runtime: System.Text.Json Access Violation Exception (Attempted to read or write protected memory)

Description

First just a quick bit of background: as I’ve raised in comments in #36621, I’ve hit a variety of InvalidProgramException and AccessViolationException while trying to bring System.Text.Json (Previews 4 through 7) to Schema.NET (https://github.com/RehanSaeed/Schema.NET/pull/100). Prior to trying System.Text.Json v5 previews, I had tried v4 which worked with my converter without this exception (though I really wanted the setting to not serialize default values which is coming in v5).

Jumping to now with Preview 7, I’m hitting issues with an AccessViolationException with the error message:

Attempted to read or write protected memory. This is often an indication that other memory is corrupt.

I’ve created a custom solution with as little code as I reasonably could while still using a custom version of the core from Schema.NET: https://github.com/Turnerj/SchemaNet_SystemTextJson

public class CustomType : Thing, IThing
{
	public override string Type => "CustomType";

	[JsonPropertyName("name")]
	[JsonConverter(typeof(ValuesJsonConverter))]
	public OneOrMany<string> Name { get; set; }

	[JsonPropertyName("uri")]
	[JsonConverter(typeof(ValuesJsonConverter))]
	public Values<string, Uri> Uri { get; set; }
}

class Program
{
	static void Main(string[] args)
	{
		// This is the JSON of the object below
		// {"@context":"https://schema.org","@type":"CustomType","name":"Hello World"}
		var inputObj = new CustomType
		{
			Name = "Hello World"
		};

		var json = SchemaSerializer.SerializeObject(inputObj); // Exception occurs on serialization

		var outputObj = SchemaSerializer.DeserializeObject<CustomType>(json);
	}
}

Things to note:

• OneOrMany and Values are both structs which will serialize to a single item or an array
• Values is special because it can convert to and from any of the generic types specified on it
• ValuesJsonConverter does the guts of the converting. In debugging, the CanConvert method is hit however Write is never actually being called on it.
• The ValuesJsonConverter’s CanConvert is: public override bool CanConvert(Type typeToConvert) => typeof(IValues).IsAssignableFrom(typeToConvert);

Configuration

• .NET Core 3.1
• System.Text.Json 5.0.0-preview.7.20364.11
• Windows 10 Home (10.0.18362 Build 18362)
• I’ve hit this issue in CI builds on this pull request for Ubuntu, Mac and Windows

Regression?

As mentioned, I didn’t have this issue with System.Text.Json v4 (likely the last minor version) though I needed v5 as I needed the “don’t serialize default values” configuration.

Other information

Full Exception

System.AccessViolationException: ‘Attempted to read or write protected memory. This is often an indication that other memory is corrupt.’ at DynamicClass.get_Name(System.Object) at System.Text.Json.JsonPropertyInfo1[[System.__Canon, System.Private.CoreLib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e]].GetMemberAndWriteJson(System.Object, System.Text.Json.WriteStack ByRef, System.Text.Json.Utf8JsonWriter) at System.Text.Json.Serialization.Converters.ObjectDefaultConverter1[[System.__Canon, System.Private.CoreLib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e]].OnTryWrite(System.Text.Json.Utf8JsonWriter, System.__Canon, System.Text.Json.JsonSerializerOptions, System.Text.Json.WriteStack ByRef) at System.Text.Json.Serialization.JsonConverter1[[System.__Canon, System.Private.CoreLib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e]].TryWrite(System.Text.Json.Utf8JsonWriter, System.__Canon ByRef, System.Text.Json.JsonSerializerOptions, System.Text.Json.WriteStack ByRef) at System.Text.Json.Serialization.JsonConverter1[[System.__Canon, System.Private.CoreLib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e]].WriteCore(System.Text.Json.Utf8JsonWriter, System.__Canon ByRef, System.Text.Json.JsonSerializerOptions, System.Text.Json.WriteStack ByRef) at System.Text.Json.Serialization.JsonConverter`1[[System.__Canon, System.Private.CoreLib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e]].WriteCoreAsObject(System.Text.Json.Utf8JsonWriter, System.Object, System.Text.Json.JsonSerializerOptions, System.Text.Json.WriteStack ByRef) at System.Text.Json.JsonSerializer.WriteCore[[System.__Canon, System.Private.CoreLib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e]](System.Text.Json.Serialization.JsonConverter, System.Text.Json.Utf8JsonWriter, System.__Canon ByRef, System.Text.Json.JsonSerializerOptions, System.Text.Json.WriteStack ByRef) at System.Text.Json.JsonSerializer.WriteCore[[System.__Canon, System.Private.CoreLib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e]](System.Text.Json.Utf8JsonWriter, System.__Canon ByRef, System.Type, System.Text.Json.JsonSerializerOptions) at System.Text.Json.JsonSerializer.Serialize[[System.__Canon, System.Private.CoreLib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e]](System.__Canon ByRef, System.Type, System.Text.Json.JsonSerializerOptions) at System.Text.Json.JsonSerializer.Serialize[[System.__Canon, System.Private.CoreLib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e]](System.__Canon, System.Text.Json.JsonSerializerOptions) at Schema.NET.SchemaSerializer.SerializeObject(System.Object, System.Text.Json.JsonSerializerOptions) at Schema.NET.SchemaSerializer.SerializeObject(System.Object) at SchemaNet_SystemTextJson.Program.Main(System.String[])

Additionally, when I first went to Preview 4, while I didn’t hit this exception, I did hit a CLR exception (“Common Language Runtime detected an invalid program”).

While this issue is happening with serialization, I have experienced similar issues with deserialization too when running CI builds of the Schema.NET PR I’ve linked to a few times. I’m thinking the fix for serialization might fix the deserialization issue too.