Execute a javascript function on completion of C# async function

Question

I have a jquery Ajax function

  var arr = {
                id: 1,
                run: true
            }
  $.ajax({
            url: '@Url.Action("Getdata", "Details")',
            data: { Batch: arr},
            type: "POST",
            success: function (result) {
                if (result) {
                    GenNamespace.Completed(result);
                }
            },
            error: function (result) { alert("Problem Occured"); },
        });

which calls c# async function, and on successful completion of the task i am executing some function in jquery ajax success

       public async Task<JsonResult> GetData(Batch arr)
    {
        try
        {
            var success = false;
            var t = await Task.Run(() =>
            {
            //i am Performing long running task here
             return Json(success, JsonRequestBehavior.AllowGet);
            }
            });
            return t;
          }
        catch (Exception ex)
        {
            throw ex;
        }
        return null;
    }

however this is a async function, so the value(success = false) gets returned to the jquery success even though the function is not completely executed, so how do i call the javascript function only upon completion of this task, is there a task completed notification or something which i could use here in this scenario?

Async controller actions are only asynchronous from the point of view of the asp.net thread, they are not asynchronous to the JavaScript client caller. — Coding Flow
– Coding Flow, Commented Sep 10, 2015 at 8:49
@BenRobinson- Yes, that's true, i wanted to know how i could use it for the advantage in this situation, — G--
– G--, Commented Sep 10, 2015 at 8:50
might be a silly question, but do you set success variable to true in Task.Run? — xZ6a33YaYEfmv
– xZ6a33YaYEfmv, Commented Sep 10, 2015 at 8:52
Not sure what you are trying to do, the javscript will not see a difference between and async controller action and a normal one, the reason it returns success false seems to be because you are never setting it to true. — Coding Flow
– Coding Flow, Commented Sep 10, 2015 at 8:54
@ieaglle- Yes, i do set in the last line of the function, but initially it would be false, but it would not wait till the function gets completed, it would start the task and return to success of jqAjax. — G--
– G--, Commented Sep 10, 2015 at 8:56

xZ6a33YaYEfmv · Accepted Answer · 2015-09-10 15:35:37Z

6

The next code works just as expected (and it is almost equal to yours):

    [HttpPost]
    public async Task<JsonResult> GetData()
    {
        var succ = false;
        var taskRes = await Task.Run(async () =>
       {
           await Task.Delay(10000);
           succ = true;
           return Json(succ, JsonRequestBehavior.AllowGet);
       });

        return taskRes;
    }

    $.ajax({
        url: '@Url.Action("GetData", "Home")',
        type: "POST",
        success: function (result) {
            console.log(result);
        },
        error: function (result) { alert("Problem Occured"); },
    });

After execution (10s) there's 'true' in console.

edited Sep 10, 2015 at 15:35

answered Sep 10, 2015 at 9:27

xZ6a33YaYEfmv

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Comments

Devon Burriss · Accepted Answer · 2015-09-10 09:17:37Z

2

How about something like this. I think what is happening for you is that you are calling the async task but the program will continue on and return. Untested...

UPDATE: This blocks and so removes any async benefits.

    public async Task<JsonResult> GetData(Batch arr)
    {
        try
        {
            return DoTask().Result;
        }
        catch (Exception ex)
        {
            throw ex;
        }
        return null;
    }

    private async Task<JsonResult> DoTask()
    {
        var success = false;
        var t = await Task.Run(() =>
        {
            //i am Performing long running task here
            success = true;
            return Json(success, JsonRequestBehavior.AllowGet);
        });
        return t;
    }

If you you wanted true async between the javascript client and your API I suggest you look at SignalR.

edited Sep 10, 2015 at 9:17

answered Sep 10, 2015 at 8:58

Devon Burriss

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6 Comments

G-- Over a year ago

@deebo- thanks for the solution, i would check this and let you know.

xZ6a33YaYEfmv Over a year ago

Result property blocks current thread so there is no point in async here.

G-- Over a year ago

@ieaglle- then i have completely misunderstood the concept, i would then have to read async again!

Devon Burriss Over a year ago

Yes sorry I should have been explicit about that in my answer. That is why I mentioned SignalR.

xZ6a33YaYEfmv Over a year ago

@deebo, SignalR allows duplex communication and it is not required here as I understood.

|

wilw · Accepted Answer · 2023-03-08 03:31:56Z

0

You are not considering the stateless HTTP connection separating the client from the server. If the websocket was kept open, we could do all sorts async behavior like lazy loading of data between the client and server (Without EF). But with IObservable and Promises, there are other ways to accomplish true end-to-end async behavior. IT all comes down to how you slice and dice.

answered Mar 8, 2023 at 3:31

wilw

1

1 Comment

Community Over a year ago

As it’s currently written, your answer is unclear. Please edit to add additional details that will help others understand how this addresses the question asked. You can find more information on how to write good answers in the help center.

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