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Cache polymorphic properties #41753

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Oct 21, 2019
Merged

Cache polymorphic properties #41753

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5d363fa
Cache polymorphic properties
svick Oct 13, 2019
92b9b1e
Move RuntimePropertyCache to JsonClassInfo
svick Oct 17, 2019
2f0cf17
Added test of RuntimePropertyCache using properties with different at…
svick Oct 17, 2019
826bc61
Fixed typo
svick Oct 17, 2019
df45181
Use allocating overload of GetOrAdd on .Net Standard 2.0
svick Oct 18, 2019
e72ba56
Merge branch 'master' into json-object-property
svick Oct 21, 2019
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31 changes: 20 additions & 11 deletions src/System.Text.Json/src/System/Text/Json/Serialization/JsonClassInfo.AddProperty.cs
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Expand Up @@ -2,10 +2,11 @@
// The .NET Foundation licenses this file to you under the MIT license.
// See the LICENSE file in the project root for more information.

using System.Collections.Generic;
using System.Collections.Concurrent;
using System.Diagnostics;
using System.Reflection;
using System.Text.Json.Serialization;
using System.Threading;

namespace System.Text.Json
{
Expand Down Expand Up @@ -209,18 +210,26 @@ internal JsonPropertyInfo CreateRootObject(JsonSerializerOptions options)
options: options);
}

internal JsonPropertyInfo CreatePolymorphicProperty(JsonPropertyInfo property, Type runtimePropertyType, JsonSerializerOptions options)
internal JsonPropertyInfo GetOrAddPolymorphicProperty(JsonPropertyInfo property, Type runtimePropertyType, JsonSerializerOptions options)
{
JsonPropertyInfo runtimeProperty = CreateProperty(
property.DeclaredPropertyType, runtimePropertyType,
property.ImplementedPropertyType,
property.PropertyInfo,
parentClassType: Type,
converter: null,
options: options);
property.CopyRuntimeSettingsTo(runtimeProperty);
static JsonPropertyInfo CreateRuntimeProperty(Type runtimePropertyType, (JsonPropertyInfo property, JsonSerializerOptions options, Type classType) arg)
{
JsonPropertyInfo runtimeProperty = CreateProperty(
arg.property.DeclaredPropertyType, runtimePropertyType,
arg.property.ImplementedPropertyType,
arg.property.PropertyInfo,
parentClassType: arg.classType,
converter: null,
options: arg.options);

arg.property.CopyRuntimeSettingsTo(runtimeProperty);

return runtimeProperty;
}

var cache = LazyInitializer.EnsureInitialized(ref property.RuntimePropertyCache, () => new ConcurrentDictionary<Type, JsonPropertyInfo>());
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nit: Don't use var here.

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Is this preferred over Lazy<T>?

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@svick svick Oct 15, 2019 •
edited
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I think it's preferred here, since Lazy<T> would require an allocation of an instance of Lazy<T> for every instance of JsonPropertyInfo (even if it didn't have any polymorphic properties).

But that's a moot point anyway if we're going to reuse JsonClassInfo.PropertyCache (more on that later).


return runtimeProperty;
return cache.GetOrAdd(runtimePropertyType, (type, arg) => CreateRuntimeProperty(type, arg), (property, options, Type));
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@ahsonkhan ahsonkhan Oct 14, 2019 •
edited
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@steveharter, unrelated to this PR, but here is some code cleanup we should consider (separately - out of scope for this PR which we should keep focused on the perf fix only):
Using Type as a property name makes code like this quite hard to parse/reason about. I was confused where Type is coming from and how we were passing in System.Type (i.e. a type) as a method parameter.

corefx/src/System.Text.Json/src/System/Text/Json/Serialization/JsonClassInfo.cs

Line 77 in 437d9bc

public Type Type { get; private set; }

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@steveharter steveharter Oct 15, 2019 •
edited
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Is "ClassType" better? (somewhat redundant) Or just doc? The actual type can be a POCO type or any property type (string, List<string>, etc).

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We already have a ClassType property, so that wouldn't work.

corefx/src/System.Text.Json/src/System/Text/Json/Serialization/JsonClassInfo.cs

Line 42 in 437d9bc

public ClassType ClassType { get; private set; }

}
}
}
3 changes: 3 additions & 0 deletions src/System.Text.Json/src/System/Text/Json/Serialization/JsonPropertyInfo.cs
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Expand Up @@ -3,6 +3,7 @@
// See the LICENSE file in the project root for more information.

using System.Collections;
using System.Collections.Concurrent;
using System.Diagnostics;
using System.Reflection;
using System.Text.Json.Serialization;
Expand Down Expand Up @@ -584,5 +585,7 @@ private void VerifyWrite(int originalDepth, Utf8JsonWriter writer)
ThrowHelper.ThrowJsonException_SerializationConverterWrite(ConverterBase);
}
}

public ConcurrentDictionary<Type, JsonPropertyInfo> RuntimePropertyCache;
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Should this be stored on the JsonSerializerOptions instead with the rest of the caches?

Also, can the following existing cache be used for the runtime properties as well?

corefx/src/System.Text.Json/src/System/Text/Json/Serialization/JsonSerializerOptions.cs

Line 23 in 437d9bc

private readonly ConcurrentDictionary<Type, JsonPropertyInfo> _objectJsonProperties = new ConcurrentDictionary<Type, JsonPropertyInfo>();

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On _objectJsonProperties I believe @layomia is working to get rid of that cache.

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Should this be stored on the JsonSerializerOptions instead with the rest of the caches?

By storing the cache on the actual JsonPropertyInfo like it is currently means we are tied to a particular class + particular property that may have specific attribute (e.g. [JsonIgnore] and [JsonConverter] which we need to preserve.

If we store the cache on a JsonSerializerOptions instance then we would would need to key on class type + property name + property type.

If we store the cache on a JsonClassInfo instance then we would need to key on property name + property type.

The cache in the current location of a JsonPropertyInfo instance is the most specific, but that also means we are instantiating a new dictionary for every polymorphic property, which probably isn't ideal, especially in the future when we likely support polymorphic properties in cases other than System.Object.

So I think storing on JsonClassInfo is the best location like we have for the current property cache already there: public volatile Dictionary<string, JsonPropertyInfo> PropertyCache. However, we should be able to just use the existing cache by changing the "string" key to be property name + property type (just for polymorphic properties) then we can just re-use the existing cache.

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@steveharter

we should be able to just use the existing cache

I don't think that would be a good idea, since it would require allocating a string for every access to serve as the key. So you're likely paying lots of string allocations to avoid a single dictionary allocation.

Just moving the cache to JsonClassInfo (while using a (name, type) tuple as the key) sounds reasonable to me.

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@svick yes allocating a string for the key is not ideal, but small overhead compared to what we have today. A dictionary is heavy-weight so having one instance for a Type is much better than per property.

However creating a new cache on JsonClassInfo with the propertyName+propertyType tuple as you suggest would be OK, but JsonPropertyInfo+propertyType might be a bit more performant and works because the same JsonPropertyInfo coming in is (should) be the same instance each time.

}
}
2 changes: 1 addition & 1 deletion src/System.Text.Json/src/System/Text/Json/Serialization/JsonSerializer.Read.HandleArray.cs
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Expand Up @@ -31,7 +31,7 @@ public static partial class JsonSerializer
}
else if (state.Current.JsonClassInfo.ClassType == ClassType.Unknown)
{
jsonPropertyInfo = state.Current.JsonClassInfo.CreatePolymorphicProperty(jsonPropertyInfo, typeof(object), options);
jsonPropertyInfo = state.Current.JsonClassInfo.GetOrAddPolymorphicProperty(jsonPropertyInfo, typeof(object), options);
}

// Verify that we have a valid enumerable.
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2 changes: 1 addition & 1 deletion src/System.Text.Json/src/System/Text/Json/Serialization/JsonSerializer.Read.HandleValue.cs
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Expand Up @@ -24,7 +24,7 @@ private static void HandleValue(JsonTokenType tokenType, JsonSerializerOptions o
}
else if (state.Current.JsonClassInfo.ClassType == ClassType.Unknown)
{
jsonPropertyInfo = state.Current.JsonClassInfo.CreatePolymorphicProperty(jsonPropertyInfo, typeof(object), options);
jsonPropertyInfo = state.Current.JsonClassInfo.GetOrAddPolymorphicProperty(jsonPropertyInfo, typeof(object), options);
}

jsonPropertyInfo.Read(tokenType, ref state, ref reader);
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2 changes: 1 addition & 1 deletion src/System.Text.Json/src/System/Text/Json/Serialization/JsonSerializer.Write.Helpers.cs
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Expand Up @@ -31,7 +31,7 @@ private static void GetRuntimePropertyInfo(object value, JsonClassInfo jsonClass
// Nothing to do for typeof(object)
if (runtimeType != typeof(object))
{
jsonPropertyInfo = jsonClassInfo.CreatePolymorphicProperty(jsonPropertyInfo, runtimeType, options);
jsonPropertyInfo = jsonClassInfo.GetOrAddPolymorphicProperty(jsonPropertyInfo, runtimeType, options);
}
}
}
Expand Down
7 changes: 7 additions & 0 deletions src/System.Text.Json/tests/Serialization/Object.WriteTests.cs
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Expand Up @@ -75,5 +75,12 @@ private class Indexer

public string NonIndexerProp { get; set; }
}

[Fact]
public static void WriteCollectionAsObject()
{
string json = JsonSerializer.Serialize(new { Prop = (object)new[] { 0 } });
Assert.Equal(@"{""Prop"":[0]}", json);
}
}
}
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Please add tests with different properties with the same Type but with different attributes (e.g. [JsonIgnore]) to ensure the cache's key works as expected.