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What's new in .NET 8 Preview 5 [WIP] #8436

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What's new in .NET 8 Preview 5 [WIP]#8436
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@leecow
leecow
opened on May 3, 2023

What's new in .NET 8 Preview 5

This issue is for teams to highlight work for the community that will release in .NET 8 Preview 5

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

Required

## 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 in using the feature.

Optional

Below are three additional items to consider. These will help the .NET 8 blog team and the community throughout the release.

  • Link to documentation.
    • Where can we send people to learn more about the feature?
  • Link to where you'd like people to provide feedback for this feature.
    • Where can people best comment on the direction of this feature?
  • Whether you would like assistance from the .NET 8 writers to craft a story for this feature.

Index of .NET 8 releases

Preview 1: #8133
Preview 2: #8134
Preview 3: #8135
Preview 4: #8234
Preview 5: #8436
Preview 6: #8437
Preview 7: #8438
RC 1: #8439
RC 2: #8440

Activity

  1. leecow
    added
    documentation
    on May 3, 2023

  2. WeihanLi commented on May 18, 2023

    @WeihanLi
    WeihanLi
    on May 18, 2023
    Contributor

    @leecow the preview 6 link is incorrect, should be #8437
    The same problem exists in preview 6/7 and rc1/2 issues

  3. mairaw commented on May 18, 2023

    @mairaw
    mairaw
    on May 18, 2023
    Contributor

    Good catch @WeihanLi. I've fixed those.

  4. JonDouglas commented on May 31, 2023

    @JonDouglas
    JonDouglas
    on May 31, 2023
    Collaborator

    .NET Framework -> .NET 7 -> .NET 8 Benchmarks

    Method Runtime Mean Error StdDev
    BuildConsole .NET 7.0 766.1 us 9.20 us 8.61 us
    BuildRegex .NET 7.0 185,561.0 us 3,341.04 us 5,000.71 us
    BuildCompiler .NET 7.0 964,543.7 us 19,287.08 us 27,037.80 us
    BuildConsole .NET 8.0 761.5 us 14.77 us 16.42 us
    BuildRegex .NET 8.0 176,244.4 us 2,601.66 us 4,417.81 us
    BuildCompiler .NET 8.0 944,589.2 us 18,860.02 us 51,629.00 us
    BuildConsole .NET Framework 4.8.1 1,094.1 us 10.63 us 8.88 us
    BuildRegex .NET Framework 4.8.1 410,393.0 us 7,304.48 us 6,099.57 us
    BuildCompiler .NET Framework 4.8.1 2,044,387.2 us 40,654.16 us 48,395.89 us

    // * Warnings *
    MultimodalDistribution
    CompilationBenchmak.BuildCompiler: Runtime=.NET 8.0, Server=True -> It seems that the distribution is bimodal (mValue = 3.44)

    Simplified

    μs .NET Framework 4.8.1 .NET 7.0 .NET 8.0
    Build Hello World 1,094.10 766.1 (-30.0%) 761.5 (-30.4%)
    Build simple app 410,393.00 185,561.0 (-54.8%) 176,244.4 (-57.1%)
    Build Roslyn 2,044,387.20 964,543.7 (-52.8%) 944,589.2 (-53.8%)

    Source: https://gist.github.com/jaredpar/f2fd4c87917ed0de73981a5ea410015e

  5. tarekgh commented on Jun 5, 2023

    @tarekgh
    tarekgh
    on Jun 5, 2023
    Member

    Enhancements to Metrics APIs

    Introducing supplementary metrics APIs to cater to new use cases:

    DI Friendly metrics APIs

    Introducing the IMeterFactory interface that can be registered in DI containers and utilized to create Meter objects in an isolated manner.

                // services is the DI IServiceCollection 
            // Register the IMeterFactory to the DI container using the default meter factory implementation. 
            services.AddMetrics();

    Consumers now have the ability to obtain the meter factory and utilize it for creating a new Meter object.

                IMeterFactory meterFactory = serviceProvider.GetRequiredService<IMeterFactory>();

            MeterOptions options = new MeterOptions("MeterName")
            {
                 Version = "version",
            };

            Meter meter = meterFactory.Create(options);

    Enabling the creation of Meters and Instruments with Tags

    Introducing the capability to attach key-value pair tags to Meters and Instruments during their creation. This feature allows aggregators of published metric measurements to utilize the tags to differentiate the aggregated values based on these tags.

                MeterOptions options = new MeterOptions("name")
            {
                Version = "version",
                
                // Attach these tags to the created meter
                Tags = new TagList() { { "MeterKey1", "MeterValue1" }, { "MeterKey2", "MeterValue2" } }
            };

            Meter meter = meterFactory.Create(options);
            
            Instrument instrument = meter.CreateCounter<int>("counter", null, null, new TagList() { { "counterKey1", "counterValue1" } });
            instrument. Add(1);

    References

    dotnet/runtime#77514 (comment)
    dotnet/runtime#84321
    dotnet/runtime#86740

    Please note that the newly exposed APIs are currently undergoing refinements, which may lead to minor changes in their current exposed form.

  6. baronfel commented on Jun 6, 2023

    @baronfel
    baronfel
    on Jun 6, 2023
    Member

    SDK: SourceLink is part of the .NET SDK!

    The PR is dotnet/sdk#31632

    The .NET SDK now includes SourceLink to help power-up the IDE experience when inspecting Sourcelinked NuGet Packages. The goal is that by bundling SourceLink into the SDK, instead of requiring a separate PackageReference for the package, more packages will include this information by default, resulting in better IDE experiences for developers all-up.

    Source Link is a language- and source-control agnostic system for providing first-class source debugging experiences for binaries. The goal of the project is to enable anyone building NuGet libraries to provide source debugging for their users with almost no effort. Microsoft libraries, such as .NET Core and Roslyn have enabled Source Link. Source Link is supported by Microsoft.

    Visual Studio, and many other editors, support reading Source Link information from symbols while debugging. Editors can download and display the appropriate commit-specific source for users, such as from raw.githubusercontent, enabling breakpoints and all other sources debugging experience on arbitrary NuGet dependencies.

    The shipped implementation of SourceLink includes providers for git, GitHub, GitLab, Azure Repositories, and BitBucket, but there are a other providers available on NuGet. You can find more information about SourceLink at the Learn docs, and read more about the available settings the repo documentation.

  7. AndyAyersMS commented on Jun 8, 2023

    @AndyAyersMS
    AndyAyersMS
    on Jun 8, 2023
    Member

    Codegen

    @JonDouglas @JeremyLikness feel free to craft away....

    Dynamic PGO is now enabled by default. Special configuration settings are no longer needed. We anticipate performance for a broad class of applications will improve by anywhere from 5% to 500% (with 15% a reasonable expectation), depending upon the nature of application bottlenecks. In our local benchmark suite of approximately 4600 tests, 23% improved by 20% or more.

    Customer experience with PGO in past releases has been uniformly positive.

    If you are new to Dynamic PGO we look forward to hearing about your experiences as well (good or bad).

    If necessary, you can opt out of Dynamic PGO via

    <TieredPGO>false</TieredPGO>

    in your .csproj or via similar settings in the runtime config or environment.

  8. ashnaga commented on Jun 8, 2023

    @ashnaga
    ashnaga
    on Jun 8, 2023
    Member

    Linux distribution-built (source-build) SDK now has the capability to build self-contained applications utilizing the source-build runtime packages. Distribution specific runtime package will be bundled with the source-build SDK. During self-contained deployment, this bundled runtime package will be referenced and thereby enabling the feature for the user. Please note that there are no changes for the MS-built SDK. 

    Thanks to our Red Hat partners, especially @tmds, for the valuable contribution to enable this feature.  

  9. baronfel commented on Jun 8, 2023

    @baronfel
    baronfel
    on Jun 8, 2023
    Member

    SDK: Runtime-specific apps no longer self-contained by default

    Since .NET 6, specifying a runtime during publish has resulted in the following warning:

    warning NETSDK1179: One of '--self-contained' or '--no-self-contained' options are required when '--runtime' is used.

    For .NET 8, we're finally taking the step of making this change. Going forward, for apps targeting net8.0 and higher Target Frameworks, -r/--runtime will no longer imply --self-contained. If you intended that behavior you'll either need to

    • add the CLI option explicitly, or
    • add the <SelfContained>true</SelfContained> property to your project files

    Apps targeting net7.0 or lower remain unaffected. You can read more about this change in the breaking change notice we've posted.

    We're making this change because we believe that targeting a specific platforms is an independent decision from bundling the runtime for that platform. Defaulting more apps to framework-dependent deployments means that the runtime the app runs on can be safely updated without requiring a rebuild or redeployment. It also results in smaller app sizes than self-contained deployments.

  10. ivdiazsa commented on Jun 9, 2023

    @ivdiazsa
    ivdiazsa
    on Jun 9, 2023

    Alpine ASP.NET Docker Composite Images

    Introducing a new flavor of ASP.NET Docker Images: The Composites.

    What are the composite images?

    As part of the containerization performance efforts, we are now offering a new ASP.NET Alpine-based Docker image with a composite version of the runtime in Preview 5. This composite is built by compiling multiple MSIL assemblies into a single R2R output binary. Due to having these assemblies embedded into a single image, we save jitting time and thus boosting the startup performance of apps. The other big advantage of the composite over the regular ASP.NET image is that the composites have a smaller size on disk. However, all these benefits don't come without a caveat. Since composites have multiple assemblies embedded into one, they have tighter version coupling. This means the final app run cannot use custom versions of framework and/or ASP.NET binaries embedded into the composite one.

    Where can we get the composite images?

    As of now, the composite images are available as preview in under the mcr.microsoft.com/dotnet/nightly/aspnet repo. The tags are listed with the -composite suffix in the official nightly Dotnet Docker page.

    Future Work

    Right now, the composites are only based on Alpine. Based on feedback as they start getting a more widespread adoption, we have plans to enable them for distroless images, and longer term bigger distros like Ubuntu and Debian.

  11. JulieLeeMSFT commented on Jun 9, 2023

    @JulieLeeMSFT
    JulieLeeMSFT
    on Jun 9, 2023
    Member

    CodeGen

    Community PRs (Many thanks to JIT community contributors!)

    • @SingleAccretion contributed 18 PRs in Preview 5. Much of this work was focused on internal JIT cleanup with the eventual goal of greatly simplifying the internal representation (IR), in particular around the representation of assignments/stores.
      • PR#85180 marked the start of this work and in a future preview it will result in the JIT being several percent faster when compiling user functions.
    • @yesmey enabled unrolling StringBuilder.Append for const string that unblocks more AVX-512 usages. It imporved the execution time of System.Tests.Perf_Enum benchmarks up to 8 % and StringBuilder up to 16%, PR#85894.
    • @MichalPetryka submitted PR#85398 that improved the JIT’s ability to reason about single-defined variables early-on, and PR#85349 that improved the JIT’s codegen for calls to function pointers without arguments.

    AVX-512

    • PR#85389 enabled AVX-512 for block unrollings, which increases ranges where it previously used to fallback to memcpy/memset and reduced the execution time by half.
    • Various integer intrinsics are enabled for AVX512F, AVX512BW and AVX512CD, PR#85833.

    NativeAOT: Optimized ThreadStatic field access for GC-type

    In preview 4, with PR#82973, we optimized the field accesses that are marked as ThreadStaticLocal for primitive types. With This PR#85619, we started optimizing the GC fields as well. This gave us some really good improvements in various microbenchmarks (133 on windows/arm64, 23 on windows/x64, 16, 13, 11 improvements).

    Arm64

    In preview 5, we enabled a few peephole optimizations:

    • With PR#85032 , we enabled peephole optimization to replace str pair with stp.
    • With PR#85657, we enabled peephole optimization of replacing pair of ldr/str with ldp/stp inside prolog.

    General optimizations

    • x64 instructions such as movzx, movsx and movsxd have been optimized in PR#85780, which slightly improved code-gen by eliminating more redundant mov instructions.
    • PR#86318 improved constant folding for some frozen objects (non-GC objects). It reduced the size of the generated code by almost 10 times (e.g., 424 bytes to 41 byte).

  12. elinor-fung commented on Jun 9, 2023

    @elinor-fung
    elinor-fung
    on Jun 9, 2023
    Member

    Runtime host determines RID-specific assets without RID graph by default

    When running an application with RID-specific assets, the host determines which assets are relevant for the platform on which it's running. This applies to both the application itself and the resolution logic used by AssemblyDependencyResolver. By default in .NET 8, this determination will no longer use the RID graph, but will rely on a known list of RIDs based on how the runtime itself was built.

    The RID graph has proven to be costly to maintain, difficult to understand, and generally fragile. This change is part of a longer-term goal to simplify our RID model.

    You can read more about this change in the breaking change notice.

  13. buyaa-n commented on Jun 11, 2023

    @buyaa-n
    buyaa-n
    on Jun 11, 2023
    Contributor

    .NET Libraries analyzers

    Starting from .NET 8 preview 1, we have added several analyzers and code fixers that help developers verify correct and/or more performant usage of .NET Library APIs. We are thrilled to mention that most of these analyzers have been implemented by our community members. We would like to extend a big thank you to all our contributors for their hard work and dedication.

    Analyzer proposal and the contributor Description Category Severity Help Link
    Pass constants to parameters marked as [ConstantExpected] by @wzchua CA1856 fires when the ConstantExpected attribute not applied correctly on the parameter. CA1857 fires when a parameter annotated with the ConstantExpected attribute but the argument provided is not a constant, a constants should be used for optimal performance. Performance CA1856: Error CA1857: Warning CA1856, CA1857
    Using StartsWith instead of IndexOf == 0 by @Youssef1313 It's more efficient and clearer to call String.StartsWith than to call String.IndexOf and compare the result with zero to determine whether a string starts with a given prefix. Performance Info ca1858
    Recommend use of concrete types to maximize devirtualization potential by @geeknoid This rule recommends upgrading the type of specific local variables, fields, properties, method parameters, and method return types from interface or abstract types to concrete types when possible. Using concrete types leads to higher quality generated code by minimizing virtual or interface dispatch overhead and enabling inlining. Performance Info CA1859
    Prefer .Length/Count/IsEmpty over Any() by @CollinAlpert It's more efficient and clearer to use Length, Count, or IsEmpty than to call Enumerable.Any extenion method to determine whether a collection type has any elements Performance Info CA1860
    Extract array of const to static readonly field @steveberdy Constant arrays passed as arguments are not reused when called repeatedly, which implies a new array is created each time. If the passed array is not mutated within the called method, consider extracting it to a static readonly field to improve performance. Performance Info CA1861
    Do not use OfType() with impossible types by @fowl2 Enumerable.Cast<T> and Enumerable.OfType<T> require compatible types to function expectedly. Enumerable.Cast<T> will throw InvalidCastException at runtime for elements of incompatible types. Enumerable.OfType<T> will never succeed with elements of incompatible types, resulting in an empty sequence. Widening and user defined conversions are not supported with generic types. Reliability Warning CA2021
    Convert argument null checks to ArgumentNullException.ThrowIfNull by @stephentoub Throw helpers are simpler and more efficient than an if block constructing a new exception instance. With this analyzer four analyzers added for: ArgumentNullException, ArgumentException, ArgumentOutOfRangeException and ObjectDisposedException throw helpers Maintainability Info CA1510, CA1511, CA1512, CA1513

    We plan to continue adding more analyzers to .NET 8 to help developers write better code and we are hoping for even more community contributions. This is a great opportunity for the community to add a new complete feature to .NET 8 SDK.

    If you are interested in contributing, please check out our list of analyzers that are ready for development and marked up for grabs.

  14. leslierichardson95 commented on Jun 12, 2023

    @leslierichardson95
    leslierichardson95
    on Jun 12, 2023

    Improve your productivity in VS Code with the C# Dev Kit extension!

    The C# Dev Kit extension in VS Code is now available for public preview in VS Code! Designed to improve your C# productivity in VS Code, C# Dev Kit helps you manage your code with a solution explorer, write code faster with AI-assisted suggestions and completions, and gives you new capabilities to run and debug tests in the Test Explorer. Using a Roslyn-powered language service, C# Dev Kit also greatly improves performance of C# language features such as code navigation, refactoring, IntelliSense, and more.

    To get started with C# Dev Kit, check out our recent announcement blog post.

  15. omajid commented on Jun 20, 2023

    @omajid
    omajid
    on Jun 20, 2023
    Member

    Linux distribution-built (source-build) SDK now has the capability to build self-contained applications utilizing the source-build runtime packages.

    I don't think this feature landed in Preview 5 itself. It was implemented during Preview 5 period, and it appears to be a part of the nightly Preview 6 builds, but I can't see it in Preview 5.

    Preview 5:

    $ ls -1 packs/
Microsoft.AspNetCore.App.Ref
Microsoft.NETCore.App.Host.fedora.38-x64
Microsoft.NETCore.App.Ref
NETStandard.Library.Ref

    Preview 6 (nightly):

    $ tar tf artifacts/x64/Release/dotnet-sdk-8.0.100-preview.6.23319.1-fedora.38-x64.tar.gz | grep './packs/' | cut -d/ -f-4 | sort -u
./packs/
./packs/Microsoft.AspNetCore.App.Ref/
./packs/Microsoft.AspNetCore.App.Ref/8.0.0-preview.6.23316.5
./packs/Microsoft.AspNetCore.App.Runtime.fedora.38-x64/
./packs/Microsoft.AspNetCore.App.Runtime.fedora.38-x64/8.0.0-preview.6.23316.5
./packs/Microsoft.NETCore.App.Host.fedora.38-x64/
./packs/Microsoft.NETCore.App.Host.fedora.38-x64/8.0.0-preview.6.23316.3
./packs/Microsoft.NETCore.App.Ref/
./packs/Microsoft.NETCore.App.Ref/8.0.0-preview.6.23316.3
./packs/Microsoft.NETCore.App.Runtime.fedora.38-x64/
./packs/Microsoft.NETCore.App.Runtime.fedora.38-x64/8.0.0-preview.6.23316.3
./packs/NETStandard.Library.Ref/
./packs/NETStandard.Library.Ref/2.1.0

  16. JonDouglas commented on Jun 27, 2023

    @JonDouglas
    JonDouglas
    on Jun 27, 2023
    Collaborator

    Complete via https://devblogs.microsoft.com/dotnet/announcing-dotnet-8-preview-5/

  17. JonDouglas
    closed this as completedon Jun 27, 2023
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