address feedback

src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonSerializerOptions.Caching.cs

@@ -73,11 +73,7 @@ internal void ClearCaches()
 
         private void InitializeCachingContext()
         {
-#if NETCOREAPP
             _cachingContext = TrackedCachingContexts.GetOrCreate(this);
-#else
-            _cachingContext = new CachingContext(this);
-#endif
         }
 
         /// <summary>
@@ -111,7 +107,6 @@ public void Clear()
             }
         }
 
-#if NETCOREAPP
         /// <summary>
         /// Defines a cache of CachingContexts; instead of using a ConditionalWeakTable which can be slow to traverse
         /// this approach uses a regular dictionary pointing to weak references of <see cref="CachingContext"/>.
@@ -226,7 +221,7 @@ static int EstimateEvictionRunsToSkip(int latestEvictionCount)
 
                         // - If avgEvictionsPerRun >= 1 we skip no subsequent eviction calls.
                         // - If avgEvictionsPerRun < 1 we skip ~ `1 / avgEvictionsPerRun` calls.
-                        int runsPerEviction = (int)Math.Round(1 / Math.Clamp(avgEvictionsPerRun, 0.1, 1));
+                        int runsPerEviction = (int)Math.Round(1 / Math.Min(Math.Max(avgEvictionsPerRun, 0.1), 1));
                         Debug.Assert(runsPerEviction >= 1 && runsPerEviction <= 10);
                         return runsPerEviction - 1;
                     }
@@ -315,7 +310,18 @@ public int GetHashCode(JsonSerializerOptions options)
 
                 return hc.ToHashCode();
             }
-        }
+
+#if !NETCOREAPP
+            /// <summary>
+            /// Polyfill for System.HashCode.
+            /// </summary>
+            private struct HashCode
+            {
+                private int _hashCode;
+                public void Add<T>(T? value) => _hashCode = (_hashCode, value).GetHashCode();
+                public int ToHashCode() => _hashCode;
+            }
 #endif
+        }
     }
 }

src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonSerializerOptions.Converters.cs

@@ -93,7 +93,7 @@ void Add(JsonConverter converter) =>
         /// </remarks>
         public IList<JsonConverter> Converters { get; }
 
-        internal JsonConverter GetConverterForMember(Type? parentClassType, Type runtimePropertyType, MemberInfo? memberInfo)
+        internal JsonConverter GetConverterFromMember(Type? parentClassType, Type runtimePropertyType, MemberInfo? memberInfo)
         {
             JsonConverter converter = null!;
 

src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Metadata/JsonTypeInfo.cs

@@ -600,7 +600,7 @@ private static JsonConverter GetConverter(
             Debug.Assert(type != null);
             ValidateType(type, parentClassType, memberInfo, options);
 
-            JsonConverter converter = options.GetConverterForMember(parentClassType, type, memberInfo);
+            JsonConverter converter = options.GetConverterFromMember(parentClassType, type, memberInfo);
 
             // The runtimeType is the actual value being assigned to the property.
             // There are three types to consider for the runtimeType:

src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Metadata/ReflectionEmitCachingMemberAccessor.Cache.cs

@@ -13,9 +13,9 @@ internal sealed partial class ReflectionEmitCachingMemberAccessor
     {
         private sealed class Cache<TKey> where TKey : notnull
         {
-            private int _lock;
-            private long _lastEvictedTicks; // tracks total number of invocations to the cache; can be allowed to overflow.
-            private readonly long _evictionIntervalTicks; // number of cache invocations needed before triggering an eviction run.
+            private int _evictLock;
+            private long _lastEvictedTicks; // timestamp of latest eviction operation.
+            private readonly long _evictionIntervalTicks; // min timespan needed to trigger a new evict operation.
             private readonly long _slidingExpirationTicks; // max timespan allowed for cache entries to remain inactive.
             private readonly ConcurrentDictionary<TKey, CacheEntry> _cache = new();
 
@@ -28,7 +28,8 @@ public Cache(TimeSpan slidingExpiration, TimeSpan evictionInterval)
 
             public TValue GetOrAdd<TValue>(TKey key, Func<TKey, TValue> valueFactory) where TValue : class?
             {
-                CacheEntry entry = _cache.GetOrAdd(key,
+                CacheEntry entry = _cache.GetOrAdd(
+                    key,
 #if NETCOREAPP
                     static (TKey key, Func<TKey, TValue> valueFactory) => new(valueFactory(key)),
                     valueFactory);
@@ -40,14 +41,15 @@ public TValue GetOrAdd<TValue>(TKey key, Func<TKey, TValue> valueFactory) where
 
                 if (utcNowTicks - Volatile.Read(ref _lastEvictedTicks) >= _evictionIntervalTicks)
                 {
-                    if (Interlocked.CompareExchange(ref _lock, 1, 0) == 0)
+                    if (Interlocked.CompareExchange(ref _evictLock, 1, 0) == 0)
                     {
                         if (utcNowTicks - _lastEvictedTicks >= _evictionIntervalTicks)
                         {
                             EvictStaleCacheEntries(utcNowTicks);
                             Volatile.Write(ref _lastEvictedTicks, utcNowTicks);
-                            Volatile.Write(ref _lock, 0);
                         }
+
+                        Volatile.Write(ref _evictLock, 0);
                     }
                 }
 

src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Metadata/ReflectionEmitCachingMemberAccessor.cs

@@ -19,7 +19,7 @@ internal sealed partial class ReflectionEmitCachingMemberAccessor : MemberAccess
         public override Action<TCollection, object?> CreateAddMethodDelegate<[DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicMethods)] TCollection>()
             => s_cache.GetOrAdd((nameof(CreateAddMethodDelegate), typeof(TCollection), null),
                 [UnconditionalSuppressMessage("ReflectionAnalysis", "IL2091:UnrecognizedReflectionPattern",
-                    Justification = "DynamicallyAccessedMembersAttribute is not inherited by scoped generic parameter in lambda body.")]
+                    Justification = "Parent method annotation does not flow to lambda method, cf. https://github.com/dotnet/roslyn/issues/46646")]
                 static (_) => s_sourceAccessor.CreateAddMethodDelegate<TCollection>());
 
         public override JsonTypeInfo.ConstructorDelegate? CreateConstructor([DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] Type classType)
@@ -38,14 +38,14 @@ public override Action<object, TProperty> CreateFieldSetter<TProperty>(FieldInfo
         public override Func<IEnumerable<KeyValuePair<TKey, TValue>>, TCollection> CreateImmutableDictionaryCreateRangeDelegate<TCollection, TKey, TValue>()
             => s_cache.GetOrAdd((nameof(CreateImmutableDictionaryCreateRangeDelegate), typeof((TCollection, TKey, TValue)), null),
                 [UnconditionalSuppressMessage("ReflectionAnalysis", "IL2026:RequiresUnreferencedCode",
-                    Justification = "Factory method calls into chained RequiresUnreferencedCode method.")]
+                    Justification = "Parent method annotation does not flow to lambda method, cf. https://github.com/dotnet/roslyn/issues/46646")]
                 static (_) => s_sourceAccessor.CreateImmutableDictionaryCreateRangeDelegate<TCollection, TKey, TValue>());
 
         [RequiresUnreferencedCode(IEnumerableConverterFactoryHelpers.ImmutableConvertersUnreferencedCodeMessage)]
         public override Func<IEnumerable<TElement>, TCollection> CreateImmutableEnumerableCreateRangeDelegate<TCollection, TElement>()
             => s_cache.GetOrAdd((nameof(CreateImmutableEnumerableCreateRangeDelegate), typeof((TCollection, TElement)), null),
                 [UnconditionalSuppressMessage("ReflectionAnalysis", "IL2026:RequiresUnreferencedCode",
-                    Justification = "Factory method calls into chained RequiresUnreferencedCode method.")]
+                    Justification = "Parent method annotation does not flow to lambda method, cf. https://github.com/dotnet/roslyn/issues/46646")]
                 static (_) => s_sourceAccessor.CreateImmutableEnumerableCreateRangeDelegate<TCollection, TElement>());
 
         public override Func<object[], T>? CreateParameterizedConstructor<T>(ConstructorInfo constructor)

src/libraries/System.Text.Json/tests/System.Text.Json.SourceGeneration.Tests/JsonSerializerContextTests.cs

@@ -45,6 +45,9 @@ public static void Converters_AndTypeInfoCreator_NotRooted_WhenMetadataNotPresen
                     AssertFieldNull("s_defaultSimpleConverters", optionsInstance: null);
                     AssertFieldNull("s_defaultFactoryConverters", optionsInstance: null);
 
+                    // Confirm type info dynamic creator not set.
+                    AssertFieldNull("s_typeInfoCreationFunc", optionsInstance: null);
+
                     static void AssertFieldNull(string fieldName, JsonSerializerOptions? optionsInstance)
                     {
                         BindingFlags bindingFlags = BindingFlags.NonPublic | (optionsInstance == null ? BindingFlags.Static : BindingFlags.Instance);