From 937d369856018fef09e03e591f9e8e3f6c9efc37 Mon Sep 17 00:00:00 2001
From: Wojtek Figat <wojtek@figat.pl>
Date: Tue, 18 Feb 2025 23:27:49 +0100
Subject: [PATCH] Fix crash in particles system when assets gets
 loading/unloaded while async jobs are active

---
 Source/Engine/Animations/Animations.cpp             |  2 +-
 Source/Engine/Particles/ParticleEmitter.cpp         |  5 ++++-
 Source/Engine/Particles/ParticleEmitterFunction.cpp |  6 +++++-
 Source/Engine/Particles/Particles.cpp               | 12 ++++++++++++
 Source/Engine/Particles/Particles.h                 |  4 ++++
 5 files changed, 26 insertions(+), 3 deletions(-)

diff --git a/Source/Engine/Animations/Animations.cpp b/Source/Engine/Animations/Animations.cpp
index cbaf78883..b0397f287 100644
--- a/Source/Engine/Animations/Animations.cpp
+++ b/Source/Engine/Animations/Animations.cpp
@@ -120,7 +120,7 @@ void AnimationsSystem::Execute(TaskGraph* graph)
         return;
     Active = true;
 
-    // Ensure no animation assets it being reloading/modified before running async update
+    // Ensure no animation assets can be reloaded/modified during async update
     Animations::SystemLocker.Begin(false);
 
     // Setup data for async update
diff --git a/Source/Engine/Particles/ParticleEmitter.cpp b/Source/Engine/Particles/ParticleEmitter.cpp
index 570b026c6..66a19ea45 100644
--- a/Source/Engine/Particles/ParticleEmitter.cpp
+++ b/Source/Engine/Particles/ParticleEmitter.cpp
@@ -72,6 +72,8 @@ namespace
 
 Asset::LoadResult ParticleEmitter::load()
 {
+    ConcurrentSystemLocker::WriteScope systemScope(Particles::SystemLocker);
+
     // Load the graph
     const auto surfaceChunk = GetChunk(SHADER_FILE_CHUNK_VISJECT_SURFACE);
     if (!surfaceChunk)
@@ -287,6 +289,7 @@ Asset::LoadResult ParticleEmitter::load()
 
 void ParticleEmitter::unload(bool isReloading)
 {
+    ConcurrentSystemLocker::WriteScope systemScope(Particles::SystemLocker);
 #if COMPILE_WITH_SHADER_COMPILER
     UnregisterForShaderReloads(this);
 #endif
@@ -389,7 +392,7 @@ bool ParticleEmitter::SaveSurface(BytesContainer& data)
         LOG(Error, "Asset loading failed. Cannot save it.");
         return true;
     }
-
+    ConcurrentSystemLocker::WriteScope systemScope(Particles::SystemLocker);
     ScopeLock lock(Locker);
 
     // Release all chunks
diff --git a/Source/Engine/Particles/ParticleEmitterFunction.cpp b/Source/Engine/Particles/ParticleEmitterFunction.cpp
index eae85e351..7931fb3ab 100644
--- a/Source/Engine/Particles/ParticleEmitterFunction.cpp
+++ b/Source/Engine/Particles/ParticleEmitterFunction.cpp
@@ -1,6 +1,7 @@
 // Copyright (c) 2012-2024 Wojciech Figat. All rights reserved.
 
 #include "ParticleEmitterFunction.h"
+#include "Particles.h"
 #include "Engine/Core/Log.h"
 #include "Engine/Serialization/MemoryReadStream.h"
 #include "Engine/Threading/Threading.h"
@@ -39,6 +40,8 @@ ParticleEmitterFunction::ParticleEmitterFunction(const SpawnParams& params, cons
 
 Asset::LoadResult ParticleEmitterFunction::load()
 {
+    ConcurrentSystemLocker::WriteScope systemScope(Particles::SystemLocker);
+
     // Load graph
     const auto surfaceChunk = GetChunk(0);
     if (!surfaceChunk || !surfaceChunk->IsLoaded())
@@ -90,6 +93,7 @@ Asset::LoadResult ParticleEmitterFunction::load()
 
 void ParticleEmitterFunction::unload(bool isReloading)
 {
+    ConcurrentSystemLocker::WriteScope systemScope(Particles::SystemLocker);
     Graph.Clear();
 #if COMPILE_WITH_PARTICLE_GPU_GRAPH
     GraphGPU.Clear();
@@ -190,7 +194,7 @@ bool ParticleEmitterFunction::SaveSurface(BytesContainer& data)
         LOG(Error, "Asset loading failed. Cannot save it.");
         return true;
     }
-
+    ConcurrentSystemLocker::WriteScope systemScope(Particles::SystemLocker);
     ScopeLock lock(Locker);
 
     // Set Visject Surface data
diff --git a/Source/Engine/Particles/Particles.cpp b/Source/Engine/Particles/Particles.cpp
index f97325248..f229968a3 100644
--- a/Source/Engine/Particles/Particles.cpp
+++ b/Source/Engine/Particles/Particles.cpp
@@ -111,6 +111,7 @@ namespace ParticleManagerImpl
 using namespace ParticleManagerImpl;
 
 TaskGraphSystem* Particles::System = nullptr;
+ConcurrentSystemLocker Particles::SystemLocker;
 bool Particles::EnableParticleBufferPooling = true;
 float Particles::ParticleBufferRecycleTimeout = 10.0f;
 
@@ -139,6 +140,8 @@ class ParticlesSystem : public TaskGraphSystem
 {
 public:
     float DeltaTime, UnscaledDeltaTime, Time, UnscaledTime;
+    bool Active;
+
     void Job(int32 index);
     void Execute(TaskGraph* graph) override;
     void PostExecute(TaskGraph* graph) override;
@@ -1390,6 +1393,10 @@ void ParticlesSystem::Execute(TaskGraph* graph)
 {
     if (UpdateList.Count() == 0)
         return;
+    Active = true;
+
+    // Ensure no particle assets can be reloaded/modified during async update
+    Particles::SystemLocker.Begin(false);
 
     // Setup data for async update
     const auto& tickData = Time::Update;
@@ -1406,8 +1413,13 @@ void ParticlesSystem::Execute(TaskGraph* graph)
 
 void ParticlesSystem::PostExecute(TaskGraph* graph)
 {
+    if (!Active)
+        return;
     PROFILE_CPU_NAMED("Particles.PostExecute");
 
+    // Cleanup
+    Particles::SystemLocker.End(false);
+    Active = false;
     UpdateList.Clear();
 
 #if COMPILE_WITH_GPU_PARTICLES
diff --git a/Source/Engine/Particles/Particles.h b/Source/Engine/Particles/Particles.h
index b3effdeb1..b493b19a4 100644
--- a/Source/Engine/Particles/Particles.h
+++ b/Source/Engine/Particles/Particles.h
@@ -3,6 +3,7 @@
 #pragma once
 
 #include "Engine/Scripting/ScriptingType.h"
+#include "Engine/Threading/ConcurrentSystemLocker.h"
 
 class TaskGraphSystem;
 struct RenderContext;
@@ -27,6 +28,9 @@ API_CLASS(Static) class FLAXENGINE_API Particles
     /// </summary>
     API_FIELD(ReadOnly) static TaskGraphSystem* System;
 
+    // Data access locker for animations data.
+    static ConcurrentSystemLocker SystemLocker;
+
 public:
     /// <summary>
     /// Updates the effect during next particles simulation tick.