Open Source .NET technology explained Atsushi Eno (atsushieno/@atsushi_eno) goo.gl/0hxxIT 

/me ● Mono project developer, .NET Core contributor ● Software engineer at Xamarin ● lurking around H4 and TOSSUG (when in Taipei) 

my COSCUP sessions on OSS & .NET ● 2013: MonoDevelop IDE ○ how the IDE works. ● 2014: Mono and Open Source .NET ○ how Mono is made up with OSS-ed .NET parts ● 2015: .NET Core ○ what .NET Core is, how it works. (meh, the topics are getting bloat...) 

Agenda ● The situation how .NET Core was born ● See how .NET Core works ● Current .NET Core status and visions 

Quick intro to .NET Framework ● A complete development platform (like Java) ○ ECMA 335 (CLI) high-level VM, statically-typed system (similar to jvm) foundation class libraries (similar to rt.jar) beyond standards: DB, Web, GUI... well-thought assembly (library) versioning support ○ ECMA 334 (C#) statically-typed compilers (similar to java) 

what is .NET dev. experience like? ● mostly awesome ○ solid and mature framework libraries ○ C# is stable yet evolving ○ the IDE (Visual Studio) experience is supreme 

is .NET perfect then? ● NO! NO! NO! ○ it's not quite handy, need to install .NET Fx ○ apps easily become Windows-only ○ too much of Windows-isms ○ too many framwork variants, hard to support all ○ .NET Fx development is getting slow ○ updatable only in sync with Windows or VS releases. ○ several issues due to closed source 

Wait, I heard that .NET is cross platform... Yes we are cross platform! 

There is Mono, it is truly x-plat Mono complements .NET defects ● cross platform ● open source ● non-Windows native API Also, Microsoft friendly Problems ● not (meant to be) fully compatible w/ .NET Fx ● not actively developing server stack anymore ● Xamarin went mobiles, leaving Linux desktop 

x-plat ain't easy ● SL, WP, StoreApp, Xamarin ... different Fx and versions ○ because everything cannot be implemented everywhere ○ You cannot reference Desktop assemblies in those frameworks ○ Normally libraries need to be built for those platforms ● PCL (Portable Class Library) makes it easy ○ you build your library as a PCL project ○ PCLs can be referenced by any (of the profile targets) ○ For PCLs, you specify Profile, not dll references ○ packages via NuGet.org (zip archive of dlls, resources and tools) 

How is PCL support implemented? (briefly) ● modularized core libraries ○ so each Profile is represented as a set of feature assemblies ● Type forwarding ○ PCL "Facade" assemblies don't have implementation ○ instead, they have [TypeForwardedTo] attributes. 

ASP.NET evolution ● Web Forms o very easy (even for VB coders) x integration with external JavaScript was horrible ASP.NET Ajax ● MVC o that's what normal Web dev. wanted. o started as an OSS project, and extended OSS-ism. x depends on System.Web 

What's wrong with System.Web? ● part of .NET Fx - hard to upgrade ● Web dev. trends need low-level support ○ non-blocking I/O (libuv) ○ HTTP/2 ● needs updatable lightweight deployment framework 

● "Introducing .NET Core" (.NET team blog) ● portable subset of .NET Fx ● sort out all of those known issues ○ MIT license w/ patent covenant ○ standalone redist-able, per app ○ x-plat ● release stages: src(git)/pkg/Fx the rise of .NET Core 

.NET Core components (briefly) ● coreclr - runtime (VM) ● roslyn - C# compiler ● corefx - foundation class libraries ● aspnet - web app framework 

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Running .NET Core ● Use "DNX SDK" (dnvm) ○ installer https://github.com/dotnet/coreclr#get-net-core or Docker ○ ... or manually set up everything (complicated) ● app files: (C#) sources, package.json (project config) ● Run ○ set up dnvm (dnvm: runtime configurator; see coreclr docs) like update-alternatives ○ dnu restore (dnu: package resolver) ○ dnx (-p) . run (dnx: runtime, -p is very new option) ○ dnvm install 1.0.0-beta7-12275 -r coreclr -u; dnvm install 1.0.0-beta7-12275 -u; dnu restore; dnvm use 1.0.0-beta7-12275 -r coreclr; dnx . run 

Running .NET Core ● How things work ○ dnvm (framework/selector) ■ the Fx runtime backend can be: clr, mono, coreclr ○ dnu (package resolver) ■ based on nuget ○ dnx (runtime) ■ uses roslyn (compiler) to compile app at run time 

Building .NET Core (Well, you can build them, but managing everything to run app is messy.) ● coreclr runtime ○ you need Windows to build mscorlib.dll ○ or, some people offer precompiled ones ○ or, use my patched build that partially works (PR1275) ● corefx classlibs ○ builds on Linux/Mac/Win (often fails outside Windows) ○ still lacks PCL Facades - need to download binaries (dnu restore) ● roslyn compiler ○ Windows for full build, or partial x-plat build 

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coreclr ● .NET Core runtime (VM) ○ Rotor (SSCLI) -> Silverlight (on Mac) -> this ○ EE (execution engine) , GC, native interop, JIT, debugging ○ mscorlib.dll (as it is tightly-coupled with the VM) ○ architecture docs for hackers: Book of the Runtime (BotR), CoreCLR Coding Guide (in the github repo) but you would be just happy with existing .NET readings, they are so advanced... 

corefx ● managed class libraries ● subset of .NET FCL ○ StoreApp/Silverlight/Phone, excluding UI, Plat-specific ○ Not fully done, see corefx-progress repo 

roslyn ● compiler infrastructure: compilers + "services" ○ => my COSCUP2013 slides ○ Used by VS2015, MonoDevelop6 and "omnisharp" ● managed C#/VB compiler implementation ○ easy to extend by .NET devs ● debug symbols are getting portable (PPDB - very new) 

aspnet ● The revamped ASP.NET. ○ decomposed System.Web into many packages ○ cross platform from scratch. ■ app runtime: dnx (so, clr/mono/coreclr) ■ server: IIS (Helios), libuv (Kestrel), self-host (WebListener) ○ own packaging / dependency system: dnu ■ Hosting, Mvc, SignalR, Identity, EntityFramework, ... ○ dynamic compilation using Roslyn (as dnx does) 

related: referencesource ● incomplete sources for .NET Framework (not .NET Core) ● It is mostly for Mono project ○ so that Mono can import it, for improved compatiblity. ○ Mono is importing them, but cannot simply replace. ■ remove Windows-isms, mobile restrictions etc. 

related: msbuild ● MSBuild is needed to build .NET Core themselves. ● Needed for cross platform build. ○ Mono implementation (xbuild) is old and incomplete. ● getting x-plat ready now. 

related: llilc ● Another JIT implementation for coreclr ○ JIT = native executable code generator ○ coreclr JIT is pluggable (can be replaced) ● JIT implementation trend: use LLVM native codegen ○ to support as many platforms as LLVM supports. ● llilc: coreclr JIT implementation using LLVM ● under development yet 

related: Visual Studio Code ● NOT open source (yet?) ● Cross platform IDE for .NET Core ● Very simple IDE. Just an enhanced code editor + debugger ○ But what is an "IDE" ? >> my COSCUP2013 slides ● built upon Electron (Atom Shell) ● supports C# and TypeScript (TS has language service) 

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the state of .NET Core ● .NET Core: the future .NET platform (i.e. not now) ○ .NET Framework etc. will be based on it. ● code status ○ coreclr - Windows dependencies in the build system ○ corefx - more porting work needed ○ no integrated build/installs. ○ builds are not stable yet. Builds on CI servers are almost fake. ● ASP.NET - on its own roadmap 

the state of Mono ● is Mono still needed? ○ cross platform is still big TODO at .NET Core. ○ There is mono ecosystem (Gtk# and apps) ○ so as Xamarin platforms ● Mono visions ○ import more referencesource for .NET compatibility ○ reuse good coreclr parts (e.g. GC) 

How can you benefit from .NET Core? ● For now if you just write apps, use .NET Framework etc. ! ● You can understand the underlying Fx you use better. ● You can build and ship app with your own .NET Core build. ○ ship with fixed version of .NET Core ○ modify the Fx behavior to fit your app's need. ● You can research how the modern dev. framework works. 

.NET Core: Possible use cases ● Learn from what Mono has done in the past ● Hosting CoreCLR ○ Office.NET, CLI-UNO (LibreOffice) ○ SQLCLR ○ Unity3D etc. ● Develop another .NET based framework? ○ Browser plugin? (Silverlight/Moonlight => WebAssembly) ○ IoT? (.NET Micro Framework) ○ new mobile platforms? (Xamarin) 

developing (contributing to) .NET Core ● .NET Core hosted at github. They accept PRs. ○ Cup ● still not easy to try integration tests with private hacks... 

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Summary 

Lastly... Anyone interested in .NET Core dev group? Let me know 

Thanks