            if (OnSerializeAllSafely(false, writer))
             {
                 // populate cached UpdateVarsMessage and send
                 varsMessage.netId = netId;
                 // segment to avoid reader allocations.
                 // (never null because of our above check)
-                varsMessage.payload = new ArraySegment<byte>(payload);
+                varsMessage.payload = writer.ToArraySegment();
                 NetworkServer.SendToReady(this, varsMessage);
             }
+            NetworkWriterPool.Recycle(writer);
         }
     }
 }

Assets/Mirror/Runtime/NetworkServer.cs

@@ -836,13 +836,20 @@ internal static void SendSpawnMessage(NetworkIdentity identity, NetworkConnectio
 
             if (LogFilter.Debug) Debug.Log("Server SendSpawnMessage: name=" + identity.name + " sceneId=" + identity.sceneId.ToString("X") + " netid=" + identity.netId); // for easier debugging
 
-            // serialize all components with initialState = true
-            // (can be null if has none)
-            byte[] serialized = identity.OnSerializeAllSafely(true);
+            NetworkWriter writer = NetworkWriterPool.GetWriter();
+
+
 
             // convert to ArraySegment to avoid reader allocations
             // (need to handle null case too)
-            ArraySegment<byte> segment = serialized != null ? new ArraySegment<byte>(serialized) : default;
+            ArraySegment<byte> segment = default;
+
+            // serialize all components with initialState = true
+            // (can be null if has none)
+            if (identity.OnSerializeAllSafely(true, writer))
+            {
+                segment = writer.ToArraySegment();
+            }
 
             // 'identity' is a prefab that should be spawned
             if (identity.sceneId == 0)
@@ -896,6 +903,8 @@ internal static void SendSpawnMessage(NetworkIdentity identity, NetworkConnectio
                     SendToReady(identity, msg);
                 }
             }
+
+            NetworkWriterPool.Recycle(writer);
         }
 
         public static void DestroyPlayerForConnection(NetworkConnection conn)