Infinite while loop in Windows Service

Question

I have a windows in which i have added an infinite while loop in the OnStart() method .I have tested the service for 1 hour and it is running fine.But as this is my first Windows Service so have doubt on the performance with infinite loop. Here is the code..

 protected override void OnStart(string[] args)
    {
       while(true){

        string Query="";

        Query = "SELECT * FROM 'reportsetting` order by SendingTime;";

        MySqlConnection con = new MySqlConnection(conn);
        MySqlCommand comm = new MySqlCommand(Query, con);
        con.Open();
        MySqlDataReader dr = comm.ExecuteReader();
        while (dr.Read())
        {

            time = dr["SendingTime"].ToString();

            if ((str = DateTime.Now.ToString("HH:mm")).Equals(time))
            {

                //Execute Function and send reports based on the data from the database.

                Thread thread = new Thread(sendReports);
                thread.Start();

            }


        }


            //Halt for this Moment

            while ((str = DateTime.Now.ToString("HH:mm")).Equals(time))
            {


            }


         }

        }

    public void sendReports() { 



    }

So want to know if it will be Ok for long run.Thanks..

Answer 1

You almost certainly don't want to be querying a DB in an infinite loop. What you probably want to do is use a Timer to query the DB every so often (e.g. every 30 seconds) and do some work if some condition is matched e.g.

private static Timer timer;
private const int TimerInterval = 30000;

protected override void OnStart(string[] args)
{
    var callback = new TimerCallback(checkDatabase);
    this.timer = new Timer(callback, null, 0, TimerInterval);
}

private void checkDatabase()
{
    string query = "SELECT * FROM 'reportsetting` order by SendingTime;";
    using (var con = new MySqlConnection(conn))
    using (var cmd = new MySqlCommand(query, con))
    {
        con.Open();
        using (var dr = cmd.ExecuteReader())
        {
            while (dr.Read())
            {
                // do some work
            }
        }
    }
}

Depending on how important the speed of updates are, you could also be smart about things and introduce an back-off strategy. For example, here's a very simple incremental back-off:

private const int DefaultInterval = 40000;
private int interval = DefaultInterval;
...

while (dr.Read())
{
    if (someCondition)
    {
        // do some work
        timer.Change(DefaultInterval, DefaultInterval); // revert to 40 seconds 
    }
    else 
    {
        // no change? increase polling by 10 seconds
        interval += 10000;
        timer.Change(interval, interval);
    }
}

Answer 2

To re-run the query every 40 seconds:

private const string Query = "SELECT * FROM 'reportsetting` order by SendingTime;"

protected override void OnStart(string[] args)
{
    _timer = new Timer(40 * 1000); // every 40 seconds
    _timer.Elapsed += new System.Timers.ElapsedEventHandler(timer_Elapsed);
    _timer.Start(); // <- important
}

private void timer_Elapsed(object sender, System.Timers.ElapsedEventArgs e)
{
    MySqlConnection con = new MySqlConnection(conn);
    MySqlCommand comm = new MySqlCommand(Query, con);
    con.Open();
    MySqlDataReader dr = comm.ExecuteReader();
    while (dr.Read())
    {

        time = dr["SendingTime"].ToString();

        if ((str = DateTime.Now.ToString("HH:mm")).Equals(time))
        {

            //Execute Function and send reports based on the data from the database.

            Thread thread = new Thread(sendReports);
            thread.Start();
        }
    }
}

Something like that. As Groo mentioned though, you might want to dispose of the connection every time so you don't have that hanging around in memory.

Answer 3

Or you can just start it in new thread without using timer

var threadStart = new ThreadStart(<your method delegate>);
var thread = new Thread(threadStart);
thread.Start();

Answer 4

Try this

bool _IsStop = false;

protected override void OnStart(string[] args)
{
        base.OnStart(args);

        while (!this._IsStop)
        {

            this.Process();

            //40 seconds time out
            Thread.Sleep(1000*40); //1000 is 1 second
        }

        //If we reach here
        //Do some clean up here

    }


    protected override void OnStop()
    {
        //Service is stop by the user on service or by OS
        this._IsStop = true;

    }


    private void Process()
    {
        string Query = "";

        // -->>>  if you use something like this on your query and little bit setup on your db
        // this will give you a more efficient memory usage
        Query = "SELECT * FROM reportsetting where [your tag if already sent] = false and SendingTime <= [current date and time]  order by SendingTime;";

        MySqlConnection con = new MySqlConnection(conn);
        MySqlCommand comm = new MySqlCommand(Query, con);
        con.Open();
        MySqlDataReader dr = comm.ExecuteReader();
        while (dr.Read())
        {
                //Execute Function and send reports based on the data from the database.

                Thread thread = new Thread(sendReports);
                thread.Start();

                //sleep for half a second before proceeding to the next record if any
                Thread.Sleep(500); 
        }
    }