CPU friendly infinite loop

Question

Writing an infinite loop is simple:

while(true){
    //add whatever break condition here
}

But this will trash the CPU performance. This execution thread will take as much as possible from CPU's power.

What is the best way to lower the impact on CPU? Adding some Thread.Sleep(n) should do the trick, but setting a high timeout value for Sleep() method may indicate an unresponsive application to the operating system.

Let's say I need to perform a task each minute or so in a console app. I need to keep Main() running in an "infinite loop" while a timer will fire the event that will do the job. I would like to keep Main() with the lowest impact on CPU.

What methods do you suggest. Sleep() can be ok, but as I already mentioned, this might indicate an unresponsive thread to the operating system.

LATER EDIT:

I want to explain better what I am looking for:

1. I need a console app not Windows service. Console apps can simulate the Windows services on Windows Mobile 6.x systems with Compact Framework.

2. I need a way to keep the app alive as long as the Windows Mobile device is running.

3. We all know that the console app runs as long as its static Main() function runs, so I need a way to prevent Main() function exit.

4. In special situations (like: updating the app), I need to request the app to stop, so I need to infinitely loop and test for some exit condition. For example, this is why Console.ReadLine() is no use for me. There is no exit condition check.

5. Regarding the above, I still want Main() function as resource friendly as possible. Let asside the fingerprint of the function that checks for the exit condition.

Answer 1

To expound on a comment CodeInChaos made:

You can set a given thread's priority. Threads are scheduled for execution based on their priority. The scheduling algorithm used to determine the order of thread execution varies with each operating system. All threads default to "normal" priority, but if you set your loop to low; it shouldn't steal time from threads set to normal.

Answer 2

The Timer approach is probably your best bet, but since you mention Thread.Sleep there is an interesting Thread.SpinWait or SpinWait struct alternative for similar problems that can sometimes be better than short Thread.Sleep invocations.

Also see this question: What's the purpose of Thread.SpinWait method?

Answer 3

You can use System.Threading.Timer Class which provides ability to execute callback asynchronously in a given period of time.

public Timer(
    TimerCallback callback,
    Object state,
    int dueTime,
    int period
)

As alternative there is System.Timers.Timer class which exposes Elapsed Event which raises when a given period of time is elapsed.

Answer 4

I did this for an application that had to process files as they were dropped on a folder. Your best bet is a timer (as suggested) with a Console.ReadLine() at the end of "main" without putting in a loop.

Now, your concern about telling the app to stop:

I have also done this via some rudimentary "file" monitor. Simply creating the file "quit.txt" in the root folder of the application (by either my program or another application that might request it to stop) will make the application quit. Semi-code:

<do your timer thing here>
watcher = new FileSystemWatcher();
watcher.Path = <path of your application or other known accessible path>;
watcher.Changed += new FileSystemEventHandler(OnNewFile);
Console.ReadLine();

The OnNewFile could be something like this:

private static void OnNewFile(object source, FileSystemEventArgs e)
{
    if(System.IO.Path.GetFileName(e.FullPath)).ToLower()=="quit.txt")
        ... remove current quit.txt
        Environment.Exit(1);
}

Now you mentioned that this is (or could be) for a mobile application? You might not have the file system watcher. In that case, maybe you just need to "kill" the process (you said "In special situations (like: updating the app), I need to request the app to stop". Whoever the "requester" to stop it is, should simply kill the process)

Answer 5

Lots of "advanced" answers here but IMO simply using a Thread.Sleep(lowvalue) should suffice for most.

Timers are also a solution, but the code behind a timer is also an infinity loop - I would assume - that fires your code on elapsed intervals, but they have the correct infinity-loop setup.

If you need a large sleep, you can cut it into smaller sleeps.

So something like this is a simple and easy 0% CPU solution for a non-UI app.

static void Main(string[] args)
{
    bool wait = true;
    int sleepLen = 1 * 60 * 1000; // 1 minute
    while (wait)
    {

        //... your code

        var sleepCount = sleepLen / 100;
        for (int i = 0; i < sleepCount; i++)
        {
            Thread.Sleep(100);
        }
    }
}

Regarding how the OS detects if the app is unresponsive. I do not know of any other tests than on UI applications, where there are methods to check if the UI thread processes UI code. Thread sleeps on the UI will easily be discovered. The Windows "Application is unresponsive" uses a simple native method "SendMessageTimeout" to see detect if the app has an unresponse UI.

Any infinity loop on an UI app should always be run in a separate thread.

Answer 6

Why would you condone the use of an infinite loop? For this example would setting the program up as a scheduled task, to be run every minute, not be more economical?