c# - Why does GetWindowText hang with a "closed" handle but not with a random one

Question

Using the following code

    [DllImport("user32.dll", EntryPoint = "GetWindowText", ExactSpelling = false, CharSet = CharSet.Auto, SetLastError = true)]
    private static extern int GetWindowText(IntPtr hWnd, StringBuilder lpWindowText, int nMaxCount);

    public static String GetWindowText(IntPtr hWnd)
    {
        StringBuilder title = new StringBuilder(MAX_TITLE_LENGTH);            
        int titleLength = WinAPI.GetWindowText(hWnd, title, title.Capacity + 1);
        title.Length = titleLength;
        return title.ToString();
    }

GetWindowText will hang (IE: never return) if passed a handle to a recently closed application. (Which is odd to me because I would have thought it would just return with a zero value)

Passing in random handle such as new IntPtr(123456) succeeds and returns with no value.

Could anyone please explain this behavior?

Answer 1

Read here a description of GetWindowText undercovers: The secret life of GetWindowText.

I don't think you'll ever get a better one :-) If you really want to be 100% sure you won't hang calling it, you need to do it on another thread that you can manage yourself (ie: kill if you need to)