使用Task.Run写一个异步方法

Question

I just want a sanity check on this, because I have little experience writing asynchronous functions.

I am subclassing an abstract class and need to override a function with the following signature:

public abstract Task WriteResponseBodyAsync(OutputFormatterWriteContext context);

The function must return task, and my override does not use any asynchronous functions, so to return Task I use Task.Run. Is this the correct usage?

public class FhirJsonFormatter : TextOutputFormatter
{    
    public override Task WriteResponseBodyAsync(OutputFormatterWriteContext context, Encoding selectedEncoding)
    {
        Hl7.Fhir.Serialization.FhirJsonSerializer ser = new Hl7.Fhir.Serialization.FhirJsonSerializer();

        using (System.IO.StreamWriter sw = new System.IO.StreamWriter(context.HttpContext.Response.Body))
        {
            using (Newtonsoft.Json.JsonWriter jw= new Newtonsoft.Json.JsonTextWriter(sw))
            {
                return Task.Run(() => { ser.Serialize((Hl7.Fhir.Model.Base)context.Object, jw); });
            }
        }
    }
}

Answer 1

Task.Run will run the code on another thread, which is probably not what you want.

Why not just return Task.CompletedTask :

public override Task WriteResponseBodyAsync(OutputFormatterWriteContext context, Encoding selectedEncoding)
{
    Hl7.Fhir.Serialization.FhirJsonSerializer ser = new Hl7.Fhir.Serialization.FhirJsonSerializer();

    using (System.IO.StreamWriter sw = new System.IO.StreamWriter(context.HttpContext.Response.Body))
    {
        using (Newtonsoft.Json.JsonWriter jw= new Newtonsoft.Json.JsonTextWriter(sw))
        {
            ser.Serialize((Hl7.Fhir.Model.Base)context.Object, jw);
        }
    }
    return Task.CompletedTask;
}

Also with your example, the method may return before ser.Serialize has finished, causing jw , sw and maybe even context to be disposed.