Question

I have small windows service which should write some data to web service from time of day to time of day, in regular interval which user sets up.

For ex. from 8:00 till 22:00 every 20 minutes

But after few times 10 or so triggering the callback, timer just stops, there is nothing in Event log and service is working fine meaning no exception crashed him.

Code is quite simple:

private Dictionary<string, Timer> m_timers = new Dictionary<string, Timer>();

protected override void OnStart(string[] args)
{
      // load settings

      foreach(var settings in userSettings)
      {
         SetUpTimer(settings);
      }
}

private void Callback(Settings settings)
{
    try
    {
       //Write some data to web service
       //Write to event log that web service write suceeded
    }
    catch(Exception ex)
    {
       //Write to event log
    }

    SetUpTimer(settings);
}

private void SetUpTimer(Settings settings)
{
    Timer timer;

    if (m_timers.ContainsKey(settings.Name))
    {
        timer = m_timers.Where(x => x.Key == settings.Name).Select(x => x.Value).FirstOrDefault();
        // Dispose timer (there is rumor that it can slide after few days), just to be sure.

        if (timer != null)
            timer.Dispose();
    }

    TimeSpan timeToFirstRun = settings.TimeFrom - DateTime.Now.TimeOfDay;

    while (timeToFirstRun.TotalHours < 0 || timeToFirstRun > settings.TimeTo)
    {
        timeToFirstRun += TimeSpan.FromMinutes(settings.EveryHowMuch);
    }

    if (timeToFirstRun > settings.TimeTo)
        timeToFirstRun = settings.TimeFrom - DateTime.Now.TimeOfDay + TimeSpan.FromDays(1.0);

    timer = new Timer(Callback, settings, timeToFirstRun, new TimeSpan(-1));

    if (!m_timers.ContainsKey(settings.Name))
    {
        m_timers.Add(settings.Name, timer);
    }

    // Write to event log that it sucessfully set up for next callback
}

Answer 1

Well, you have a really big flaw here:

You dispose a timer, but you don’t remove it from m_timers. The newly created timer with this name will never be added to the dictionary and will, as a consequence, get collected by the GC at some point.

Furthermore, you should be using TryGetValue instead of ContainsKey in conjunction with a LINQ query.

The top part of your method should look something like this:

Timer timer;
if(m_timers.TryGetValue(settings.Name, out timer))
{
    timer.Dispose();
    m_timers.Remove(settings.Name);
}