update libraries

docs/core/whats-new/dotnet-9/libraries.md

@@ -2,12 +2,12 @@
 title: What's new in .NET libraries for .NET 9
 description: Learn about the new .NET libraries features introduced in .NET 9.
 titleSuffix: ""
-ms.date: 04/11/2024
+ms.date: 05/21/2024
 ms.topic: whats-new
 ---
 # What's new in .NET libraries for .NET 9
 
-This article describes new features in the .NET libraries for .NET 9. It's been updated for .NET 9 Preview 3.
+This article describes new features in the .NET libraries for .NET 9. It's been updated for .NET 9 Preview 4.
 
 ## Serialization
 
@@ -84,20 +84,36 @@ KMAC is available on Linux with OpenSSL 3.0 or later, and on Windows 11 Build 26
 
 ## Reflection
 
+### Persisted assemblies
+
 In .NET Core versions and .NET 5-8, support for building an assembly and emitting reflection metadata for dynamically created types was limited to a runnable <xref:System.Reflection.Emit.AssemblyBuilder>. The lack of support for *saving* an assembly was often a blocker for customers migrating from .NET Framework to .NET. .NET 9 adds a new type, `PersistedAssemblyBuilder` <!--<xref:System.Reflection.Emit.AssemblyBuilder.PersistedAssemblyBuilder>-->, that you can use to save an emitted assembly.
 
 To create a `PersistedAssemblyBuilder` instance, call its constructor and pass the assembly name, the core assembly, `System.Private.CoreLib`, to reference base runtime types, and optional custom attributes. After you emit all members to the assembly, call the `PersistedAssemblyBuilder.Save(string assemblyFileName)` <!--<xref:System.Reflection.Emit.AssemblyBuilder.PersistedAssemblyBuilder.Save(System.String)>--> method to create an assembly with default settings. If you want to set the entry point or other options, you can call `PersistedAssemblyBuilder.GenerateMetadata(System.Reflection.Metadata.BlobBuilder,System.Reflection.Metadata.BlobBuilder)` <!--<xref:System.Reflection.Emit.AssemblyBuilder.PersistedAssemblyBuilder.GenerateMetadata(System.Reflection.Metadata.BlobBuilder,System.Reflection.Metadata.BlobBuilder)>--> and use the metadata it returns to save the assembly. The following code shows an example of creating a persisted assembly and setting the entry point.
 
 :::code language="csharp" source="../snippets/dotnet-9/csharp/Reflection.cs" id="SaveAssembly":::
 
-## New TimeSpan.From\* overloads
+The new <xref:System.Reflection.Emit.PersistedAssemblyBuilder> class includes PDB support. You can emit symbol info and use it to debug a generated assembly. The API has a similar shape to the .NET Framework implementation. For more information, see [Emit symbols and generate PDB](../../../fundamentals/runtime-libraries/system-reflection-emit-persistedassemblybuilder.md#emit-symbols-and-generate-pdb).
+
+## Date and time
+
+### New TimeSpan.From\* overloads
 
 The <xref:System.TimeSpan> class offers several `From*` methods that let you create a `TimeSpan` object using a `double`. However, since `double` is a binary-based floating-point format, [inherent imprecision can lead to errors](https://github.com/dotnet/runtime/issues/93890). For instance, `TimeSpan.FromSeconds(101.832)` might not precisely represent `101 seconds, 832 milliseconds`, but rather approximately `101 seconds, 831.9999999999936335370875895023345947265625 milliseconds`. This discrepancy has caused frequent confusion, and it's also not the most efficient way to represent such data. To address this, .NET 9 adds new overloads that let you create `TimeSpan` objects from integers. There are new overloads from `FromDays`, `FromHours`, `FromMinutes`, `FromSeconds`, `FromMilliseconds`, and `FromMicroseconds`.
 
 The following code shows an example of calling the `double` and one of the new integer overloads.
 
 :::code language="csharp" source="../snippets/dotnet-9/csharp/TimeSpan.cs" id="TimeSpan.From":::
 
-## `ActivatorUtilities.CreateInstance` constructor
+## Dependency injection
+
+### `ActivatorUtilities.CreateInstance` constructor
 
 The constructor resolution for <xref:Microsoft.Extensions.DependencyInjection.ActivatorUtilities.CreateInstance%2A?displayProperty=nameWithType> has changed in .NET 9. Previously, a constructor that was explicitly marked using the <xref:Microsoft.Extensions.DependencyInjection.ActivatorUtilitiesConstructorAttribute> attribute might not be called, depending on the ordering of constructors and the number of constructor parameters. The logic has changed in .NET 9 such that a constructor that has the attribute is always called.
+
+## Diagnostics
+
+### New Activity.AddLink method
+
+Previously, you could only link a tracing <xref:System.Diagnostics.Activity> to other tracing contexts when you [created the `Activity`](xref:System.Diagnostics.ActivitySource.CreateActivity(System.String,System.Diagnostics.ActivityKind,System.Diagnostics.ActivityContext,System.Collections.Generic.IEnumerable{System.Collections.Generic.KeyValuePair{System.String,System.Object}},System.Collections.Generic.IEnumerable{System.Diagnostics.ActivityLink},System.Diagnostics.ActivityIdFormat)?displayProperty=nameWithType). New in .NET 9, the `Activity.AddLink(System.Diagnostics.ActivityLink)` <!--<xref:System.Diagnostics.Activity.AddLink(System.Diagnostics.ActivityLink)>--> API lets you link an `Activity` object to other tracing contexts after it's created. This change aligns with the [OpenTelemetry specifications](https://github.com/open-telemetry/opentelemetry-specification/blob/6360b49d20ae451b28f7ba0be168ed9a799ac9e1/specification/trace/api.md?plain=1#L804) as well.
+
+:::code language="csharp" source="../snippets/dotnet-9/csharp/Diagnostics.cs" id="AddLink":::

docs/core/whats-new/dotnet-9/runtime.md

@@ -7,7 +7,7 @@ ms.topic: whats-new
 ---
 # What's new in the .NET 9 runtime
 
-This article describes the performance enhancements in the .NET runtime for .NET 9. It's been updated for .NET 9 Preview 3.
+This article describes the performance enhancements in the .NET runtime for .NET 9. It's been updated for .NET 9 Preview 4.
 
 ## Loop optimizations
 

docs/core/whats-new/dotnet-9/sdk.md

@@ -7,7 +7,7 @@ ms.topic: whats-new
 ---
 # What's new in the SDK for .NET 9
 
-This article describes new features in the .NET SDK for .NET 9. It's been updated for .NET 9 Preview 3.
+This article describes new features in the .NET SDK for .NET 9. It's been updated for .NET 9 Preview 4.
 
 ## Unit testing
 

docs/core/whats-new/snippets/dotnet-9/csharp/Diagnostics.cs

@@ -0,0 +1,16 @@
+
+using System.Diagnostics;
+
+internal class Diagnostics
+{
+    public static void RunIt()
+    {
+        // <AddLink>
+        ActivityContext activityContext = new(ActivityTraceId.CreateRandom(), ActivitySpanId.CreateRandom(), ActivityTraceFlags.None);
+        ActivityLink activityLink = new(activityContext);
+
+        Activity activity = new("LinkTest");
+        activity.AddLink(activityLink);
+        // </AddLink>
+    }
+}

docs/core/whats-new/snippets/dotnet-9/csharp/Reflection.cs

@@ -53,9 +53,9 @@ out BlobBuilder fieldData
     public static void UseAssembly(string assemblyPath)
     {
         Assembly assembly = Assembly.LoadFrom(assemblyPath);
-        Type type = assembly.GetType("MyType");
-        MethodInfo method = type.GetMethod("SumMethod");
-        Console.WriteLine(method.Invoke(null, [5, 10]));
+        Type? type = assembly.GetType("MyType");
+        MethodInfo? method = type?.GetMethod("SumMethod");
+        Console.WriteLine(method?.Invoke(null, [5, 10]));
     }
     // </SaveAssembly>
 }

docs/machine-learning/whats-new/overview.md

@@ -49,15 +49,15 @@ The following examples show how to use the `Tiktoken` text tokenizer.
 
 The following examples show how to use the `Llama` text tokenizer.
 
-:::code language="csharp" source="./snippets/csharp/LlamaTokenizer.cs" id="Llama":::
+:::code language="csharp" source="./snippets/csharp/Llama.cs" id="Llama":::
 
 The following examples show how to use the `CodeGen` tokenizer.
 
-:::code language="csharp" source="./snippets/csharp/CodeGenTokenizer.cs" id="CodeGen":::
+:::code language="csharp" source="./snippets/csharp/CodeGen.cs" id="CodeGen":::
 
 The following example demonstrates how to use the tokenizer with `Span<char>` and how to disable normalization or pretokenization on the encoding calls.
 
-:::code language="csharp" source="./snippets/csharp/LlamaTokenizer.cs" id="Span":::
+:::code language="csharp" source="./snippets/csharp/Llama.cs" id="Span":::
 
 ## Model Builder (Visual Studio extension)