Fix crash in animations system when assets gets loading/unloaded while async jobs are active

#2974

Source/Engine/Threading/ConcurrentSystemLocker.h

@@ -0,0 +1,46 @@
+// Copyright (c) 2012-2024 Wojciech Figat. All rights reserved.
+
+#pragma once
+
+#include "Engine/Core/Core.h"
+#include "Engine/Core/Types/BaseTypes.h"
+
+/// <summary>
+/// Utility for guarding system data access from different threads depending on the resources usage (eg. block read on write).
+/// </summary>
+struct ConcurrentSystemLocker
+{
+private:
+    volatile int64 _counters[2];
+
+public:
+    NON_COPYABLE(ConcurrentSystemLocker);
+    ConcurrentSystemLocker();
+
+    void Begin(bool write);
+    void End(bool write);
+
+public:
+    template<bool Write>
+    struct Scope
+    {
+        NON_COPYABLE(Scope);
+
+        Scope(ConcurrentSystemLocker& locker)
+            : _locker(locker)
+        {
+            _locker.Begin(Write);
+        }
+
+        ~Scope()
+        {
+            _locker.End(Write);
+        }
+
+    private:
+        ConcurrentSystemLocker& _locker;
+    };
+
+    typedef Scope<false> ReadScope;
+    typedef Scope<true> WriteScope;
+};