Fix PostEvictionCallbacks bug

src/libraries/Microsoft.Extensions.Caching.Memory/src/CacheEntry.CacheEntryTokens.cs

@@ -23,7 +23,7 @@ private sealed class CacheEntryTokens
             internal List<IChangeToken> ExpirationTokens => _expirationTokens ??= new List<IChangeToken>();
             internal List<PostEvictionCallbackRegistration> PostEvictionCallbacks => _postEvictionCallbacks ??= new List<PostEvictionCallbackRegistration>();
 
-            internal void AttachTokens()
+            internal void AttachTokens(CacheEntry cacheEntry)
             {
                 if (_expirationTokens != null)
                 {
@@ -35,7 +35,7 @@ internal void AttachTokens()
                             if (expirationToken.ActiveChangeCallbacks)
                             {
                                 _expirationTokenRegistrations ??= new List<IDisposable>(1);
-                                IDisposable registration = expirationToken.RegisterChangeCallback(ExpirationCallback, this);
+                                IDisposable registration = expirationToken.RegisterChangeCallback(ExpirationCallback, cacheEntry);
                                 _expirationTokenRegistrations.Add(registration);
                             }
                         }

src/libraries/Microsoft.Extensions.Caching.Memory/src/CacheEntry.cs

@@ -199,7 +199,7 @@ bool FullCheck(in DateTimeOffset offset)
             }
         }
 
-        internal void AttachTokens() => _tokens?.AttachTokens();
+        internal void AttachTokens() => _tokens?.AttachTokens(this);
 
         private static void ExpirationTokensExpired(object obj)
         {

src/libraries/Microsoft.Extensions.Caching.Memory/tests/TokenExpirationTests.cs

@@ -207,6 +207,35 @@ public void TokenExpiresOnRegister()
             Assert.Null(result);
         }
 
+        [Fact]
+        public void PostEvictionCallbacksGetInvokedWhenMemoryCacheEntriesExpireWithAnActiveChangeToken()
+        {
+            using var cache = new MemoryCache(new MemoryCacheOptions());
+            var key = new object();
+
+            var cts = new CancellationTokenSource();
+            var callbackInvoked = new ManualResetEvent(false);
+
+            cache.Set(key, new object(), new MemoryCacheEntryOptions
+            {
+                ExpirationTokens = { new CancellationChangeToken(cts.Token) },
+                PostEvictionCallbacks =
+                {
+                    new PostEvictionCallbackRegistration()
+                    {
+                        EvictionCallback = (key, value, reason, state) => ((ManualResetEvent)state).Set(),
+                        State = callbackInvoked
+                    }
+                }
+            });
+
+            Assert.True(cache.TryGetValue(key, out _));
+
+            cts.Cancel();
+            Assert.True(callbackInvoked.WaitOne(TimeSpan.FromSeconds(10)));
+            Assert.False(cache.TryGetValue(key, out _));
+        }
+
         internal class TestToken : IChangeToken
         {
             private bool _hasChanged;