Question

I am trying to change the priority of a thread but I can’t get it to work. I have made a button which toggles the priority between low and high and when I am checking this in the joblist the priority is changed. But the CPU usage isn’t changed. I wonder if this is just because I don’t use the full CPU power or how this can be.

I am not asking if it is a good idea. I am asking how to do it.

Here is how I change the priority. This is the code behind class:

    private Thread tr;

    public MainWindow()
    {
        InitializeComponent();

        tr = new Thread(new ThreadStart(infiniteLoop));
        tr.Start();
    }

    private void Button_Click(object sender, RoutedEventArgs e)
    {
        if (Process.GetCurrentProcess().PriorityClass == ProcessPriorityClass.High)
        {
            Process.GetCurrentProcess().PriorityClass = ProcessPriorityClass.Idle;
            tr.Priority = ThreadPriority.Lowest;
            description.Text = "Idle";
        }

        else
        {
            Process.GetCurrentProcess().PriorityClass = ProcessPriorityClass.High;
            tr.Priority = ThreadPriority.Highest;
            description.Text = "High";
        }
    }

    private void infiniteLoop()
    {
        while (true)
        {
        }
    }

Answer 1

It doesn’t work how I think you expect it to – i.e. that a process with low priority is somehow throttled to x% CPU time.

A single-threaded process with any priority can consume 100% of CPU time on one core.

When you have two processes, one with higher priority than the other, that would both consume 100% CPU time on their own, executing simultaneously, the one with higher priority will get all of the CPU time (assuming a single core) and the one with lower priority will not progress at all.

The priority of a process is simply used to determine the order in which the scheduler will “hand out” CPU time slices to processes.