Startup.cs

using System;
using System.Diagnostics;
using System.Text.Json;
using System.IO;
using System.Buffers;

#if SERIALIZER_NEW
using System.Text.Json.Serialization;
using System.Text.Json.Serialization.Metadata;
using Startup;
#endif

namespace Startup
{
    class Program
    {
        private static byte[] s_serialized = new byte[] { 123, 34, 109, 101, 115, 115, 97, 103, 101, 34, 58, 34, 72, 101, 108, 108, 111, 44, 32, 87, 111, 114, 108, 100, 33, 34, 125 };
        private static JsonMessage message = new JsonMessage { message = "Hello, World!" };

#if SERIALIZER_OLD
        private static JsonSerializerOptions s_oldPatternOptions = new();
#elif SERIALIZER_NEW
        private static JsonTypeInfo<JsonMessage> s_newPatternMetadata = JsonContext.Default.JsonMessage;
#endif

        static void Main(string[] args)
        {
            Stopwatch sw = new();

            Process process = Process.GetCurrentProcess();
            process.Refresh();
            long oldPrivateBytes = process.PrivateMemorySize64 / 1024;

            sw.Start();

#if SERIALIZE
            RunSerializeBenchMark();
#else
            RunDeserializeBenchMark();
#endif

            sw.Stop();
            process.Refresh();

            long newPrivateBytes = process.PrivateMemorySize64 / 1024;
            Console.Write("Private bytes (KB): ");
            Console.WriteLine(newPrivateBytes - oldPrivateBytes);

            Console.Write("Elapsed time (ms):");
            Console.WriteLine(sw.ElapsedMilliseconds);
        }

        private static void RunSerializeBenchMark()
        {
            using MemoryStream ms = new();
            using Utf8JsonWriter writer = new(ms);

#if SERIALIZER_OLD
            JsonSerializer.Serialize(writer, message, s_oldPatternOptions);
#elif SERIALIZER_NEW
            JsonSerializer.Serialize(writer, message, s_newPatternMetadata);
#endif
        }

        private static void RunDeserializeBenchMark()
        {
#if SERIALIZER_OLD
            _ = JsonSerializer.Deserialize<JsonMessage>(s_serialized, s_oldPatternOptions);
#elif SERIALIZER_NEW
            _ = JsonSerializer.Deserialize(s_serialized, s_newPatternMetadata);
#endif
        }
    }

    public class JsonMessage
    {
        public string message { get; set; }
    }

#if SERIALIZER_NEW
    [JsonSerializable(typeof(JsonMessage))]
    internal partial class JsonContext : JsonSerializerContext { }
#endif
}