What's new in .NET 6 Preview 3

[leecow]

What's new in .NET 6 Preview 3

This issue is for teams to highlight work for the community that will release .NET 6 Preview 3.

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

[benaadams]

.NET Libraries: System.Runtime.InteropServices - CollectionsMarshal.GetValueRef

dotnet/runtime#49388

Updating struct values in dictionaries currently can be expensive as it requires a dictionary lookup and a copy to stack of the struct; then after changing the struct it needs to be assigned to the dictionary key again resulting in another look up and copy operation.

A new unsafe api has been added; for high preformance scenarios, that returns a ref to the struct value which can then be updated in place. This reduces the key hashing to 1 (from 2) and removes all the struct copy operations.

Example:

ref MyStruct value = CollectionsMarshal.GetValueRef(dictionary, key);
// Returns Unsafe.NullRef<TValue>() if it doesn't exist; check using Unsafe.IsNullRef(ref value)
if (!Unsafe.IsNullRef(ref value))
{
    // Mutate in-place
    value.MyInt++;
}

[benaadams]

Faster interface checking and casting

dotnet/runtime#49257

One of the advantages of more parts of the .NET VM moving from C++ to managed C# is its easier to contribute to,
this includes interface casting.

.NET 6 Preview 3 includes a 16% - 38% performance boost for interface casting; this is particularly useful for C#'s pattern matching to and between interfaces.

Method	Implementation	Mean	Version	Ratio	Improvement
IsInterface1	Interfaces1	2.166 ns	.NET 6 Preview 2	1.000
IsInterface1	Interfaces1	1.629 ns	.NET 6 Preview 3	0.752	x1.3
IsNotImplemented	Interfaces1	2.166 ns	.NET 6 Preview 2	1.000
IsNotImplemented	Interfaces1	1.950 ns	.NET 6 Preview 3	0.900	x1.1
IsInterface1	Interfaces6	2.155 ns	.NET 6 Preview 2	1.000
IsInterface1	Interfaces6	1.936 ns	.NET 6 Preview 3	0.898	x1.1
IsInterface2	Interfaces6	2.161 ns	.NET 6 Preview 2	1.000
IsInterface2	Interfaces6	1.908 ns	.NET 6 Preview 3	0.883	x1.1
IsInterface3	Interfaces6	2.188 ns	.NET 6 Preview 2	1.000
IsInterface3	Interfaces6	1.672 ns	.NET 6 Preview 3	0.764	x1.3
IsInterface4	Interfaces6	2.346 ns	.NET 6 Preview 2	1.000
IsInterface4	Interfaces6	1.965 ns	.NET 6 Preview 3	0.838	x1.2
IsInterface5	Interfaces6	3.122 ns	.NET 6 Preview 2	1.000
IsInterface5	Interfaces6	2.173 ns	.NET 6 Preview 3	0.696	x1.4
IsInterface6	Interfaces6	3.472 ns	.NET 6 Preview 2	1.000
IsInterface6	Interfaces6	2.687 ns	.NET 6 Preview 3	0.774	x1.3
IsNotImplemented	Interfaces6	3.644 ns	.NET 6 Preview 2	1.000
IsNotImplemented	Interfaces6	3.071 ns	.NET 6 Preview 3	0.843	x1.2

[danmoseley]

Thanks for adding these @benaadams !

[JulieLeeMSFT]

CodeGen

Community contributions

• @nathan-moore Remove bounds checks with tests against length Jit: Remove bounds checks with tests against length. runtime#40180
• @SingleAccretion Span bounds check elision with top-level range check nodes removal Remove top-level range check nodes runtime#49271

Dynamic PGO dotnet/runtime#43618

• JIT: profile updates for return merges and tail calls JIT: profile updates for return merges and tail calls runtime#48773
• Class profile: Use unknown placeholder for collectible class typehandle Use unknown placeholder for collectible class typehandle runtime#48707

Stabilize performance measurements dotnet/runtime#43227

• Blog post on Loop Alignment https://devblogs.microsoft.com/dotnet/loop-alignment-in-net-6/

Keep structs in register dotnet/runtime#43867

• Completed struct improvement, part1: create more LCL_FLD struct improvement, part1: create more LCL_FLD runtime#48377
• Improve liveness for 'STORE_BLK(lcl_var)' Improve liveness for 'STORE_BLK(lcl_var)'. runtime#48797

Completed .NET 6 EH Write Thru dotnet/runtime#35923

• Enregister EH var that are single def Enregister EH var that are single def runtime#47307
• 7 ~ 18% perf improvement [Perf] Changes at 3/10/2021 12:58:37 AM DrewScoggins/performance-2#4275 (comment)

Optimizations:

• Support loop cloning of byte array accesses Support loop cloning of byte array accesses runtime#48894
• JIT: Non-void ThrowHelpers JIT: Non-void ThrowHelpers runtime#48589
• CSE for floating-point constants Enable CSE for floating-point constants runtime#44419
• Invariant static readonly fields to enable CSE/Hoist-from-loops optimizations [RyuJIT] static readonly fields can be Invariant runtime#44562
• Fold more with null checks for const string JIT: Fold null checks for const strings runtime#49930
• Zero init elimination: Don’t init tracked temps without GC fields Don't init tracked temps without GC fields. runtime#49879

[davidortinau]

.NET MAUI

Community Contributions

• Switch Entry and Editor from EditText to AppCompatEditText
• maui-check dotnet CLI tool

• Port font to Editor
• Implement IsTextPredictionEnabled property on Editor
• Implemented LineHeight on Label
• Entry ClearButtonVisibility handler
• Implement CharacterSpacing property in Entry handler
• Port Editor Placeholder text and color properties

Windows Platform Added

dotnet/maui#548

// images coming

With the release of Project Reunion 0.5, .NET MAUI now supports Windows development on .NET 6 Preview 3. Using Visual Studio 16.10 latest public preview, clone the .NET 6 sample here for your first look at .NET MAUI with WinUI 3. When .NET build tooling support is enabled for Project Reunion, we will add Windows to the project template and enable single project features.

Platform Lifecycle Events

A new extension has been added to enable application and library authors to easily hook-in to any native lifecycle event. A basic example is connecting to the Android back button event:

public class Startup : IStartup
{
    public void Configure(IAppHostBuilder appBuilder)
    {
        appBuilder
            .UseMauiApp<App>()
            .ConfigureLifecycleEvents(lifecycle => {
                #if ANDROID
                lifecycle.AddAndroid(d => {
                    d.OnBackPressed(activity => {
                        System.Diagnostics.Debug.WriteLine("Back button pressed!");
                    });
                });
                #endif
            });
    }
}

I'm writing a deep dive blog that will go into much more detail

Incremental Updates

// control gallery image coming

• Continued porting of UI controls and properties from Xamarin.Forms renderers to .NET MAUI handlers:
  o ActivityIndicator
  o Button
  o CheckBox
  o DatePicker
  o Editor
  o Entry
  o Label
  o Picker
  o ProgressBar
  o SearchBar
  o Slider
  o Stepper
  o Switch
  o TimePicker
• Expanded font support across handlers
• Grid added support for absolute and auto-sizing
• Implemented LayoutAlignment for all layouts
• Application updates for
  • simplified HostBuilder integration
  • new RegisterFormsCompatibility() method enables using App.xaml and auto-registers compatibility renderers
  • added loading global ResourceDictionary

Changes from Preview 2

• MauiApp is replaced with Application
• SharedImage and SharedFont are changed to MauiImage and MauiFont

[sps014]

@leecow Since Dotnet 6 preview 3 is already released this issue can be closed.

[mairaw]

Preview 3 was released: https://devblogs.microsoft.com/dotnet/announcing-net-6-preview-3/