Visual Studio during Debugging: The function evaluation requires all threads to run

From the msdn forum:

This isn't an error in and of itself, but more of a feature of your debugger. Some properties require code to be executed in order for the property to be read, but if this requires cross-thread interaction, then other threads may have to run as well. The debugger doesn't do this automatically, but certainly can, with your permission. Just click the little evaluate icon and it will run your code and evaluate the property.

For further details on this behaviour check this excelent article

I ran into this issue when just trying to get items from a table called "AGENCY" using Entity Framework:

var agencies = db.AGENCY.OrderBy(e => e.FULLNAME);

Hovering over agencies in debug mode, clicking to expand the options, and clicking Results would give the dreaded "The function evaluation requires all threads to run" with a "Do Not Enter" icon at the end that, on which, clicking did nothing.

2 possible solutions:

1. Add .ToList() at the end:

   var agencies = db.AGENCY_TABLE.OrderBy(e => e.FULLNAME).ToList();

   List<AGENCY_TABLE> agencies = db.AGENCY_TABLE.OrderBy(e => e.FULLNAME).ToList();

   Credit goes to Hp93 for helping me come to this solution. In the comments on MUG4N's answer where I found this solution, it also mentions trying .Any() instead of .ToList(), but this gives a Boolean instead of a <T>, like <AGENCY> is, so it probably wouldn't help.

2. Workaround - try a different path in the debug options. I found that I could click on the "Non-Public Members" > "_internalQuery" > ObjectQuery > Results View and get my values that way.

MUG4N has indeed provided a correct answer however if you hover over the line of code in debug, you may be looking at something like the below. If so, click the little re-evaluate icon highlighted in the image below...

NB: I obtained this image by pinning, normally the re-evaluate icone are in the middle of the window and not down the left hand column.

You should make thread safe call because accessing Windows form controls are not Thread safe in multithreading. This is my simple code which makes Thread safe call and sets Progress bar.

public partial class Form1 : Form
{// This delegate enables asynchronous calls for setting  
    // the text property on a TextBox control.  
    delegate void StringArgReturningVoidDelegate(string text);
    private Thread demoThread = null;

    public int Progresscount = 0;
    static EventWaitHandle waithandler = new AutoResetEvent(false);
    public Form1()
    {
        InitializeComponent();
    }
    public static bool CheckForInternetConnection()
    {
        try
        {


            using (var client = new WebClient())
            {
                using (var stream = client.OpenRead("http://www.google.com"))
                {
                    return true;
                }
            }
        }
        catch
        {
            return false;
        }
    }

    public  void Progressincrement()
    {

        waithandler.WaitOne();
        while (CheckForInternetConnection()==true)
        {
            if (Progresscount==100)

            {
                break;
            }
            SetLabel("Connected");
            Progresscount += 1;

       SetProgress(Progresscount.ToString());
            Thread.Sleep(TimeSpan.FromSeconds(1));
        }
        if (Progresscount <100)
        {
            Startthread();
        }
        SetLabel("Completed");


    }

  public  void Startthread ()
        {

   this.demoThread=   new Thread(new ThreadStart(Progressincrement));
        this.demoThread.Start();
     SetLabel("Waiting for connection");
        while (CheckForInternetConnection() == false) ;

        waithandler.Set();
    }
    private void SetLabel(string text)
    {
        // InvokeRequired required compares the thread ID of the  
        // calling thread to the thread ID of the creating thread.  
        // If these threads are different, it returns true.  
        if (this.label1.InvokeRequired)
        {
            StringArgReturningVoidDelegate d = new StringArgReturningVoidDelegate(SetLabel);
            this.Invoke(d, new object[] { text });
        }
        else
        {
            this.label1.Text = text;
        }
    }
    private void SetProgress(string Value)
    {
        // InvokeRequired required compares the thread ID of the  
        // calling thread to the thread ID of the creating thread.  
        // If these threads are different, it returns true.  
        if (this.progressBar1.InvokeRequired)
        {
            StringArgReturningVoidDelegate d = new StringArgReturningVoidDelegate(SetProgress);
            this.Invoke(d, new object[] {Value});
        }
        else
        {
            this.progressBar1.Value = Convert.ToInt32(Value);
        }
    }

    private void Form1_Load(object sender, EventArgs e)
    {
        Startthread();
    }

    private void button1_Click(object sender, EventArgs e)
    {
        MessageBox.Show("Responsive");
    }
}

For more information MSDN

This isn't an error, but more of a feature of your debugger.
The debugger doesn't do this automatically, but certainly can, with users permission. Just click the little space icon and it will run the code and evaluate the property.