.NET 5 Preview 3

Here are some of the improvements in Preview 3.

Code quality improvements in RyuJIT

Every release includes a set of changes that improve the machine code that the JIT generates, which is also known as "code quality". Better code quality means better application performance.

• Vectorise BitArray for ARM64: The BitArray class was updated to include a hardware-accelerated implementation for ARM64 using ARM64 intrinsics. The performance improvements for BitArray are very significant.
• Implement simple version of On Stack Replacement (OSR): On-stack replacement (OSR) is a new capability that allows the code executed by currently running methods to be changed in the middle of method execution, while those methods are active "on stack".
• Dynamic generic dictionary expansion feature: Some uses of generics now have better performance based on improving the implementation of low-level dictionaries used by the runtime to store information about generic types and methods.
• Implement Vector.Ceiling / Vector.Floor: Implement Vector.Ceiling / Vector.Floor using x64 and ARM64 intrinsics, per API proposal.
• JIT: allow CORINFO_HELP_READYTORUN_GENERIC_HANDLE to be optimized: Improves code quality for generics in Ready2Run images.
• JIT: enable tail calls and copy omission for implicit by ref structs: Improves code quality for structs as arguments in “tail call” position calls.

System.Text.Json improvements

• Add support for preserve references on JSON: Enables ReferenceLoopHandling, which is one of the key features of JSON.NET serialization.
• Add new System.Net.Http.Json project/namespace: Adds new extension methods for HttpClient that allow serialization from/to JSON.
• Add JsonConstructor and support for deserializing with parameterized ctors: Adds support for immutable classes and structs to JsonSerializer.
• Add JsonIgnoreCondition & per-property ignore logic: Adds support for null value handling, which is another feature of JSON.NET serialization.

.NET SDK Support for .NET Framework Assemblies

The .NET SDK will now auto-reference the Microsoft.NETFramework.ReferenceAssemblies NuGet package given a .NET Framework target framework in a project file. This change enables building .NET Framework projects on a machine without the required .NET Framework targeting pack installed. This improvement is specific to targeting packs and doesn’t account for other dependencies that a project may have.

ASP.NET Core: Performance Improvements to HTTP/2

By significantly reducing allocations in the HTTP/2 code path and adding support for HPack static compression of HTTP/2 response headers in Kestrel, the 5.0.0-prevew3 release improves the performance of HTTP/2.