while loop during awaiting for async task

Question

I have a following problem. I have a synchronous .Save() action that takes quite a few minutes to complete. I cannot make it async (3rd party library), so to keep the UI responsive, I am using it all in Task.Run().

I would like to report progress so that the users sees that something is happening - and I want to make it in the Status label - a simple and old school append and remove dots to string, sort of like
Wait.
Wait..
Wait...
Wait.

I don't know how to do it in a simple way - I thought of a while loop that would break once the Task ends, but it doesn't seem to work - either the UI is blocked or the status label does not update.

I tried a couple of things, for example:

bool done = false;
            Task.Run(() =>
            {
                Exporter.DoLongSyncTask();
            }).ContinueWith(r => done = true);
            StatusLabel = ".";
            while (!done)
            {
                if (StatusLabel == "")
                    StatusLabel = ".";
                else if (StatusLabel == ".")
                    StatusLabel = "..";
                else if (StatusLabel == "..")
                    StatusLabel = "";
            }

(StatusLabel is a property with INotifyPropertyChanged implemented, it works OK)

and more complicated

private async Task<bool> DoTheWork()
        {

            await Task.Run(() => TheFile.Save());
            return true;
        }

            private string ReportProgress(string status)
        {
            if (status == ".")
                status = "..";
            else if (status == "..")
                status = "...";
            else if (status == "...")
                status = ".";
            MyProgress.Report(new InDesignExporterProgress { StatusInfo = status });
            return status;
        }

private string ReportProgress(string status)
{
    if (status == ".")
        status = "..";
    else if (status == "..")
        status = "...";
    else if (status == "...")
        status = ".";
    MyProgress.Report(new SomeProgressClass { StatusInfo = status });
    return status;
}

and the above are called from here

        bool done = false;
        Task.Run(() =>
        {
            done = DoTheWork().Result;
        });
        string status = ".";
        while (!done)
        {
            status = ReportProgress(status);
        }

So, what's the right way?

You need to give your UI thread time to do its message pumping. If you can't modify the original method to report progress, one option is to update status periodically based on a timer. — Dan Bryant
– Dan Bryant, Commented Nov 30, 2015 at 23:10
done variable that you can are using to signal two threads might not work because some time value is not immediately available to other thread. — D J
– D J, Commented Nov 30, 2015 at 23:30
@Eser - yes, you're probably right. I read a bit about this and I think I generally understand the concept, can you please point me to an article that could help with this issue? — Bartosz
– Bartosz, Commented Nov 30, 2015 at 23:36
Don't use that done variable, save the task that was created and use task.IsCompleted — Scott Chamberlain
– Scott Chamberlain, Commented Feb 3, 2017 at 20:13

Paulo Morgado · Accepted Answer · 2015-12-01 09:25:17Z

4

To know if a task has been completed, check the value of the IsCompleted property.

while (!task.IsCompleted)
{
    // ...
}

But, for what I think you're trying to, I'd do something like this:

using (var timer = new System.Windows.Forms.Timer())
{
    timer.Tick += (s, e) =>
    {
        if (StatusLabel == "")
            StatusLabel = ".";
        else if (StatusLabel == ".")
            StatusLabel = "..";
        else if (StatusLabel == "..")
            StatusLabel = "";
    };
    timer.Interval = 100;
    timer.Enabled = true;

    await Task.Run(() => Exporter.DoLongSyncTask);
}

answered Dec 1, 2015 at 9:25

Paulo Morgado

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Comments

Cyrus · Accepted Answer · 2017-03-16 15:12:17Z

0

I think you are blocking your UI thread with the while loop since I guess it's running on that thread.

I suggest you try to change your while loop like this and the method signature to async Task

public async Task DoSomething(){
        bool done = false;
        Task.Run(() =>
        {
            Exporter.DoLongSyncTask();
        }).ContinueWith(r => done = true);

        StatusLabel = ".";
        while (!done)
        {
            if (StatusLabel == "")
                StatusLabel = ".";
            else if (StatusLabel == ".")
                StatusLabel = "..";
            else if (StatusLabel == "..")
                StatusLabel = "";
            await Task.Delay(200);
        }
}

edited Mar 16, 2017 at 15:12

answered Nov 30, 2015 at 23:17

Cyrus

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1 Comment

Yacoub Massad Over a year ago

@Eser, can you please explain? what would be a better approach in this case?

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