[may be a bug] serilize Task object will let cpu 100%

[fawdlstty]

Issue Title

serilize Task object will let cpu 100%

General

IDE: VS2019 Community
Version: .net core 3.1
System: both Win10 and Centos 7.5
Framework: ASP.Net Core

public IActionResult test () {
    var content = Task.Run (...);// Task object
    return new OkObjectResult (new { result = true, reason = "", content });
}

if I use Newtonsoft.Json to serilize the object, it will throw a exception, but if I use the code, It will always lock with there and let CPU 100%

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[scalablecory]

Not sure if it should go to JSON or ASP.NET. CC @Pilchie

[Pilchie]

Pretty sure it's just JSON, but maybe @pranavkm can confirm that it's not something ASP.NET is doing.

[pranavkm]

We don't do anything interesting during serialization that would cause this. That said, you're attempting to serialize a Task that returns a value i.e. a Task<T>, the serializer is going to synchronously block evaluating the Result property. I can't think of any good reason you would want to serialize a Task \ ValueTask instance, it most likely indicates a programming error. Perhaps the serializer could add a custom converter that throws anytime it encounters one of these? That way it throws by default and you get a useful error and users have a way to opt out if they relied on the serialized format.

[fawdlstty]

The serializer does not wait for Result, because the asynchronous method completes quickly, but the serializer stays blocked

[layomia]

We can add a converter factory to throw when one of these types is encountered, similar to the work done in #34249.

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