From 4241eb9c2cec0d525bf0b3ff5ea2c616268e65cf Mon Sep 17 00:00:00 2001
From: amzn-sean <75276488+amzn-sean@users.noreply.github.com>
Date: Wed, 9 Jun 2021 17:42:16 +0100
Subject: [PATCH] fix crash in ragdoll (#1210)

---
 .../Source/PhysXCharacters/API/Ragdoll.cpp    | 22 ++++++++++++++++---
 .../Code/Source/PhysXCharacters/API/Ragdoll.h |  2 ++
 2 files changed, 21 insertions(+), 3 deletions(-)

diff --git a/Gems/PhysX/Code/Source/PhysXCharacters/API/Ragdoll.cpp b/Gems/PhysX/Code/Source/PhysXCharacters/API/Ragdoll.cpp
index 02ebe7281c..4725212a9d 100644
--- a/Gems/PhysX/Code/Source/PhysXCharacters/API/Ragdoll.cpp
+++ b/Gems/PhysX/Code/Source/PhysXCharacters/API/Ragdoll.cpp
@@ -13,6 +13,7 @@
 #include <PhysX_precompiled.h>
 #include <AzCore/Serialization/EditContext.h>
 #include <AzCore/std/smart_ptr/make_shared.h>
+#include <AzCore/std/parallel/scoped_lock.h>
 #include <AzFramework/Physics/PhysicsScene.h>
 #include <AzFramework/Physics/PhysicsSystem.h>
 #include <AzFramework/Physics/SystemBus.h>
@@ -40,6 +41,8 @@ namespace PhysX
     } // namespace Internal
 
     // PhysX::Ragdoll
+    /*static*/ AZStd::mutex Ragdoll::m_sceneEventMutex;
+
     void Ragdoll::Reflect(AZ::ReflectContext* context)
     {
         AZ::SerializeContext* serializeContext = azrtti_cast<AZ::SerializeContext*>(context);
@@ -114,7 +117,10 @@ namespace PhysX
 
     Ragdoll::~Ragdoll()
     {
-        m_sceneStartSimHandler.Disconnect();
+        {
+            AZStd::scoped_lock lock(m_sceneEventMutex);
+            m_sceneStartSimHandler.Disconnect();
+        }
 
         m_nodes.clear(); //the nodes destructor will remove the simulated body from the scene.
     }
@@ -212,7 +218,13 @@ namespace PhysX
             }
         }
 
-        sceneInterface->RegisterSceneSimulationStartHandler(m_sceneOwner, m_sceneStartSimHandler);
+        // the handler is also connected in EnableSimulationQueued(),
+        // which will call this function, so if called from that path dont connect here.
+        if (!m_sceneStartSimHandler.IsConnected()) 
+        {
+            AZStd::scoped_lock lock(m_sceneEventMutex);
+            sceneInterface->RegisterSceneSimulationStartHandler(m_sceneOwner, m_sceneStartSimHandler);
+        }
         sceneInterface->EnableSimulationOfBody(m_sceneOwner, m_bodyHandle);
     }
 
@@ -225,6 +237,7 @@ namespace PhysX
 
         if (auto* sceneInterface = AZ::Interface<AzPhysics::SceneInterface>::Get())
         {
+            AZStd::scoped_lock lock(m_sceneEventMutex);
             sceneInterface->RegisterSceneSimulationStartHandler(m_sceneOwner, m_sceneStartSimHandler);
         }
 
@@ -244,7 +257,10 @@ namespace PhysX
             return;
         }
 
-        m_sceneStartSimHandler.Disconnect();
+        {
+            AZStd::scoped_lock lock(m_sceneEventMutex);
+            m_sceneStartSimHandler.Disconnect();
+        }
 
         physx::PxScene* pxScene = Internal::GetPxScene(m_sceneOwner);
         const size_t numNodes = m_nodes.size();
diff --git a/Gems/PhysX/Code/Source/PhysXCharacters/API/Ragdoll.h b/Gems/PhysX/Code/Source/PhysXCharacters/API/Ragdoll.h
index 7182a3a44c..006ce5878b 100644
--- a/Gems/PhysX/Code/Source/PhysXCharacters/API/Ragdoll.h
+++ b/Gems/PhysX/Code/Source/PhysXCharacters/API/Ragdoll.h
@@ -12,6 +12,7 @@
 
 #pragma once
 
+#include <AzCore/std/parallel/mutex.h>
 #include <AzFramework/Physics/RagdollPhysicsBus.h>
 #include <AzFramework/Physics/Ragdoll.h>
 #include <AzFramework/Physics/Common/PhysicsEvents.h>
@@ -84,5 +85,6 @@ namespace PhysX
         bool m_queuedDisableSimulation = false;
 
         AzPhysics::SceneEvents::OnSceneSimulationStartHandler m_sceneStartSimHandler;
+        static AZStd::mutex m_sceneEventMutex;
     };
 } // namespace PhysX