CoreCLR and project Mono relationship after Microsoft open-sourced the .NET

Question

Could someone explain to me what is the current relationship between Mono and the open source/Linux portable .NET stack (CoreCLR, CoreFX, Roslyn, ASP.NET) recently made availabl

Answer 1

From a Mono contributor on reddit:

I think people have the wrong mindset about this whole Mono/CoreCLR situation. Why should one VM becoming open source and being ported to other OSs mean that another VM can't exist? It'd be like saying that there should only be one Python implementation, or one JVM. That is not a good thing. Competition is healthy.

Mono happens to have a lot of features that CoreCLR doesn't: LLVM, full AOT, NaCl, tasklets, cross-VM GC bridge, various profiler modules, etc. Mono's startup time and runtime memory footprint are also optimized for platforms/devices that CoreCLR isn't (at least presently) even targeting. OTOH, CoreCLR has a more mature GC and generally better code generation (hence the slower startup time). The two VMs are good at different things, and there is no reason both cannot exist.

It's not like we insist on keeping our own code either. We're happy to switch to CoreCLR/reference source code when there are clear benefits to doing so (less maintenance, more correct, still portable enough). We've imported tons of reference source code already, and we're also importing certain parts of the CoreCLR VM:
https://github.com/mono/mono/blob/master/mono/metadata/decimal-ms.c
https://github.com/mono/mono/blob/master/mono/metadata/threadpool-ms.c

From a .NET member on HN:

The core framework libraries (CoreFX) - https://github.com/dotnet/corefx - are used for all .NET Core scenarios, including .NET Native (UWP). This means that your code does the same thing in all of these different environments, since it's using the same underlying framework libraries. Separately, the Mono project is taking a lot of the same code, which means that the base framework for Xamarin apps are becoming more compatible with CoreFX, too. Yeahh! We hope to make this more formal in the future. We talk to @migueldeicaza about this frequently.

Basically there's a lot of code sharing happening between them and I wont be surprised if they converge in future. Now that since MS has acquired Xamarin I dont think they will be terribly interested in maintaining two runtimes.