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.NET Core Common Language Runtime (CoreCLR)
===========================

This repository contains complete source code the runtime of [.NET Core](http://dotnet.github.io).
If you are new to .NET Core start with the [About .NET](https://docs.microsoft.com/en-us/dotnet/articles/about/) 
that quickly points you to [.NET Core Tutorials](https://docs.microsoft.com/en-us/dotnet/articles/core/getting-started)


.NET Core is best thought of as 'agile .NET'.   Generally speaking it is the same as 
the [Desktop .NET Framework](https://en.wikipedia.org/wiki/.NET_Framework)
distributed as part of the Windows operating system, but it is a cross platform 
(Windows, Linux, macOS) and cross architecture (x86, x64, arm) subset that can be deployed
as part of the application (if desired), and thus can be updated quickly to fix bugs or add features.  

## If You Just Want to Use .NET Core

Most users don't need to build .NET Core from source since there is already an built and tested version for any supported platform.
You can get the latest **released** version of the .NET Core SDK by following the instructions on 
the [.NET Core Getting Started](http://dotnet.github.io/getting-started/) page.
If you need the most up to date (daily) version of this .NET Core installer you can get it from the
[latest Installers of .NET Core and .NET Core SDK](https://github.com/dotnet/cli#installers-and-binaries).

## Are you Here for Something Besides the Source Code?  

In addition to providing the source code, this repository also acts as a useful nexus for things
related to .NET Core including:

 * Want to **learn more** about .NET Runtime Internals?  See the [Documentation on the .NET Core Runtime](Documentation/README.md) page.
 * Need to **log a issue** or Provide Feedback?   See then [Issues and Feedback Page](Documentation/workflow/IssuesFeedbackEngagement.md) page.
 * Want to **chat** with other members of the CoreCLR community?  See the [Chat Section](Documentation/workflow/IssuesFeedbackEngagement.md#Chat-with-the-CoreCLR-community) page.
 * Need a **current build** or **test results** of the CoreCLR repository?   See the [Official and Daily Builds](Documentation/workflow/OfficalAndDailyBuilds.md) page.
 * If you want powerful search of the source code for both CoreClr and CoreFx see [.NET Source Code Index](https://source.dot.net)

## What Can you Make from this Repository?

.NET Core relies heavily on the [Nuget](https://en.wikipedia.org/wiki/NuGet) package manager,
which is a system to package, distribute and version software components.  See [https://www.nuget.org/](https://www.nuget.org/) 
for more information on Nuget.   For now it is enough to know Nuget is a system that
bundles components into `*.nupkg` files (which are ZIP archives) and these packages can be 'published' 
either through a local file system path or by a URL (e.g. https://www.nuget.org/).   There are then tools 
(e.g. Nuget.exe, Visual Studio, dotnet.exe) that based on a configuration file (.csproj) know 
how to search these publishing locations and pull down consistent set of packages for the 
application.   

In concrete terms, this repository is best thought of as the source code for the following Nuget package
 
 * **Microsoft.NETCore.Runtime.CoreCLR** - Represents the object allocator, garbage collector (GC), class 
   loader, type system, interop and the most fundamental parts of the .NET class library (e.g. 
   System.Object, System.String ...) 

It also contains the source code for the following closely related support packages. 

 * **Microsoft.NETCore.Jit** - The Just In Time (JIT) compiler for the 
   [.NET Intermediate language (IL)](https://en.wikipedia.org/wiki/Common_Intermediate_Language)
 * **Microsoft.NETCore.ILAsm** - An assembler for the 
   [.NET Intermediate language (IL)](https://en.wikipedia.org/wiki/Common_Intermediate_Language)
 * **Microsoft.NETCore.ILDAsm** - A disassembler (Pretty printer) for the
   [.NET Intermediate language (IL)](https://en.wikipedia.org/wiki/Common_Intermediate_Language)
 * **Microsoft.NETCore.TestHost** - This contains the corehost.exe program, which is a small wrapper 
   that uses the .NET Runtime to run IL DLLs passed to it on the command line.
 * **Microsoft.TargetingPack.Private.CoreCLR** - A set of assemblies that represent the compile time surface 
   area of the class library implemented by the runtime itself.

## Relationship with the [CoreFX](https://github.com/dotnet/corefx) Repository 

By itself, the `Microsoft.NETCore.Runtime.CoreCLR` package is actually not enough to do much.
One reason for this is that the CoreCLR package tries to minimize the amount of the class library that it implements.
Only types that have a strong dependency on the internal workings of the runtime are included (e.g, 
`System.Object`, `System.String`, `System.Thread`, `System.Threading.Tasks.Task` and most foundational interfaces).
Instead most of the class library is implemented as independent Nuget packages that simply use the .NET Core 
runtime as a dependency.    Many of the most familiar classes (`System.Collections`, `System.IO`, `System.Xml` and 
so on), live in packages defined in the [dotnet/corefx](https://github.com/dotnet/corefx) repository.

But the main reason you can't do much with CoreCLR is that **ALL** of the types in the class library **LOOK** 
like they are defined by the CoreFX framework and not CoreCLR.   Any library code defined here 
lives in a single DLL called `System.Private.CoreLib.dll` and as its name suggests is private (hidden).
Instead for any particular PUBLIC type defined in CoreCLR, we found the 'right' package in CoreFX where it naturally 
belongs and use that package as its **public publishing** point.   That 'facade' package then forwards references 
to the (private) implementation in `System.Private.CoreLib.dll` defined here.
For example the *`System.Runtime`* package defined in CoreFX declares the PUBLIC name for types like 
`System.Object` and `System.String`.   Thus from an applications point of view these types live in `System.Runtime.dll`. 
However, `System.Runtime.dll` (defined in the CoreFX repo) forwards references ultimately to `System.Private.CoreLib.dll` 
which is defined here.

Thus in order to run an application, you need BOTH the `Microsoft.NETCore.Runtime.CoreCLR` Nuget package 
(defined in this repository) as well as  packages for whatever you actually reference that were defined 
in the CoreFX repository (which at a minimum includes the `System.Runtime` package).    You also need some 
sort of 'host' executable that loads the CoreCLR package as well as the CoreFX packages and starts your code (typically 
you use `dotnet.exe` for this).   

These extra pieces are not defined here, however you don't need to build them in order to use the CoreCLR 
Nuget package you create here.   There are already versions of the CoreFX packages published on 
https://www.nuget.org/ so you can have your test application's project.json specify the CoreCLR you 
built and it will naturally pull anything else it needs from the official location https://www.nuget.org/ to 
make a complete application.  More on this in the [Using Your Build](Documentation/workflow/UsingYourBuild.md) page.

--------------------------
## Setting up your GIT Clone of the CoreCLR Repository

The first step in making a build of the CoreCLR Repository is to clone it locally.   If you already know
how to do this, just skip this section.  Otherwise if you are developing on windows you can see
[Setting Up A Git Repository In Visual Studio 2015](https://github.com/Microsoft/perfview/blob/master/documentation/SettingUpRepoInVS2015.md)
for for instructions on setting up.  This link uses a different repository as an example, but the issues (do you fork or not) and
the procedure are equally applicable to this repository.  

--------------------------
## Building the Repository

The build depends on Git, CMake, Python and of course a C++ compiler.  Once these prerequisites are installed
the build is simply a matter of invoking the 'build' script (`build.cmd` or `build.sh`) at the base of the 
repository.  

The details of installing the components differ depending on the operating system.  See the following
pages based on your OS.  There is no cross-building across OS (only for ARM, which is built on X64).  
You have to be on the particular platform to build that platform.  

 * [Windows Build Instructions](Documentation/building/windows-instructions.md)
 * [Linux Build Instructions](Documentation/building/linux-instructions.md)
 * [macOS Build Instructions](Documentation/building/osx-instructions.md)
 * [FreeBSD Build Instructions](Documentation/building/freebsd-instructions.md) 
 * [NetBSD Build Instructions](Documentation/building/netbsd-instructions.md)

The build has two main 'buildTypes'

 * Debug (default)- This compiles the runtime with additional runtime checks (asserts).  These checks slow 
   runtime execution but are really valuable for debugging, and is recommended for normal development and testing.  
 * Release - This compiles without any development time runtime checks.  This is what end users will use but 
   can be difficult to debug.   Passing 'release' to the build script select this.  

In addition, by default the build will not only create the runtime executables, but it will also 
build all the tests.   There are quite a few tests so this does take a significant amount of time
that is not necessary if you want to experiment with changes.   You can submit the building
of the tests with the 'skiptests' argument to the build script.

Thus to get a build as quickly as possible type the following (using `\` as the directory separator, use `/` on Unix machines)
```bat
    .\build skiptests 
```
which will build the Debug flavor which has development time checks (asserts), or 
```bat 
    .\build release skiptests
```
to build the release (full speed) flavor.  You can find more build options with build by using the -? or -help qualifier.   

## Using Your Build

The build places all of its generated files under the `bin` directory at the base of the repository.   There 
is a `bin\Log` directory that contains log files generated during the build (Most useful when the build fails).
The the actual output is placed in a directory like this 

* bin\Product\Windows_NT.x64.Release

Where you can see the operating system and CPU architecture, and the build type are part of the name.   While
the 'raw' output of the build is sometimes useful, normally you are only interested in the Nuget packages 
that were built, which are placed in the directory 

* bin\Product\Windows_NT.x64.Release\.nuget\pkg

These packages are the 'output' of your build.   

There are two basic techniques for using your new runtime.

 1. **Use dotnet.exe and Nuget to compose an application**.   See [Using Your Build](Documentation/workflow/UsingYourBuild.md) for 
 instructions on creating a program that uses 
 your new runtime by using the NuGet packages you just created and the'dotnet' command line interface.  This
 is the expected way non-runtime developers are likely to consume your new runtime.    

 2. **Use corerun.exe to run an application using unpackaged Dlls**. This repository also defines a simple host called
 corerun.exe that does NOT take any dependency on NuGet.   Basically it has to be told where to get all the
 necessary DLLs you actually use, and you have to gather them together 'by hand'.   This is the technique that
 all the tests in the repo use, and is useful for quick local 'edit-compile-debug' loop (e.g. preliminary unit testsing).
 See [Executing .NET Core Apps with CoreRun.exe](Documentation/workflow/UsingCoreRun.md) for details on using 
 this technique.  

## Editing and Debugging

Typically users run through the build and use instructions first with an unmodified build, just to familiarize
themselves with the procedures and to confirm that the instructions work.   After that you will want to actually
make modifications and debug any issues those modifications might cause.   See the following links for more.   

 * [Editing and Debugging](Documentation/workflow/EditingAndDebugging.md) and
 * [Documentation on the .NET Core Runtime](Documentation/README.md)

## Running Tests 

After you have your modification basically working, and want to determine if you have broken anything it is 
time to runt tests.  See [Running .NET Core Tests](Documentation/workflow/RunningTests.md) for more. 

## Contributing to Repository 

Looking for something to work on? The list 
of [up-for-grabs issues](https://github.com/dotnet/coreclr/labels/up-for-grabs) is a great place to start.

Please read the following documents to get started.

* [Contributing Guide](Documentation/project-docs/contributing.md)
* [Developer Guide](Documentation/project-docs/developer-guide.md)

This project has adopted the code of conduct defined by the [Contributor Covenant](http://contributor-covenant.org/) 
to clarify expected behavior in our community. For more information, see the [.NET Foundation Code of Conduct](http://www.dotnetfoundation.org/code-of-conduct).

-------------------
## Related Projects

As noted above, the CoreCLR Repository does not contain all the source code that makes up the .NET Core distribution.
Here is a list of the other repositories that complete the picture.  

* [dotnet/corefx](https://github.com/dotnet/corefx) - Source for the most common classes in the .NET Framework library.
* [dotnet/core-setup](https://github.com/dotnet/core-setup) - Source code for the dotnet.exe program and the policy logic
to launch basic .NET Core code (hostfxr, hostpolicy) which allow you to say 'dotnet SOME_CORE_CLR_DLL' to run the app.  
* [dotnet/cli repo](https://github.com/dotnet/cli) - Source for build time actions supported by dotnet.exe Command line Interface (CLI).
Thus this is the code that runs when you do 'dotnet build', 'dotnet restore' or 'dotnet publish'.
* [dotnet/core-docs](https://github.com/dotnet/core-docs) - Master copy of documentation for 
[http://docs.microsoft.com/en-us/dotnet/](https://docs.microsoft.com/en-us/dotnet/)

## See Also

* [Dotnet.github.io](http://dotnet.github.io) is a good place to discover .NET Foundation projects.
* .NET Core is a [.NET Foundation](http://www.dotnetfoundation.org/projects) project.
* [.NET home repo](https://github.com/Microsoft/dotnet) links to 100s of .NET projects, from Microsoft and the community.
* The [.NET Core repo](https://github.com/dotnet/core) links to .NET Core related projects from Microsoft.
* The [ASP.NET home repo](https://github.com/aspnet/home) is the best place to start learning about ASP.NET Core.

## Important Blog Entries

* [Announcement of .NET Core Open Source Project](http://blogs.msdn.com/b/dotnet/archive/2014/11/12/net-core-is-open-source.aspx)
* [Introducing .NET Core](http://blogs.msdn.com/b/dotnet/archive/2014/12/04/introducing-net-core.aspx)
* [Announcement of CoreCLR](http://blogs.msdn.com/b/dotnet/archive/2015/02/03/coreclr-is-now-open-source.aspx)

## License

.NET Core (including the coreclr repo) is licensed under the [MIT license](LICENSE.TXT).

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