From 62c2008cbcb1f395a4e3c20f19263187381b0caa Mon Sep 17 00:00:00 2001
From: Wojtek Figat <wojtek@figat.pl>
Date: Fri, 22 Sep 2023 12:50:50 +0200
Subject: [PATCH] Fix crash in C# `JobSystem.Dispatch` due to GC collecting
 Delegate object

---
 Source/Engine/Engine/NativeInterop.cs              | 14 ++++++++++++++
 .../Bindings/BindingsGenerator.CSharp.cs           |  2 +-
 2 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/Source/Engine/Engine/NativeInterop.cs b/Source/Engine/Engine/NativeInterop.cs
index dfef614b3..e0ef84a61 100644
--- a/Source/Engine/Engine/NativeInterop.cs
+++ b/Source/Engine/Engine/NativeInterop.cs
@@ -148,6 +148,20 @@ namespace FlaxEngine.Interop
             NativeMemory.AlignedFree(ptr);
         }
 
+        /// <summary>
+        /// Converts a delegate into a function pointer that is callable from unmanaged code via <see cref="Marshal.GetFunctionPointerForDelegate{TDelegate}"/> but cached <paramref name="d"/> delegate to prevent collecting it by GC.
+        /// </summary>
+        /// <typeparam name="TDelegate">The type of delegate to convert.</typeparam>
+        /// <param name="d">The delegate to be passed to unmanaged code.</param>
+        /// <returns>A value that can be passed to unmanaged code, which, in turn, can use it to call the underlying managed delegate.</returns>
+        public static IntPtr GetFunctionPointerForDelegate<TDelegate>(TDelegate d) where TDelegate : notnull
+        {
+            // Example use-case: C# script runs actions via JobSystem.Dispatch which causes crash due to GC collecting Delegate object
+            ManagedHandle.Alloc(d, GCHandleType.Weak);
+
+            return Marshal.GetFunctionPointerForDelegate<TDelegate>(d);
+        }
+
         /// <summary>
         /// Converts array of GC Handles from native runtime to managed array.
         /// </summary>
diff --git a/Source/Tools/Flax.Build/Bindings/BindingsGenerator.CSharp.cs b/Source/Tools/Flax.Build/Bindings/BindingsGenerator.CSharp.cs
index 6a9aa7669..3685cb271 100644
--- a/Source/Tools/Flax.Build/Bindings/BindingsGenerator.CSharp.cs
+++ b/Source/Tools/Flax.Build/Bindings/BindingsGenerator.CSharp.cs
@@ -464,7 +464,7 @@ namespace Flax.Build.Bindings
                 return "FlaxEngine.Object.GetUnmanagedPtr({0})";
             case "Function":
                 // delegate
-                return "Marshal.GetFunctionPointerForDelegate({0})";
+                return "NativeInterop.GetFunctionPointerForDelegate({0})";
             default:
                 var apiType = FindApiTypeInfo(buildData, typeInfo, caller);
                 if (apiType != null)