Thread updating GUI freezes in random moments

Question

I have form with button and text box. Button is starting thread which is updating value of text box.

    public Form1()
    {
        InitializeComponent();
        myDelegate = new UpdateUi(updateUi);
    }
    private void button1_Click(object sender, EventArgs e)
    {
        myThread = new Thread(new ThreadStart(ThreadFunction));
        myThread.Start();
    }
    private void ThreadFunction()
    {
        MyThreadClass myThreadClassObject  = new MyThreadClass(this);
        myThreadClassObject.Run();
    }
    private void updateUi(int i)
    {
        textBox1.Text = i.ToString();
        Thread.Sleep(1000);
    }
    public Thread myThread;
    public delegate void UpdateUi(int i);
    public UpdateUi myDelegate;

and ThreadClass:

public class MyThreadClass
{
    Form1 myFormControl1;
    public MyThreadClass(Form1 myForm)
    {
        myFormControl1 = myForm;
    }

    public void Run()
    {
        // Execute the specified delegate on the thread that owns
        // 'myFormControl1' control's underlying window handle.
        for(int i=0;i<100;i++)
        {
            if(myFormControl1.InvokeRequired)
            {
                myFormControl1.Invoke(myFormControl1.myDelegate,i);
            }

        }


    }
}

As You can see there is nothing special in my code but sometimes the code freeze.

eg it goes 1->2->3->freeze->16->17 and so on.

I took code from HERE with little modifications

The `Thread.Sleep` in the example is only to slow it down. You don't want that, so simply remove it from your code. — Andrew Morton, Sep 22 '14 at 10:54
So You tell me that `Thread.Sleep` is responsible for that strange behavior? — szpic, Sep 22 '14 at 10:59
@szpic [Thread.Sleep Method (Int32)](http://msdn.microsoft.com/en-us/library/d00bd51t%28v=vs.110%29.aspx): "Suspends the current thread for the specified number of milliseconds." If the UI thread is in a sleep state, it is frozen. — Andrew Morton, Sep 22 '14 at 11:02
The sleep should be inside the loop of `MyThreadClass.Run()`, not in the code that is being run on the UI in `updateUi()`. — Matthew Watson, Sep 22 '14 at 11:03
Try putting the `Thread.Sleep(1000);` inside the `Run()` method. — George Chondrompilas, Sep 22 '14 at 11:03
@MatthewWatson I updated question with delegate. And thanks for suggestion of moving the sleep. Now its working properly. But why sometimes Thread.Sleep was causing freeze for 10-15 seconds instead of 1 as is set? — szpic, Sep 22 '14 at 11:06

score 1 · Accepted Answer · answered Sep 22 '14 at 11:16

The issue is you are delaying the UI thread not the the process itself so what happens is you issue all the update commands but since it all runs on the same thread it gets clogged because the Thread.Sleep stops the UI thread so it runs a bunch of textBox1.Text = i.ToString(); then it stops for all the time of all the Thread.Sleep(1000); probably the number of 1->2->3... you see is equal to the number of cores in your machine.

When you stop the run method what happens is you issue one update command that runs immediately and wait for one second until you issue the next command witch I think its what you are trying to accomplish.

Thread updating GUI freezes in random moments

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