Feature Request Full support for C# 9 FunctionPointer (delegate* unmanaged[Cdecl]).

Code (CSharp):

1. using System.Runtime.InteropServices;
2. using AOT;
3. using Unity.Burst;
4. using UnityEngine;
5.  
6. [BurstCompile]
7. public unsafe class FunctionPointerC9Burst : MonoBehaviour {
8.     [UnmanagedFunctionPointer(CallingConvention.Cdecl)]
9.     public delegate int UnmanagedDelegate(int value);
10.  
11.     [MonoPInvokeCallback(typeof(UnmanagedDelegate))]
12.     private static int Increment(int value) => ++value;
13.  
14.     private static readonly delegate* unmanaged[Cdecl]<int, int> c9Ptr
15.         = (delegate* unmanaged[Cdecl]<int, int>) Marshal.GetFunctionPointerForDelegate((UnmanagedDelegate) Increment);
16.  
17.     void Start() {
18.         SuccessfullyCompiled(c9Ptr, 0);
19.         CompilationFailsAndFallbackToManagedCallback(c9Ptr, 0);
20.     }
21.  
22.     [BurstCompile]
23.     static void SuccessfullyCompiled(void* unmanagedCallback, int value) {
24.         Debug.Log($"Value: {((delegate* unmanaged[Cdecl]<int, int>) unmanagedCallback)(value)}, RunOnBurst ? {RunOnBurst.IsTrue}");
25.     }
26.  
27.     [BurstCompile]
28.     static void CompilationFailsAndFallbackToManagedCallback(delegate* unmanaged[Cdecl]<int, int> unmanagedCallback, int value) {
29.         Debug.Log($"Value: {unmanagedCallback(value)}, RunOnBurst ? {RunOnBurst.IsTrue}");
30.     }
31. }
32.  
33. public static class RunOnBurst {
34.     public static bool IsTrue {
35.         get {
36.             var runOnBurst = true;
37.             Detector(ref runOnBurst);
38.             return runOnBurst;
39.         }
40.     }
41.     [BurstDiscard] static void Detector(ref bool runOnBurst) => runOnBurst = false;
42. }

If I pass a c#9 function pointer to the burst code, it does not compile correctly. If I cast the function pointer to void*, it compiles successfully, and it works fine on the actual Android IL2CPP device, so I think it is failing to get the method signature correctly.

Also both JobSystem and IL2CPP fail to recognize the C#9 pointer signature (delegate* unmanaged[Cdecl]<SomeType>), resulting in runtime or compilation errors.

However, if I cast it to void*, it works fine in all cases.

I guess for the c#9 pointer to work correctly, Burst, JobSystem, and IL2CPP all need to be modified to get the method signatures correctly.

If it is technically fixable, I would appreciate your response.

 

Code (CSharp):

1. using System.Runtime.InteropServices;
2. using AOT;
3. using Unity.Burst;
4. using Unity.Jobs;
5. using UnityEngine;
6.  
7. public unsafe class FunctionPointerC9Burst : MonoBehaviour {
8.     [UnmanagedFunctionPointer(CallingConvention.Cdecl)] private delegate int UnmanagedDelegate(int value);
9.     [MonoPInvokeCallback(typeof(UnmanagedDelegate))] private static int Increment(int value) => ++value;
10.     private static readonly delegate* unmanaged[Cdecl]<int, int> c9Ptr
11.         = (delegate* unmanaged[Cdecl]<int, int>) Marshal.GetFunctionPointerForDelegate((UnmanagedDelegate) Increment);
12.  
13.     private void Start() {
14.         var job = new Job() {fp = c9Ptr, Value = 0};
15.         job.Run();
16.     }
17. }
18.  
19. [BurstCompile]
20. public unsafe struct Job : IJob {
21.     public delegate* unmanaged[Cdecl]<int, int> fp;
22.     public int Value;
23.     public void Execute() => Debug.Log($"Value: {fp(Value)}");
24. }

Thanks for your reply. As for JobSystem, I can reproduce the above error with one file. 2022.3.4f1 (LTS)

 

Code (CSharp):

1. using System.Runtime.InteropServices;
2. using AOT;
3. using Unity.Burst;
4. using UnityEngine;
5.  
6. [BurstCompile] public unsafe class FunctionPointerC9Burst : MonoBehaviour {
7.     [UnmanagedFunctionPointer(CallingConvention.Cdecl)] private delegate int UnmanagedDelegate(int value);
8.     [MonoPInvokeCallback(typeof(UnmanagedDelegate))] private static int Increment(int value) => ++value;
9.     private static readonly delegate* unmanaged[Cdecl]<int, int> c9Ptr
10.         = (delegate* unmanaged[Cdecl]<int, int>) Marshal.GetFunctionPointerForDelegate((UnmanagedDelegate) Increment);
11.     private void Start() => IL2CppError(c9Ptr, 0);
12.  
13.     [BurstCompile] private static void IL2CppError(delegate* unmanaged[Cdecl]<int, int> unmanagedCallback, int value)
14.         => Debug.Log($"Call C#9 Function Pointer: {unmanagedCallback(value)}");
15. }

This is an error in the Android build of IL2CPP. (2022.3.4f1) This is also reproducible with one file above.

 

Thanks for the reply. Good to hear that there is a walk-around. Here is the bug report number.

IN-48119 - IL2CPP Build ErrorWhen Method First Parameter Is Unmanaged Delegate

Edit:
Unity Issue Tracker - [Android] IL2CPP build error occurs when method first parameter is an unmanaged delegate (unity3d.com)