Как синхронизировать доступ к Списку <T> используемый в ASP.NET?

Вот как я это сделаю в APi

public ActionResult SomeActionMethod() {
  return Json(new {foo="bar", baz="Blech"});
}

Если вы хотите использовать JsonConverter и контролировать, как данные сериализуются, то

  public class JsonNetResult : ActionResult
    {
        /// <summary>
        /// Initializes a new instance of the <see cref="JsonNetResult"/> class.
        /// </summary>
        public JsonNetResult()
        {
        }

        /// <summary>
        /// Gets or sets the content encoding.
        /// </summary>
        /// <value>The content encoding.</value>
        public Encoding ContentEncoding { get; set; }

        /// <summary>
        /// Gets or sets the type of the content.
        /// </summary>
        /// <value>The type of the content.</value>
        public string ContentType { get; set; }

        /// <summary>
        /// Gets or sets the data.
        /// </summary>
        /// <value>The data object.</value>
        public object Data { get; set; }


        /// <summary>
        /// Enables processing of the result of an action method by a custom type that inherits from the <see cref="T:System.Web.Mvc.ActionResult"/> class.
        /// </summary>
        /// <param name="context">The context in which the result is executed. The context information includes the controller, HTTP content, request context, and route data.</param>
        public override void ExecuteResult(ControllerContext context)
        {
            if (context == null)
            {
                throw new ArgumentNullException("context");
            }

            HttpResponseBase response = context.HttpContext.Response;

            response.ContentType = !String.IsNullOrWhiteSpace(this.ContentType) ? this.ContentType : "application/json";

            if (this.ContentEncoding != null)
            {
                response.ContentEncoding = this.ContentEncoding;
            }


            if (this.Data != null)
            {

                response.Write(JsonConvert.SerializeObject(this.Data));

            }
        }
    }

Blockquote [117 ]

    public class CallbackJsonResult : JsonNetResult
    {
        /// <summary>
        /// Initializes a new instance of the <see cref="CallbackJsonResult"/> class.
        /// </summary>
        /// <param name="statusCode">The status code.</param>
        public CallbackJsonResult(HttpStatusCode statusCode)
        {
            this.Initialize(statusCode, null, null);
        }

        /// <summary>
        /// Initializes a new instance of the <see cref="CallbackJsonResult"/> class.
        /// </summary>
        /// <param name="statusCode">The status code.</param>
        /// <param name="description">The description.</param>
        public CallbackJsonResult(HttpStatusCode statusCode, string description)
        {
            this.Initialize(statusCode, description, null);
        }

        /// <summary>
        /// Initializes a new instance of the <see cref="CallbackJsonResult"/> class.
        /// </summary>
        /// <param name="statusCode">The status code.</param>
        /// <param name="data">The callback result data.</param>
        public CallbackJsonResult(object data, HttpStatusCode statusCode = HttpStatusCode.OK)
        {
            this.ContentType = null;
            this.Initialize(statusCode, null, data);
        }



        /// <summary>
        /// Initializes a new instance of the <see cref="CallbackJsonResult"/> class.
        /// </summary>
        /// <param name="statusCode">The status code.</param>
        /// <param name="description">The description.</param>
        /// <param name="data">The callback result data.</param>
        public CallbackJsonResult(HttpStatusCode statusCode, string description, object data)
        {
            this.Initialize(statusCode, description, data);
        }

        /// <summary>
        /// Initializes this instance.
        /// </summary>
        /// <param name="statusCode">The status code.</param>
        /// <param name="description">The description.</param>
        /// <param name="data">The callback result data.</param>
        private void Initialize(HttpStatusCode statusCode, string description, object data)
        {
            Data = new JsonData() { Success = statusCode == HttpStatusCode.OK, Status = (int)statusCode, Description = description, Data = data };
        }
    }
}

затем создайте расширение

/// <summary>
/// return Json Action Result
/// </summary>
/// <typeparam name="T"></typeparam>
/// <param name="o"></param>
/// <param name="JsonFormatting"></param>
/// <returns></returns>
public static CallbackJsonResult ViewResult<T>(this T o)
{
    return new CallbackJsonResult(o);
}

Нет APi, просто используйте созданное вами расширение

public ActionResult SomeActionMethod() {
  return new { error = "", code = (int)HttpStatusCode.OK, data = leads}.ViewResult();
}