Need Guidance on How to make Function Async/Non Blocking

Question

Suppose I have a HttpHelper class that has a GetResponseStream(), that upload request data showing progress via events StatusChanged & ProgressChanged.

public MemoryStream GetResponseStream() {
    ...
    Status = Statuses.Uploading; // this doesn't raise StatusChanged
    // write to request stream
    ... // as I write to stream, ProgressChanged doesn't get raised too
    Status = Statuses.Downloading; // this too
    // write to response stream
    ... // same here
    Status = Statuses.Idle; // this runs ok. Event triggered, UI updated
}

Code @pastebin. GetRequestStream() on line 76. The class itself works fine except the using class need to call it like below

HttpHelper helper = new HttpHelper("http://localhost/uploadTest.php");
helper.AddFileHeader("test.txt", "test.txt", "text/plain", File.ReadAllBytes("./test.txt"));
helper.StatusChanged += (s, evt) =>
{
    _dispatcher.Invoke(new Action(() => txtStatus.Text = helper.Status.ToString()));

    if (helper.Status == HttpHelper.Statuses.Idle || helper.Status == HttpHelper.Statuses.Error)
        _dispatcher.Invoke(new Action(() => progBar.IsIndeterminate = false));

    if (helper.Status == HttpHelper.Statuses.Error)
        _dispatcher.Invoke(new Action(() => txtStatus.Text = helper.Error.Message));
};
helper.ProgressChanged += (s, evt) =>
{
    if (helper.Progress.HasValue)
        _dispatcher.Invoke(new Action(() => progBar.Value = (double)helper.Progress));
    else
        _dispatcher.Invoke(new Action(() => progBar.IsIndeterminate = true));
};
Task.Factory.StartNew(() => helper.GetResponseString());

If I had called the class using

helper.GetResponseString();

Then the class itself will work, but events don't seem to be raised. I think it has to do with the UI thread being blocked. How can I at recode the class such that its easier/cleaner for the using class to use it, without all the _dispatcher & Task stuff.

Also, I will like to know for sure whats causing the events/UI to not update. Even if the code is synchronous, can't it run the property changed/events anyways, its after the read/write afterall?

You should set the PasteBin syntax highlighting to C#. pastebin.com/FeAPB6rU — SLaks
– SLaks, Commented Nov 23, 2010 at 2:25
@SLaks, Thanks for notifying me on that, must have been doing PHP yest and forgot to change the language — Jiew Meng
– Jiew Meng, Commented Nov 23, 2010 at 3:01

OJ. · Accepted Answer · 2010-11-23 03:54:06Z

2

You should look into using the BackgroundWorker instead of hand-crafting this yourself. Use ReportProgress to pass the state of processing to your UI thread.

answered Nov 23, 2010 at 3:54

OJ.

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1 Comment

Ian Griffiths Over a year ago

While this is probably a good suggestion for this question, I'd like to add a caveat, because there are scenarios in which this might be less good: a problem with this suggestion is that it'll end up consuming a thread for as long as the work is in progress. It's unlikely to be a problem in client-side code (which is what the question seems to be about), but on server-side code it would defeat the point of doing things asynchronously. Full-on async use of networking classes enables far more frugal use of threads, which can sometimes help server scalability. (But would be overengineering here.)

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