Aside from using a timer in c#

Question

I'm trying to write a program that keeps executing a method without having to use a timer. For example, I want to have a program that shows a list of currently running processes. Obviously, it's constantly changing. I don't want to use a timer that gets the list of processes every second and adds them to the list, because it doesn't look very elegant to me. Is there any special way to do that? How can I make a service that would make this happen?

Answer 1

Personally, I would stick with a timer for this. It really is pretty elegant. But, if you really want something with a bit more pizazz then read on!

As the new async and await keywords (to be included in C# 5.0) catch on we may see timers getting more uncool¹. Here is how you could do this without a timer right now using the Async CTP.

private async void ShowProcessesButton_Click(object sender, EventArgs args)
{
  while (true)
  {
    await Task.Delay(1000);  // TaskEx.Delay in the CTP
    YourListBox.Items.Clear();
    foreach (Process p in Process.GetProcesses())
    {
      YourListBox.Items.Add(p.ProcessName);
    }
  }
}

Pretty weird huh? It is probably not the ideal example of how async and await are suppose to be used, but you get the point. It is the wave of the future to come.

---

¹Do not get me wrong. There will always be a need for the traditional timer classes.

Answer 2

You can spawn a lower priority thread with an infinite (until the process exits) loop to update your process list periodically. Without more information about what kind of control you're using or whatever I can't really help you out with Control update delegates, but the rough skeleton of your function would be:

    private void processUpdater()
    {
        while (true) //not the most elegant way to implement a pseudo-infinite loop, but you can figure out how you want to signal it to end.
        {
            var runningProcesses = Process.GetProcesses().Where(p => !string.IsNullOrEmpty(p.MainWindowTitle)).Select(p => p.MainWindowTitle); //filter the running processes to get those with open windows.
            this.lstProcesses.Invoke((MethodInvoker)delegate { this.lstProcesses.Items.Clear(); }); //thread-safe invocation to clear the current items
            this.lstProcesses.Invoke((MethodInvoker)delegate { this.lstProcesses.Items.AddRange(runningProcesses.ToArray<string>()); }); //add the new set of windowed processes
            System.Threading.Thread.Sleep(5000); //update the list every 5 seconds
        }
    }

In my case I just capture the processes with windows, and list those windows titles in a listbox (lstProcesses)

Now, to spawn this thread:

var tUpdater = new System.Threading.Thread(processUpdater);
tUpdater.Priority = System.Threading.ThreadPriority.BelowNormal;
tUpdater.Name = "Process List Updater";
tUpdater.Start(); //start the thread running.

Obviously this is a very basic implementation, but hopefully it'll give you a rough idea on how to do what you want.

Answer 3

If you're dead set on not using a Timer, you will need to do something like:

1. Get the list or running processes when your app starts up
2. Detect when a process starts and add it to the list
3. Detect when a process ends and remove it from the list

To detect process creation/termination, take a look at this answer:

https://stackoverflow.com/a/3556280/64290

Answer 4

Program1:

You can develop a Windows service which runs constantly. No timer is required. If you can give us some more details, we can come up with a better solution. But remember, no user interaction is possible for a window service.

The running processes are added to an observablecollection. When ever an item is added it raises CollectionChanged event.

Program2:

You can have a program where you want the list of running processes exposed as a Webservice, the webservice is consumed in Program1. In the CollectionChanged eventhandler of program1, you can invoke program2 webservice and notify about the newly added process.

Answer 5

I don't agree with the comments suggesting that Timers are the only or best answer here. The desire to be alerted when a change occurs, rather than polling for it, is a noble pursuit. You're looking for a WinAPI "Hook", I believe, but I don't know which one or if it exists.

See http://msdn.microsoft.com/en-us/library/windows/desktop/ms644959%28v=vs.85%29.aspx

Also: Win API: Hook every window show or process execution