From 78d519cb9a71ab42a506c0f5018b6d417f2bf426 Mon Sep 17 00:00:00 2001
From: Wojtek Figat <wojtek@figat.pl>
Date: Sun, 29 Jun 2025 19:16:41 +0200
Subject: [PATCH] Fix `ConcurrentSystemLocker` to have exclusive lock as an
 option

---
 Source/Engine/Level/Scene/SceneRendering.cpp           | 6 +++---
 Source/Engine/Renderer/GlobalSignDistanceFieldPass.cpp | 8 +++++---
 Source/Engine/Threading/ConcurrentSystemLocker.cpp     | 6 +++---
 Source/Engine/Threading/ConcurrentSystemLocker.h       | 6 +++---
 4 files changed, 14 insertions(+), 12 deletions(-)

diff --git a/Source/Engine/Level/Scene/SceneRendering.cpp b/Source/Engine/Level/Scene/SceneRendering.cpp
index 4a88703ae..e55dbd43f 100644
--- a/Source/Engine/Level/Scene/SceneRendering.cpp
+++ b/Source/Engine/Level/Scene/SceneRendering.cpp
@@ -127,7 +127,7 @@ void SceneRendering::CollectPostFxVolumes(RenderContext& renderContext)
 
 void SceneRendering::Clear()
 {
-    ConcurrentSystemLocker::WriteScope lock(Locker);
+    ConcurrentSystemLocker::WriteScope lock(Locker, true);
     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;
-    ConcurrentSystemLocker::WriteScope lock(Locker);
+    ConcurrentSystemLocker::WriteScope lock(Locker, true);
     auto& list = Actors[category];
     if (FreeActors[category].HasItems())
     {
@@ -193,7 +193,7 @@ void SceneRendering::UpdateActor(Actor* a, int32& key, ISceneRenderingListener::
 void SceneRendering::RemoveActor(Actor* a, int32& key)
 {
     const int32 category = a->_drawCategory;
-    ConcurrentSystemLocker::WriteScope lock(Locker);
+    ConcurrentSystemLocker::WriteScope lock(Locker, true);
     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/Renderer/GlobalSignDistanceFieldPass.cpp b/Source/Engine/Renderer/GlobalSignDistanceFieldPass.cpp
index 56dd196a5..e0d227b6b 100644
--- a/Source/Engine/Renderer/GlobalSignDistanceFieldPass.cpp
+++ b/Source/Engine/Renderer/GlobalSignDistanceFieldPass.cpp
@@ -396,7 +396,7 @@ public:
     {
         if (GLOBAL_SDF_ACTOR_IS_STATIC(a) && ObjectTypes.Contains(a->GetTypeHandle()))
         {
-            ConcurrentSystemLocker::WriteScope lock(Locker);
+            ConcurrentSystemLocker::WriteScope lock(Locker, true);
             OnSceneRenderingDirty(a->GetBox());
         }
     }
@@ -405,7 +405,7 @@ public:
     {
         if (GLOBAL_SDF_ACTOR_IS_STATIC(a) && ObjectTypes.Contains(a->GetTypeHandle()))
         {
-            ConcurrentSystemLocker::WriteScope lock(Locker);
+            ConcurrentSystemLocker::WriteScope lock(Locker, true);
             OnSceneRenderingDirty(BoundingBox::FromSphere(prevBounds));
             OnSceneRenderingDirty(a->GetBox());
         }
@@ -415,13 +415,14 @@ public:
     {
         if (GLOBAL_SDF_ACTOR_IS_STATIC(a) && ObjectTypes.Contains(a->GetTypeHandle()))
         {
-            ConcurrentSystemLocker::WriteScope lock(Locker);
+            ConcurrentSystemLocker::WriteScope lock(Locker, true);
             OnSceneRenderingDirty(a->GetBox());
         }
     }
 
     void OnSceneRenderingClear(SceneRendering* scene) override
     {
+        ConcurrentSystemLocker::WriteScope lock(Locker, true);
         for (auto& cascade : Cascades)
             cascade.StaticChunks.Clear();
     }
@@ -719,6 +720,7 @@ bool GlobalSignDistanceFieldPass::Render(RenderContext& renderContext, GPUContex
     }
     sdfData.LastFrameUsed = currentFrame;
     PROFILE_GPU_CPU("Global SDF");
+    ConcurrentSystemLocker::WriteScope lock(sdfData.Locker);
 
     // Setup options
     int32 resolution, cascadesCount, resolutionMip;
diff --git a/Source/Engine/Threading/ConcurrentSystemLocker.cpp b/Source/Engine/Threading/ConcurrentSystemLocker.cpp
index c8debb561..d936f8307 100644
--- a/Source/Engine/Threading/ConcurrentSystemLocker.cpp
+++ b/Source/Engine/Threading/ConcurrentSystemLocker.cpp
@@ -8,7 +8,7 @@ ConcurrentSystemLocker::ConcurrentSystemLocker()
     _counters[0] = _counters[1] = 0;
 }
 
-void ConcurrentSystemLocker::Begin(bool write)
+void ConcurrentSystemLocker::Begin(bool write, bool exclusively)
 {
     volatile int64* thisCounter = &_counters[write];
     volatile int64* otherCounter = &_counters[!write];
@@ -22,8 +22,8 @@ RETRY:
         goto RETRY;
     }
 
-    // Writers have to check themselves to (one write at the same time - just like a mutex)
-    if (write && Platform::AtomicRead(thisCounter) != 0)
+    // Writers might want to check themselves for a single writer at the same time - just like a mutex
+    if (exclusively && Platform::AtomicRead(thisCounter) != 0)
     {
         // Someone else is doing opposite operation so wait for it's end
         Platform::Sleep(0);
diff --git a/Source/Engine/Threading/ConcurrentSystemLocker.h b/Source/Engine/Threading/ConcurrentSystemLocker.h
index dd214a308..031b7e685 100644
--- a/Source/Engine/Threading/ConcurrentSystemLocker.h
+++ b/Source/Engine/Threading/ConcurrentSystemLocker.h
@@ -17,7 +17,7 @@ public:
     NON_COPYABLE(ConcurrentSystemLocker);
     ConcurrentSystemLocker();
 
-    void Begin(bool write);
+    void Begin(bool write, bool exclusively = false);
     void End(bool write);
 
 public:
@@ -26,10 +26,10 @@ public:
     {
         NON_COPYABLE(Scope);
 
-        Scope(ConcurrentSystemLocker& locker)
+        Scope(ConcurrentSystemLocker& locker, bool exclusively = false)
             : _locker(locker)
         {
-            _locker.Begin(Write);
+            _locker.Begin(Write, exclusively);
         }
 
         ~Scope()