Using panama with C# dll

[Maurizio Cimadamore]

I see what you mean re. two indirections and pointer passing.

When reading the Mono embedding doc, I noticed that libmono has 
something that looks useful:

https://www.mono-project.com/docs/advanced/embedding/#unmanaged-to-managed-thunks

This allows to create a function pointer out of a mono method. Then the 
pointer can be treated as a foreign call by the linker (e.g. you can 
link against that pointer).

It's a slightly less dynamic approach (and probably more efficient), in 
that it allows, in principle, to define a library which can be used to 
"lookup" Mono methods (this will create thunks), and then link against 
them (using the linker).

The biggest issue would remain to marshal/unmarhal args/returns to and 
from Mono-land. But it seems like a useful library on top of the Linker 
could be defined using these building blocks? (then of course, one could 
also define a tool which uses said library to generate all the MHs they 
need in one go, a la jextract).

Maurizio

On 19/06/2023 11:10, Christoph Läubrich wrote:
> Hi Maurizio,
>
> thanks for your input, yes I'm currently using libmono[2] to embed C# 
> runtime and this is working to the basics but is of course a bit 
> cumbersome because one has two indirection and each require some 
> inconvenient pointer passing and method callings by string names:
>
> panama > libmono
> libmono > C#
>
> but as you can inspect the assembly for classes and methods and so on, 
> there is also another approach with jni4net [4] that generates aJNI 
> interface and according to their documentation it seems they are able 
> to directly register using JNI#RegisterNatives [6].
>
> This makes me think that probably jextract could be made to work by 
> using a C# assembly as an input and generate a binding with a nice 
> java interface, there is also already IKVM [7] that is a JVM that 
> exposes mono framework inside a JVM to javacode, so if this would work 
> inside standard OpenJDK (maybe one would need a new JDK module 
> jdk.sharp for the runtime) but maybe I'm just a bit too enthusiastic :-)
>
> And as both C# and Java are not that far apart (Object,s Exceptions, 
> Reflection, Platform Independet Bytecode) it seems a good match to 
> have some deeper inter-op.
>
> [4] https://github.com/jni4net/jni4net/tree/0.8.8.0
> [5] 
> http://zamboch.blogspot.com/2009/11/how-calling-from-java-to-net-works-in.html
> [6] 
> https://docs.oracle.com/javase/6/docs/technotes/guides/jni/spec/functions.html#wp17734
> [7] https://www.mono-project.com/docs/about-mono/languages/java/
>
> Am 19.06.23 um 11:47 schrieb Maurizio Cimadamore:
>> I am not an expert on this topic (and I'd ask others to chime in 
>> and/or validate the stuff below), but I'd assume that options to call 
>> into a C# assembly are a bit limited (since a #NET assembly doesn't 
>> use classic C ABI):
>>
>> * use a compiler that understands #NET (obviously great if you work 
>> in visual studio)
>> * use COM (I have seen examples in this sense on this mailing list)
>> * use some 3rd party solution which allows to "export" symbols from 
>> C# [1]
>> * try to find a way to embed a #NET runtime in your Java application [2]
>>
>> I believe the dlls in the project you refer to are plain #NET 
>> assemblies, so I don't think a regular (e.g. non-MSVC) compiler would 
>> be able to do much with them - and that conclusion would extend to 
>> the Linker API.
>>
>> Of these approaches, the last seem promising, as your Panama 
>> application would interact not with the assembly directlty, but with 
>> a library that implements the #NET functionalities (think of it as 
>> some kind of JNI for #NET). From there, you have ways to obtain 
>> references to #NET methods, and call them [3].
>>
>> Of course, I have not tried any of this :-)
>>
>> [1] - https://github.com/3F/DllExport
>> [2] - https://www.mono-project.com/docs/advanced/embedding/
>> [3] - 
>> https://www.mono-project.com/docs/advanced/embedding/#invoking-methods-in-the-cil-universe
>>
>>
>> On 17/06/2023 13:24, Christoph Läubrich wrote:
>>> I'm wondering if anyone has already used panama with a c# DLL[2]?
>>>
>>> I especially came across this example [1] that says
>>>
>>> > The assemblies can be used to read RAW files on Windows, Linux,
>>> > and MacOS using C# or other languages that can acces a .Net assembly
>>>
>>>
>>> So I'm wondering if similar is possible using panama/java as well?
>>>
>>>
>>> [1] https://github.com/thermofisherlsms/RawFileReader
>>> [2] 
>>> https://github.com/thermofisherlsms/RawFileReader/tree/main/libs/NetStandard20