CODEWITHSUNDEEP
c#multithreadinguser-interfacefreeze
NESHOM
NESHOM

Reputation: 929

Thread running a heavy method is slowing down the UI in C#

Does anyone know why this code is slowing down the UI:

Thread trdGenerateTrajectory = new Thread(() => HeavyMethod());
trdGenerateTrajectory.Start();
trdGenerateTrajectory.Join();

This is supposed to be in a separate thread than the main thread, am I right? If so, why running it slows down/freezes the UL?

EDIT: Thanks for your comments. I removed Join(), but it still freezes the UI. Any idea?

UPDATE: The HeavyMethod() method is calling a method from a Matlab dll that I created. The method in the dll generates manipulation trajectory for a robot. My project is a heavy robotics project that communicates with lots of hardware/devices. The project has 12 backgroundworkers and one timer. The timer is responsible for updating the UI and all of the texts/colors/images/... on it. I haven't had any issue so far with the backgroundworkers and the timer and no matter how heavy were the tasks they are runing, I never saw any delay or stop on the timer and UI update. However, when I call this specific method in Matlab dll, I see a full stop on UI being updated until the method is completed. This is what I experienced:

  1. I used threads (above code) with no luck.
  2. I then moved the method and the process after running method into another backgroundworker, again with no luck.

Then I realized that just some of the textboxes on my form are experiencing this issue. They are those that are getting their values from another method of the same Matlab dll. That was the time that I realized that this issue has nothing to do with threads/backgroundworkers and is related to the Matlab way of running methods. Maybe it is single threaded!? Anyway, I though it may help if I make separate dll for this specific method that generates trajectory, so I created another dll, but I experienced the exact same issue. It seems like Matlab dll can only run one method at a time no matter if you call them from different threads or even from separate dll. I believe I should ask this in separate SO question and I will, but, in the meantime, do you have any comment on this? (Update: I didn't receive any reply so I posted a new question: Calling two functions from a single Matlab dll at the same time)

Upvotes: 0

Views: 2499

Answers (2)

Douglas
Douglas

Reputation: 54897

Although you're running your computation on a background thread, your Join call causes your UI thread to block anyway until your computation completes.

The proper way to do this today would be using the async and await keywords. If you really want to restrict yourself to threads, you can use an Invoke call within the thread to dispatch control back to the UI thread once the computation completes:

Thread trdGenerateTrajectory = new Thread(() => 
{
    HeavyMethod();

    this.Invoke(new Action(() =>
    {
         // Update UI here.
    }));
});

trdGenerateTrajectory.Start();
// trdGenerateTrajectory.Join(); <- do not block

Edit: Assuming that you want to run your computation in response to some button click (or any other event), you can use the async pattern in the event handler like so:

private async void myButton_Click()
{
    await Task.Run(HeavyMethod);

    // Update UI here.
}

Upvotes: 6

Boris Bera
Boris Bera

Reputation: 898

You're starting the thread and immediately joining it. Joining the thread means that you are waiting for it to end.

Normally, user interfaces are single threaded. This means that your method needs to return for another event to be processed.

Upvotes: 4

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