Use global caching in JsonSerializerOptions

src/libraries/System.Text.Json/src/System.Text.Json.csproj

@@ -121,6 +121,7 @@ System.Text.Json.Nodes.JsonValue</PackageDescription>
     <Compile Include="System\Text\Json\Serialization\JsonSerializer.Write.Element.cs" />
     <Compile Include="System\Text\Json\Serialization\JsonSerializer.Write.Node.cs" />
     <Compile Include="System\Text\Json\Serialization\JsonSerializerContext.cs" />
+    <Compile Include="System\Text\Json\Serialization\JsonSerializerOptions.Caching.cs" />
     <Compile Include="System\Text\Json\Serialization\ReferenceEqualsWrapper.cs" />
     <Compile Include="System\Text\Json\Serialization\ConverterStrategy.cs" />
     <Compile Include="System\Text\Json\Serialization\ConverterList.cs" />
@@ -247,6 +248,8 @@ System.Text.Json.Nodes.JsonValue</PackageDescription>
     <Compile Include="System\Text\Json\Serialization\Metadata\MemberAccessor.cs" />
     <Compile Include="System\Text\Json\Serialization\Metadata\ParameterRef.cs" />
     <Compile Include="System\Text\Json\Serialization\Metadata\PropertyRef.cs" />
+    <Compile Include="System\Text\Json\Serialization\Metadata\ReflectionEmitCachingMemberAccessor.Cache.cs" />
+    <Compile Include="System\Text\Json\Serialization\Metadata\ReflectionEmitCachingMemberAccessor.cs" />
     <Compile Include="System\Text\Json\Serialization\Metadata\ReflectionEmitMemberAccessor.cs" />
     <Compile Include="System\Text\Json\Serialization\Metadata\ReflectionMemberAccessor.cs" />
     <Compile Include="System\Text\Json\Serialization\MetadataPropertyName.cs" />

src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonSerializer.Helpers.cs

@@ -18,12 +18,12 @@ private static JsonTypeInfo GetTypeInfo(JsonSerializerOptions? options, Type run
             Debug.Assert(runtimeType != null);
 
             options ??= JsonSerializerOptions.Default;
-            if (!options.IsInitializedForReflectionSerializer)
+            if (!JsonSerializerOptions.IsInitializedForReflectionSerializer)
             {
-                options.InitializeForReflectionSerializer();
+                JsonSerializerOptions.InitializeForReflectionSerializer();
             }
 
-            return options.GetOrAddClassForRootType(runtimeType);
+            return options.GetOrAddJsonTypeInfoForRootType(runtimeType);
         }
 
         private static JsonTypeInfo GetTypeInfo(JsonSerializerContext context, Type type)

src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonSerializer.Read.Stream.cs

@@ -287,9 +287,9 @@ public static partial class JsonSerializer
             CancellationToken cancellationToken = default)
         {
             options ??= JsonSerializerOptions.Default;
-            if (!options.IsInitializedForReflectionSerializer)
+            if (!JsonSerializerOptions.IsInitializedForReflectionSerializer)
             {
-                options.InitializeForReflectionSerializer();
+                JsonSerializerOptions.InitializeForReflectionSerializer();
             }
 
             return CreateAsyncEnumerableDeserializer(utf8Json, options, cancellationToken);

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

@@ -0,0 +1,327 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.Collections.Concurrent;
+using System.Collections.Generic;
+using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
+using System.Runtime.CompilerServices;
+using System.Text.Json.Serialization;
+using System.Text.Json.Serialization.Metadata;
+
+namespace System.Text.Json
+{
+    public sealed partial class JsonSerializerOptions
+    {
+        /// <summary>
+        /// Encapsulates all cached metadata referenced by the current <see cref="JsonSerializerOptions" /> instance.
+        /// Context can be shared across multiple equivalent options instances.
+        /// </summary>
+        private CachingContext? _cachingContext;
+
+        // Simple LRU cache for the public (de)serialize entry points that avoid some lookups in _cachingContext.
+        // Although this may be written by multiple threads, 'volatile' was not added since any local affinity is fine.
+        private JsonTypeInfo? _lastTypeInfo;
+
+        internal JsonTypeInfo GetOrAddJsonTypeInfo(Type type)
+        {
+            if (_cachingContext == null)
+            {
+                InitializeCachingContext();
+                Debug.Assert(_cachingContext != null);
+            }
+
+            return _cachingContext.GetOrAddJsonTypeInfo(type);
+        }
+
+        internal bool TryGetJsonTypeInfo(Type type, [NotNullWhen(true)] out JsonTypeInfo? typeInfo)
+        {
+            if (_cachingContext == null)
+            {
+                typeInfo = null;
+                return false;
+            }
+
+            return _cachingContext.TryGetJsonTypeInfo(type, out typeInfo);
+        }
+
+        internal bool IsJsonTypeInfoCached(Type type) => _cachingContext?.IsJsonTypeInfoCached(type) == true;
+
+        /// <summary>
+        /// Return the TypeInfo for root API calls.
+        /// This has an LRU cache that is intended only for public API calls that specify the root type.
+        /// </summary>
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        internal JsonTypeInfo GetOrAddJsonTypeInfoForRootType(Type type)
+        {
+            JsonTypeInfo? jsonTypeInfo = _lastTypeInfo;
+
+            if (jsonTypeInfo?.Type != type)
+            {
+                jsonTypeInfo = GetOrAddJsonTypeInfo(type);
+                _lastTypeInfo = jsonTypeInfo;
+            }
+
+            return jsonTypeInfo;
+        }
+
+        internal void ClearCaches()
+        {
+            _cachingContext?.Clear();
+            _lastTypeInfo = null;
+        }
+
+        private void InitializeCachingContext()
+        {
+            _cachingContext = TrackedCachingContexts.GetOrCreate(this);
+        }
+
+        /// <summary>
+        /// Stores and manages all reflection caches for one or more <see cref="JsonSerializerOptions"/> instances.
+        /// NB the type encapsulates the original options instance and only consults that one when building new types;
+        /// this is to prevent multiple options instances from leaking into the object graphs of converters which
+        /// could break user invariants.
+        /// </summary>
+        private sealed class CachingContext
+        {
+            private readonly ConcurrentDictionary<Type, JsonConverter> _converterCache = new();
+            private readonly ConcurrentDictionary<Type, JsonTypeInfo> _jsonTypeInfoCache = new();
+
+            public CachingContext(JsonSerializerOptions options)
+            {
+                Options = options;
+                _ = Count;
+            }
+
+            public JsonSerializerOptions Options { get; }
+            public int Count => _converterCache.Count + _jsonTypeInfoCache.Count;
+            public JsonConverter GetOrAddConverter(Type type) => _converterCache.GetOrAdd(type, Options.GetConverterFromType);
+            public JsonTypeInfo GetOrAddJsonTypeInfo(Type type) => _jsonTypeInfoCache.GetOrAdd(type, Options.GetJsonTypeInfoFromContextOrCreate);
+            public bool TryGetJsonTypeInfo(Type type, [NotNullWhen(true)] out JsonTypeInfo? typeInfo) => _jsonTypeInfoCache.TryGetValue(type, out typeInfo);
+            public bool IsJsonTypeInfoCached(Type type) => _jsonTypeInfoCache.ContainsKey(type);
+
+            public void Clear()
+            {
+                _converterCache.Clear();
+                _jsonTypeInfoCache.Clear();
+            }
+        }
+
+        /// <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"/>.
+        /// Relevant caching contexts are looked up using the equality comparison defined by <see cref="EqualityComparer"/>.
+        /// </summary>
+        private static class TrackedCachingContexts
+        {
+            private const int MaxTrackedContexts = 64;
+            private static readonly ConcurrentDictionary<JsonSerializerOptions, WeakReference<CachingContext>> s_cache =
+                new(concurrencyLevel: 1, capacity: MaxTrackedContexts, new EqualityComparer());
+
+            private const int EvictionCountHistory = 10;
+            private static Queue<int> s_recentEvictionCounts = new(EvictionCountHistory);
+            private static int s_evictionRunsToSkip;
+
+            public static CachingContext GetOrCreate(JsonSerializerOptions options)
+            {
+                if (s_cache.TryGetValue(options, out WeakReference<CachingContext>? wr) && wr.TryGetTarget(out CachingContext? ctx))
+                {
+                    return ctx;
+                }
+
+                lock (s_cache)
+                {
+                    if (s_cache.TryGetValue(options, out wr))
+                    {
+                        if (!wr.TryGetTarget(out ctx))
+                        {
+                            // Found a dangling weak reference; replenish with a fresh instance.
+                            ctx = new CachingContext(options);
+                            wr.SetTarget(ctx);
+                        }
+
+                        return ctx;
+                    }
+
+                    if (s_cache.Count == MaxTrackedContexts)
+                    {
+                        if (!TryEvictDanglingEntries())
+                        {
+                            // Cache is full; return a fresh instance.
+                            return new CachingContext(options);
+                        }
+                    }
+
+                    Debug.Assert(s_cache.Count < MaxTrackedContexts);
+
+                    // Use a defensive copy of the options instance as key to
+                    // avoid capturing references to any caching contexts.
+                    var key = new JsonSerializerOptions(options) { _context = options._context };
+                    Debug.Assert(key._cachingContext == null);
+
+                    ctx = new CachingContext(options);
+                    bool success = s_cache.TryAdd(key, new(ctx));
+                    Debug.Assert(success);
+
+                    return ctx;
+                }
+            }
+
+            private static bool TryEvictDanglingEntries()
+            {
+                // Worst case scenario, the cache has been saturated with permanent entries.
+                // We want to avoid iterating needlessly through the entire cache every time
+                // a new options instance is created. For this reason we implement a backoff
+                // strategy to average out the cost of eviction across multiple cache initializations.
+                // The backoff count is determined by the eviction rates of the most recent eviction runs.
+
+                if (s_evictionRunsToSkip > 0)
+                {
+                    --s_evictionRunsToSkip;
+                    return false;
+                }
+
+                int currentEvictions = 0;
+                foreach (KeyValuePair<JsonSerializerOptions, WeakReference<CachingContext>> kvp in s_cache)
+                {
+                    if (!kvp.Value.TryGetTarget(out _))
+                    {
+                        bool result = s_cache.TryRemove(kvp.Key, out _);
+                        Debug.Assert(result);
+                        currentEvictions++;
+                    }
+                }
+
+                s_evictionRunsToSkip = EstimateEvictionRunsToSkip(currentEvictions);
+                return currentEvictions > 0;
+
+                // Estimate the number of eviction runs to skip based on recent eviction rates.
+                static int EstimateEvictionRunsToSkip(int latestEvictionCount)
+                {
+                    if (s_recentEvictionCounts.Count < EvictionCountHistory)
+                    {
+                        // Insufficient data to determine a skip count.
+                        s_recentEvictionCounts.Enqueue(latestEvictionCount);
+                        return 0;
+                    }
+                    else
+                    {
+                        s_recentEvictionCounts.Dequeue();
+                        s_recentEvictionCounts.Enqueue(latestEvictionCount);
+
+                        // Calculate the average evictions per run.
+                        double avgEvictionsPerRun = 0;
+
+                        foreach (int rate in s_recentEvictionCounts)
+                        {
+                            avgEvictionsPerRun += rate;
+                        }
+
+                        avgEvictionsPerRun /= EvictionCountHistory;
+
+                        // - If avgEvictionsPerRun >= 1 we skip no subsequent eviction calls.
+                        // - If avgEvictionsPerRun < 1 we skip ~ `1 / avgEvictionsPerRun` calls.
+                        int runsPerEviction = (int)Math.Round(1 / Math.Min(Math.Max(avgEvictionsPerRun, 0.1), 1));
+                        Debug.Assert(runsPerEviction >= 1 && runsPerEviction <= 10);
+                        return runsPerEviction - 1;
+                    }
+                }
+            }
+        }
+
+        /// <summary>
+        /// Provides a conservative equality comparison for JsonSerializerOptions instances.
+        /// If two instances are equivalent, they should generate identical metadata caches;
+        /// the converse however does not necessarily hold.
+        /// </summary>
+        private class EqualityComparer : IEqualityComparer<JsonSerializerOptions>
+        {
+            public bool Equals(JsonSerializerOptions? left, JsonSerializerOptions? right)
+            {
+                Debug.Assert(left != null && right != null);
+                return
+                    left._dictionaryKeyPolicy == right._dictionaryKeyPolicy &&
+                    left._jsonPropertyNamingPolicy == right._jsonPropertyNamingPolicy &&
+                    left._readCommentHandling == right._readCommentHandling &&
+                    left._referenceHandler == right._referenceHandler &&
+                    left._encoder == right._encoder &&
+                    left._defaultIgnoreCondition == right._defaultIgnoreCondition &&
+                    left._numberHandling == right._numberHandling &&
+                    left._unknownTypeHandling == right._unknownTypeHandling &&
+                    left._defaultBufferSize == right._defaultBufferSize &&
+                    left._maxDepth == right._maxDepth &&
+                    left._allowTrailingCommas == right._allowTrailingCommas &&
+                    left._ignoreNullValues == right._ignoreNullValues &&
+                    left._ignoreReadOnlyProperties == right._ignoreReadOnlyProperties &&
+                    left._ignoreReadonlyFields == right._ignoreReadonlyFields &&
+                    left._includeFields == right._includeFields &&
+                    left._propertyNameCaseInsensitive == right._propertyNameCaseInsensitive &&
+                    left._writeIndented == right._writeIndented &&
+                    left._context == right._context &&
+                    CompareConverters(left.Converters, right.Converters);
+
+                static bool CompareConverters(IList<JsonConverter> left, IList<JsonConverter> right)
+                {
+                    int n;
+                    if ((n = left.Count) != right.Count)
+                    {
+                        return false;
+                    }
+
+                    for (int i = 0; i < n; i++)
+                    {
+                        if (left[i] != right[i])
+                        {
+                            return false;
+                        }
+                    }
+
+                    return true;
+                }
+            }
+
+            public int GetHashCode(JsonSerializerOptions options)
+            {
+                HashCode hc = default;
+
+                hc.Add(options._dictionaryKeyPolicy);
+                hc.Add(options._jsonPropertyNamingPolicy);
+                hc.Add(options._readCommentHandling);
+                hc.Add(options._referenceHandler);
+                hc.Add(options._encoder);
+                hc.Add(options._defaultIgnoreCondition);
+                hc.Add(options._numberHandling);
+                hc.Add(options._unknownTypeHandling);
+                hc.Add(options._defaultBufferSize);
+                hc.Add(options._maxDepth);
+                hc.Add(options._allowTrailingCommas);
+                hc.Add(options._ignoreNullValues);
+                hc.Add(options._ignoreReadOnlyProperties);
+                hc.Add(options._ignoreReadonlyFields);
+                hc.Add(options._includeFields);
+                hc.Add(options._propertyNameCaseInsensitive);
+                hc.Add(options._writeIndented);
+                hc.Add(options._context);
+
+                foreach (JsonConverter converter in options.Converters)
+                {
+                    hc.Add(converter);
+                }
+
+                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
+        }
+    }
+}