How do I make this method async?

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Inside my SchedulerService WCF service, I have a method as follows:

public void Process(bool isForced)
{
    var prevStatus = Status;
    Status = SchedulerStatus.Processing;
    ProcessListings();
    Status = prevStatus;
}

Now I have a view model that polls the Status property, and all is good except with the above method. ProcessListings is long-running, and it blocks the thread so that my status poll calls are blocked until ProcessListings returns. This is problematic, as I need to know if the status is "Processing" after calling Process, and I need to continue polling the status while ProcessListings is running.

How can I use the new asynchrony features, or older ThreadPool features, to execute ProcessListings without blocking calls to other methods in SchedulerService? The polling is an essential workaround as I do not have any more time to try and get WCF callbacks working into a WPF project.

Posted 3-Mar-15 22:56pm

Brady Kelly

Updated 3-Mar-15 22:57pm

v3

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2 solutions

Solution 2

I have accepted Richard's solution, because it answered the question well, but I'm just posting mine here to show exactly how I achieved what was needed.

Making ProcessListings was as simple as:

C#

private static Task ProcessListings()
{
    return Task.Run(() => Thread.Sleep(5000));            
}

And then calling it as simple as:

C#

public async void Process(bool isForced)
{
    var prevStatus = Status;
    Status = SchedulerStatus.Processing;
    await ProcessListings();
    Status = prevStatus;
}

Posted 4-Mar-15 2:22am

Brady Kelly

Comments

Richard Deeming 4-Mar-15 8:27am

I assume that's a simplified version of the ProcessListings method? You'd do better to use:

private static Task ProcessListings()
{
    return Task.Delay(5000);
}

Brady Kelly 4-Mar-15 8:30am

Oooh, thanks. Yes, my version just kludges in a delay so I can read the status when it changes in the UI.

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Richard Deeming · Accepted Answer · 2015-03-04T01:24:00

Solution 1

If you can change the ProcessListings method to do its work asynchronously, and return a Task, then this would be simple:

C#

public async Task ProcessAsync(bool isForced)
{
    var prevStatus = Status;
    Status = SchedulerStatus.Processing;
    await ProcessListingsAsync();
    Status = prevStatus;
}

If you can't change the ProcessListings method, then you'll need to run the method on a background thread - the simplest option would be to use Task.Run[^]:

C#

public async Task ProcessAsync(bool isForced)
{
    var prevStatus = Status;
    Status = SchedulerStatus.Processing;
    await Task.Run(ProcessListings);
    Status = prevStatus;
}

Posted 4-Mar-15 1:24am

Richard Deeming

Comments

Brady Kelly 4-Mar-15 8:17am

Thanks Richard. I already figured it out, and feel stupid it's so simple, but I'm up to my ears getting other stuff to work by yesterday, so I never tried anything myself yet. What your answer is short on, and sort of what I was looking for, is how to make ProcessListings async, returning a Task. I'll post my solution just to illustrate my code, but your's is accepted.

Richard Deeming 4-Mar-15 8:18am

Which is impossible to answer without seeing what ProcessListings is doing. :)

Brady Kelly 4-Mar-15 8:26am

It actually calls one service to pull data from a WCF web service into the DB, then calls another service to pull data from the DB and push it to a good ol' SOAPy web service. Can you believe people are still using that old tech for brand new systems?

Richard Deeming 4-Mar-15 8:39am

When you import the service, there's an option to "Generate Asynchronous Operations" hidden under the "Advanced" button.

That will generate traditional APM signatures (Begin... / End... using IAsyncResult). You can then use the Task.Factory.FromAsync method[^] to turn those methods into a Task<T>, which you can use from your async method. (You should chose an overload that takes a beginMethod rather than an IAsyncResult, as Stephen Toub explains[^].)

Brady Kelly 4-Mar-15 8:45am

Cool, thanks again. The service methods I'm calling in ProcessListings are plain old POCO methods, not MVC, so I can't generate async operations for them. Next version maybe, but everything here is so long running, I feel much safer only having one async method doing all the work synchronously.

Richard Deeming 4-Mar-15 8:48am

It doesn't matter what the back-end of the service is; you can still generate asynchronous methods in the client. :)

Brady Kelly 4-Mar-15 8:57am

How? I'm not adding a service reference or anything. I'm just referencing a plain C# library and calling its methods. There is no generator that I can see.

Richard Deeming 4-Mar-15 9:00am

Ah, OK. When you said "pull data from a WCF service", I thought you meant you were calling a WCF service. :P

Brady Kelly 4-Mar-15 9:35am

Oh, sorry, my mistake. That, the source, is an attempt at a REST service - call a URL and get XML back, and the destination is an old fashioned web service. There is only my WCF. What was I thinking, that either of these two new businesses would dare use WCF. They do both use .NET, so no excuse.

Richard Deeming 4-Mar-15 9:39am

How are you calling the URL? Both the WebClient class[^] and the new HttpClient class[^] provide task-based async methods.

Brady Kelly 4-Mar-15 10:11am

WebClient, but I really have nothing else to do while waiting for it :-) This is all a permanently running background service, with a tiny little control panel to start and stop it and view its log. When I start integrating with multiple destinations, this POC code will get overhauled.

Richard Deeming 4-Mar-15 10:14am

I'd still be inclined to use the async methods. That way, you're not eating CPU cycles waiting for the request to complete.

Other processes running on the computer will thank you. :)

Brady Kelly 4-Mar-15 13:08pm

My client will first thank me for it just working, even if it eats all the GHz, but once he's testing, I will have time to review the current modus operandi. And I'll have some pay.