[Mono-dev] Multiplatform support with P/Invoke

[Jason Curl]

On 2016-01-01 13:17, Miguel de Icaza wrote:
> Re-reading your original question makes me wonder if you really need 
> something as heavy handed as the approach on Mono.Posix.

Specifically I will port my .NET implementation 
http://serialportstream.codeplex.com to Mono on Linux, but why stop 
there? I would further consider BSD socket networking code which is much 
more complicated (especially obtaining interface names).
>
> The challenge that Mono.Posix faces is that the structures exposed in 
> each Unix is slightly different (different location for fields, 
> different data types for fields), so Mono.Posix resorts to defining 
> its own interface, say instead of using "struct stat" and trying to 
> have one universal implementation that works across many different 
> Unix systems - it instead defines a "struct MyStat" which has well 
> known fields at well known locations with well known sizes.
>
I've experience in writing portable code with the help of Autotools on 
Solaris, FreeBSD, Linux, Cygwin and QNX, all of which have their own 
quirks as you've needed to solve with Mono.Posix.

> Then the C glue maps between those two.
>
> But in your case, it is not clear if you are trying to bind libc and 
> their structures, or trying to bind your own C library that already 
> has a stable ABI.  If you are coping with the latter, you do not need 
> a setup as tedious as the one that Mono.Posix does, you merely need to 
> ship your native library for each platform you intend to support and 
> your C# code that calls into it.

I've not started the port of my project to Unix and so have no library 
already. I will write one though, as it seems the solution that 
Mono.Posix has taken. It also appears the only /portable/ way that I can 
take without having to make assumptions about structure layouts.
>
> Miguel

I took a further look at DllMaps, and while I haven't started/tested 
yet, I believe this can simplify effort by allowing me to having one 
native lib per architecture and a single .NET class that "standardizes" 
the interfaces I need.

I'm still researching the best way. Right now, I'm planning on having a 
Cmake/Autotools project to build my library for the platform, use 
DllMaps to let the Mono runtime pick the appropriate native library when 
running if OSVersion is Unix (etc.)

Do you have time to highlight how the MapAttribute works in Mono.Posix?

Thankyou for your support,
Jason.
>
> On Thu, Dec 31, 2015 at 8:15 PM, Jason Curl <jcurlnews at arcor.de 
> <mailto:jcurlnews at arcor.de>> wrote:
>
>     Thank you Mr. Icaza.
>
>     Is there more information on what uses the MapAttribute than
>     what's in Syscall.cs? Even though it's internal and I won't use
>     it, I'd like to understand how you solve the problem of ABI
>     compatibility.
>
>     I'd like to set up a solution where copying the files from one
>     architecture to another simply works (assuming all dependencies
>     from the runtime are present), and the runtime/mylib chooses the
>     most appropriate native library (based on OSVersion and
>     Syscall.uname) for all supported platforms. Something like:
>     * MyLib.dll (assembly)
>     * MyNativeLib.Linux.x86.so <http://MyNativeLib.Linux.x86.so>
>     * MyNativeLib.Linux.x64.so <http://MyNativeLib.Linux.x64.so>
>     * MyNativeLib.FreeBSD.x86.so <http://MyNativeLib.FreeBSD.x86.so>
>     * MyNativeLib.Darwin.x86.so <http://MyNativeLib.Darwin.x86.so>
>     * MyNativeLib.Win.x86.dll (windows native)
>     * MyNativeLib.Win.x64.dll (windows native)
>     * MyNativeLib.[dll|so] (backup for local builds)
>
>     Your solution (Mono.Unix.Native) looks different, more compact,
>     but I'm not sure if/how it supports side-by-side. My solution
>     requires a lot of work, duplicate code with small changes in
>     defining the structs/DllImports with different offsets and library
>     names.
>
>     I've yet to look into the Dll mapping mechanism of Mono if that's
>     also suitable.
>
>     Thank you very much and for giving me the opportunity to use Mono.
>
>     Regards,
>     Jason.
>