<PackageReference Include="System.Reactive" Version="6.0.0-preview.16" />

System.Reactive.HalfSerializer

static class HalfSerializer
Utility methods for dealing with serializing OnXXX signals for an IObserver where concurrent OnNext is still not allowed but concurrent OnError/OnCompleted may happen. This serialization case is generally lower overhead than a full SerializedObserver wrapper and doesn't need allocation.
namespace System.Reactive { internal static class HalfSerializer { public static void ForwardOnNext<[System.Runtime.CompilerServices.Nullable(2)] T>(ISink<T> sink, T item, ref int wip, ref Exception error); public static void ForwardOnError<[System.Runtime.CompilerServices.Nullable(2)] T>(ISink<T> sink, Exception ex, ref int wip, ref Exception error); public static void ForwardOnCompleted<T>(ISink<T> sink, ref int wip, ref Exception error); } }