What's new in .NET 6 Preview 1

[leecow]

What's new in .NET 6 Preview 1

This issue is for teams to highlight work for the community that will release .NET 6 Preview 1.

To add content, use a new conversation entry. The entry should include the team name and feature title as the first line as shown in the template below.

## Team Name: Feature title

[link to the tracking issue or epic item for the work]

Tell the story of the feature and anything the community should pay particular attention 
to be successful using the feature.

Preview 1: #5853
Preview 2: #5889
Preview 3: #5890
Preview 4: #6098
Preview 5: #6099
Preview 6: #6325
Preview 7: #6444
RC1: #6569
RC2: #6570

[tannergooding]

.NET Libraries: System.Numerics - New math APIs

New math APIs which may be hardware accelerated if the underlying hardware supports it:

• SinCos for simultaneously computing Sin and Cos
• ReciprocalEstimate for computing an approximate of 1 / x
• ReciprocalSqrtEstimate for computing an approximate of 1 / Sqrt(x)

New math API overloads:

• Clamp, DivRem, Min, and Max supporting nint and nuint
• Abs and Sign supporting nint
• DivRem variants which return a tuple

[carlossanlop]

.NET Libraries: System.Threading.AccessControl - Ported Windows ACL APIs

New overloads were added to the OpenExisting and TryOpenExisting methods for EventWaitHandle, Mutex and Semaphore. By accepting "security rights" instances, the overloads enable users to open existing instances of threading synchronization objects that were created with special Windows security attributes.

These APIs are Windows-specific and available via the System.Threading.AccessControl assembly; they were ported from .NET Framework:

namespace System.Threading
{
    public static partial class EventWaitHandleAcl
    {
        public static EventWaitHandle OpenExisting(string name, EventWaitHandleRights rights);
        public static bool TryOpenExisting(string name, EventWaitHandleRights rights, out EventWaitHandle result);
    }
    public static partial class MutexAcl
    {
        public static Mutex OpenExisting(string name, MutexRights rights);
        public static bool TryOpenExisting(string name, MutexRights rights, out Mutex result);
    }
    public static partial class SemaphoreAcl
    {
        public static Semaphore OpenExisting(string name, SemaphoreRights rights);
        public static bool TryOpenExisting(string name, SemaphoreRights rights, out Semaphore result);
    }
}

[JamesNK]

ASP.NET Core: appsettings.json autocomplete

appsettings.json now has autocomplete in Visual Studio and VSCode (with C# extension).

The JSON schema for appsettings.json was updated to include commonly used configuration in ASP.NET Core, including configuring logging, host filtering and Kestrel.

[JulieLeeMSFT]

CodeGen

Dynamic PGO dotnet/runtime#43618

• Enable guarded devirtualization by class profile and probes for class types Initial version of class profiling for PGO runtime#45133
• Graphical dump of flow graph with profile data JIT: show profile data for dot flowgraph dumps runtime#42657
• Redundant branch elimination JIT: jump threading runtime#46257
• Enable CSE of PGO introduced type tests JIT: consistently mark method table accesses as invariant runtime#45854

ABI changes for Apple Silicon dotnet/runtime#41130

• Stack arguments passing in managed <-> native calls:
  Jit preparation for arm64 apple: Use bytes in fgArgTabEntry. runtime#42503
  arm64 osx: support byte sizes from lowering to codegen. runtime#43024
  Keep precise argument sizes between import and morph. runtime#43130
  Fix arm64 apple hfa<float>. runtime#46034
  VM fixes for delegate/reflection Arm64 apple vm fixes for arg alignment. runtime#46665

Advanced Arm64 support dotnet/runtime#43629

• Stack frame zeroing using stp and str SIMD [Arm64] Use SIMD register to zero init frame runtime#46609

Stabilize performance measurements dotnet/runtime#43227

• Inner loop alignment Align inner loops runtime#44370

Keep structs in register dotnet/runtime#43867

• Struct promotion for HFA and non-HFA multireg args on x64 and Arm64 Handle additional multireg args runtime#43870
• Enregister HFAs and other structs with matching fields Allow enregistering more structs args runtime#39326

[agocke]

AppModel

"Superhost" for Windows and Mac: dotnet/runtime#43072

In 5.0 we debuted the "superhost" for Linux, which linked all the CoreCLR native binaries into a single host, and embedded all libraries inside the same file, avoiding any file extraction.

In 6.0 we're continuing this work by brining the superhost to Windows and Mac, meaning users can now publish a single-file binary that has exactly one file on disk and does not need to extract any of the core runtime assemblies to temporary directories.

Facilitate single-file signing on MacOS: dotnet/runtime#3671

Signing/notarization on MacOS has very strict requirements for the layout of binaries. This change fixes single-file to conform to those requirements, allowing single-file apps to be notarized and signed.

[sdmaclea]

.NET CoreCLR Runtime: Support Apple Silicon dotnet/runtime#43313

.NET Rosetta 2 Emulation dotnet/runtime#44897

Apple release of Big Sur 11.2 Beta 2 has resolved most issue running .NET 5.0 under Rosetta 2 emulation. Prior to Big Sur 11.2 Beta 2 there were significant issues with Rosetta 2 emulation, upgrade of M1's to to Big Sur 11.2 is strongly recommended.

• .NET 5.0 testing by Apple, Microsoft, and Community shows:

  • Debugger is fully functional
  • Stability issues are resolved
  • Slowness when running with debugger

• .NET 6.0 preview1 and .NET Core 3.1 have not yet been tested by Microsoft under Rosetta 2, but are expected to work similarly to .NET 5.0. Community has not reported any particular issues with .NET Core 3.1.

• The recent Big Sur 11.2 release has not yet been tested (by Microsoft), but is expected to have all the updates included in 11.2 Beta 2.

.NET 6 - CoreCLR Native dotnet/runtime#43313

Native support for Apple Silicon is mostly complete in .NET 6.0 Preview 1. Native arm64 packages are now available

Known issues:

• Debugger support is completely missing. Visual Studio & VS Code debuggers will not work locally or remotely when debuggng a native Apple Silicon .NET 6 Preview 1 runtime.
• For large stack allocations, JIT can fail to generate stack clear code since M1 pagesize is 16K arm64 skippage6.sh test fails to JIT code when page size > 4KB runtime#42023.
• Runtime needs stability work
  • A small number of tests are failing GC Stress testing
  • A small number of tests exhibit intermittent failures
• CI testing is not enabled so test coverage is purely from occasional manual testing

Workarounds:

To work around the lack of debugger support, it is recommended to either:

• Debug on any other platform
• Debug the x64 under Rosetta 2 emulation
• For advanced users, use the lldb native debugger with the sos-debugging-extension. Build it from scratch from the https://github.com/dotnet/diagnostics repo. The plugin can be loaded into lldb like this:

(lldb) plugin load /Users/stmaclea/git/diagnostics/artifacts/bin/OSX.arm64.Debug/libsosplugin.dylib

[marcpopMSFT]

SDK: .NET CLI adopting the System.CommandLine libraries

Adopting System.CommandLine lights up three features in the .NET CLI

• Response files so you can save your command line arguments in a file or update them dynamically
  dotnet build @demo.rsp
  
• The suggest directive will enable you to search for commands if you don't know the exact command. This directive exists to enable the dotnet-suggest global tool

dotnet [suggest] buil
build
build-server
msbuild

• The parse directive will give you details on how the CLI is parsing your command line for better debugging.

dotnet [parse] build -f net5.0
[ dotnet [ build [ -f <net5.0> ] ] ]

[mangod9]

Portable Threadpool is enabled by default.

This is a managed implementation of the runtime Threadpool. More details are included as part of this PR: dotnet/runtime#38225. We dont expect any functional or performance impact as part of this change, but if there is any issue it can be disabled using COMPlus_ThreadPool_UsePortableThreadPool=0

[mangod9]

System.Private.Corelib assembly now precompiled by crossgen2

We have started to roll broader crossgen2 based pre-compilation. In preview1 corelib is compiled using crossgen2. Going forward we expect all Framework assemblies would be compiled with it. We havent observed any performance differences, but there are a few differences with crossgen1 in terms of which methods are compiled.

The sdk still defaults to using crossgen1 however and that will be moved over in subsequent .net 6 previews.

[predavid]

Windows Presentation Framework (WPF) : ARM64 Support

WPF ARM64 support is now available in .NET 6.0 Preview 1

Build available here

Please provide your feedback here

[richlander]

.NET 6 Preview 1 was released: https://devblogs.microsoft.com/dotnet/announcing-net-6-preview-1/