From 2e10d776e9bc4e80323a3bb82f62337e21b36971 Mon Sep 17 00:00:00 2001
From: Wojtek Figat <wojtek@figat.pl>
Date: Thu, 19 Jun 2025 14:04:06 +0200
Subject: [PATCH] Optimize updating actor rendering entry with better thread
 locking that support async writes on actor update

---
 Source/Engine/Level/Scene/SceneRendering.cpp       | 14 +++++++-------
 Source/Engine/Level/Scene/SceneRendering.h         |  4 ++--
 Source/Engine/Threading/ConcurrentSystemLocker.cpp |  2 +-
 3 files changed, 10 insertions(+), 10 deletions(-)

diff --git a/Source/Engine/Level/Scene/SceneRendering.cpp b/Source/Engine/Level/Scene/SceneRendering.cpp
index fe2bc310f..4a88703ae 100644
--- a/Source/Engine/Level/Scene/SceneRendering.cpp
+++ b/Source/Engine/Level/Scene/SceneRendering.cpp
@@ -43,7 +43,7 @@ FORCE_INLINE bool FrustumsListCull(const BoundingSphere& bounds, const Array<Bou
 void SceneRendering::Draw(RenderContextBatch& renderContextBatch, DrawCategory category)
 {
     PROFILE_MEM(Graphics);
-    ScopeLock lock(Locker);
+    ConcurrentSystemLocker::ReadScope lock(Locker);
     if (category == PreRender)
     {
         // Register scene
@@ -51,12 +51,12 @@ void SceneRendering::Draw(RenderContextBatch& renderContextBatch, DrawCategory c
             renderContext.List->Scenes.Add(this);
 
         // Add additional lock during scene rendering (prevents any Actors cache modifications on content streaming threads - eg. when model residency changes)
-        Locker.Lock();
+        Locker.Begin(false);
     }
     else if (category == PostRender)
     {
         // Release additional lock
-        Locker.Unlock();
+        Locker.End(false);
     }
     auto& view = renderContextBatch.GetMainContext().View;
     auto& list = Actors[(int32)category];
@@ -127,7 +127,7 @@ void SceneRendering::CollectPostFxVolumes(RenderContext& renderContext)
 
 void SceneRendering::Clear()
 {
-    ScopeLock lock(Locker);
+    ConcurrentSystemLocker::WriteScope lock(Locker);
     for (auto* listener : _listeners)
     {
         listener->OnSceneRenderingClear(this);
@@ -149,7 +149,7 @@ void SceneRendering::AddActor(Actor* a, int32& key)
         return;
     PROFILE_MEM(Graphics);
     const int32 category = a->_drawCategory;
-    ScopeLock lock(Locker);
+    ConcurrentSystemLocker::WriteScope lock(Locker);
     auto& list = Actors[category];
     if (FreeActors[category].HasItems())
     {
@@ -174,7 +174,7 @@ void SceneRendering::AddActor(Actor* a, int32& key)
 void SceneRendering::UpdateActor(Actor* a, int32& key, ISceneRenderingListener::UpdateFlags flags)
 {
     const int32 category = a->_drawCategory;
-    ScopeLock lock(Locker);
+    ConcurrentSystemLocker::ReadScope lock(Locker); // Read-access only as list doesn't get resized (like Add/Remove do) so allow updating actors from different threads at once
     auto& list = Actors[category];
     if (list.Count() <= key) // Ignore invalid key softly
         return;
@@ -193,7 +193,7 @@ void SceneRendering::UpdateActor(Actor* a, int32& key, ISceneRenderingListener::
 void SceneRendering::RemoveActor(Actor* a, int32& key)
 {
     const int32 category = a->_drawCategory;
-    ScopeLock lock(Locker);
+    ConcurrentSystemLocker::WriteScope lock(Locker);
     auto& list = Actors[category];
     if (list.Count() > key) // Ignore invalid key softly (eg. list after batch clear during scene unload)
     {
diff --git a/Source/Engine/Level/Scene/SceneRendering.h b/Source/Engine/Level/Scene/SceneRendering.h
index b24dcdfa9..59f997f6b 100644
--- a/Source/Engine/Level/Scene/SceneRendering.h
+++ b/Source/Engine/Level/Scene/SceneRendering.h
@@ -7,7 +7,7 @@
 #include "Engine/Core/Math/BoundingSphere.h"
 #include "Engine/Core/Math/BoundingFrustum.h"
 #include "Engine/Level/Actor.h"
-#include "Engine/Platform/CriticalSection.h"
+#include "Engine/Threading/ConcurrentSystemLocker.h"
 
 class SceneRenderTask;
 class SceneRendering;
@@ -102,7 +102,7 @@ public:
     Array<DrawActor> Actors[MAX];
     Array<int32> FreeActors[MAX];
     Array<IPostFxSettingsProvider*> PostFxProviders;
-    CriticalSection Locker;
+    ConcurrentSystemLocker Locker;
 
 private:
 #if USE_EDITOR
diff --git a/Source/Engine/Threading/ConcurrentSystemLocker.cpp b/Source/Engine/Threading/ConcurrentSystemLocker.cpp
index c8569b119..f8eab96d9 100644
--- a/Source/Engine/Threading/ConcurrentSystemLocker.cpp
+++ b/Source/Engine/Threading/ConcurrentSystemLocker.cpp
@@ -18,7 +18,7 @@ RETRY:
     {
         // Someone else is doing opposite operation so wait for it's end
         // TODO: use ConditionVariable+CriticalSection to prevent active-waiting
-        Platform::Sleep(1);
+        Platform::Sleep(0);
         goto RETRY;
     }