C# .NET 2 Threading.Timer - time drifting

Question

I have a dll consumed by a service. Its basic job is to run every X minutes and perform some system checks. In my dll I have a top level class that declares a System.threading.timer and a Timercallback. The constructor for the class initialises the timerCallback with my thread function. In my "Onstart" handler I initialise the timer with the timercallback and set the next time to fire and interval time. In my case its every 10 minutes. Usually in these 10 minute checks there is nothing to do but the service is forced to do something at least once every day at a set time.

My problem: I am finding that during testing, the time the daily check is carried out every day is slowly drifitng away from the desired start time of 8.30. e.g. over about 20 odd days my time has drifted from 08.30 to 08.31.35. It drifts about 4 - 6 seconds every day.

My question: does anyone know why the time is drifting like this and how can I make it stick to its allotted time?

thanks

Answer 1

The time "drifts" because the timer is simply not that precise. If you need to run your code as closely as possible to a certain interval, you can do something like this:

public void MyTimerCallback(object something) {
    var now = DateTime.UtcNow;
    var shouldProbablyHaveRun = new DateTime(
        now.Year, now.Month, now.Day,
        now.Hour, now.Minute - (now.Minute % 10), 0);
    var nextRun = shouldProbablyHaveRun.AddMinutes(10.0);

    // Do stuff here!

    var diff = nextRun - DateTime.UtcNow;
    timer.Change(diff, new TimeSpan(-1));
}

...assuming you are using a System.Threading.Timer instance. Modify the example if you are using any other type of timer (there are several!).