using System;
using System.Threading;
using System.Threading.Tasks;
using Microsoft.Extensions.Caching.Memory;

namespace cache_repro
{
    class Program
    {
        static bool _evicted;

        static async Task Main(string[] args)
        {
            var cache = new MemoryCache(new MemoryCacheOptions());
            var key = new object();

            var cts = new CancellationTokenSource(TimeSpan.FromSeconds(2));

            cache.Set(key, new object(), new MemoryCacheEntryOptions
            {
                ExpirationTokens = { new Microsoft.Extensions.Primitives.CancellationChangeToken(cts.Token) },
                PostEvictionCallbacks = { new PostEvictionCallbackRegistration { EvictionCallback = OnEntryEvicted } },
            });

            System.Console.WriteLine(cache.TryGetValue(key, out _));

            await Task.Delay(TimeSpan.FromSeconds(5));
            System.Console.WriteLine(cache.TryGetValue(key, out _));
            System.Console.WriteLine($"Evicted: {_evicted}");
        }

        static void OnEntryEvicted(object key, object value, EvictionReason reason, object state)
        {
            _evicted = true;
        }
    }
}