Question

I am learning creating windows services and threading. I am using a library provided by fellow worker that aids in building threaded service but this is not giving me the knowledge at the basic level.

Lets say i will have a service that will be long running (little advance than the basic example available on the net), needs to wake up every 15 seconds and then perform its action (basically will be always running). Action involves looking for a status in the DB and then performing actions.

How should the following be handled in such cases:
1. disposing the thread
2. in cases where action takes longer to execute than the interval.

I have found the following example but i am having problems with the above 2 points. Please do keep in mind that the service will be running always.

http://www.java2s.com/Tutorial/CSharp/0280__Development/CreatethedelegatethattheTimerwillcall.htm

using System;
using System.Threading;

class MainClass
{
  public static void CheckTime(Object state) 
  {
    Console.WriteLine(DateTime.Now);
  }

  public static void Main() 
  {
    TimerCallback tc = new TimerCallback(CheckTime);


    Timer t = new Timer(tc, null, 1000, 500);

    Console.WriteLine("Press Enter to exit"); 
    int i = Console.Read();

    // clean up the resources
    t.Dispose();
    t = null;
  }
}

So in my example, what will go in
1. stop event
2. Does start event looks good?
3. what should happen if nothing found in the queue?
4. What if the actions take longer than the interval?

public partial class QueueService : ServiceBase
    {


        public QueueService()
        {
            InitializeComponent();
        }

        protected override void OnStart(string[] args)
        {
            try
            {
                TimerCallback tc = new TimerCallback(CheckQueue);


            Timer t = new Timer(tc, null, 10000, 15000); //first time wait for 10seconds and then execte every 15seconds

            }
            catch (Exception ex)
            {
        what should i be checking here and then also make sure that the threading/timer doesn't stop. It should still execute every 15 seconds
            }
        }

        protected override void OnStop()
        {

        what needs to go here...

        }

        private static void CheckQueue(Object state) 
    {
            ... Connect to the DB
        ... Check status
        ... if queue status found then perform actions
        . A
        . C
        . T
        . I
        . O
        . N
        . S
        ... if end

    }

    }

Thanks for looking!

Answer 1

1. Disposing the timer.
2. Not completely. You need to declare the timer at class level otherwise it will be collected after few iterations.
3. Nothing.

4. Stop the timer before you check the queue and start it again after you finish with it. This way you won’t get into troubles of shared memory or other collisions.

   public partial class QueueService : ServiceBase
   {

   Timer timer;

    public QueueService()
    {
        InitializeComponent();
    }
   
    protected override void OnStart(string[] args)
    {
       try
       {
          TimerCallback tc = new TimerCallback(CheckQueue);
   
          timer = new Timer(tc, null, 10000, 15000);
       }
       catch (Exception ex)
       {
   
       }
   }
   
   protected override void OnStop()
   {
       if (timer != null)
           timer.Dispose();
   }
   
   private static void CheckQueue(Object state) 
   {
       timer.Change(Timeout.Infinite, 0);
   
       ... Connect to the DB
       ... Check status
       ... if queue status found then perform actions
       . A
       . C
       . T
       . I
       . O
       . N
       . S
       ... if end
   
       timer.Change(10000, 15000);
   
   }
   

   }