Execute method every 15 seconds until it works

Question

I want a methode to check every 15 seconds if a specific device is connected/the driver for it used.

So something like:

Every 15 seconds 
{
if (Device is connected)
  {
   do sth.;
   exit loop;
  }      
}

So far I was able to create a Timer that seems to work:

{
System.Timers.Timer timer = new System.Timers.Timer();
timer.Interval = 15000;
timer.Elapsed += CheckConnection;
timer.Start();
}

Unfortunatly I have no real clue how to exit/abort the timer once my CheckConnection Method is true/find the device connected.

Answer 1

Here is a sample application which shows how you can use Polly's Retry policy to achieve the desired behaviour.

Let's suppose your Device class looks like this:

public class Device
{
    private int ConnectionAttempts = 0;
    private const int WhenShouldConnectionSucceed = 7;

    public bool CheckConnection() => ConnectionAttempts == WhenShouldConnectionSucceed;

    public void Connect() => ConnectionAttempts++;
}

• It increases ConnectionAttempts each time when the Connect method has been called.
• When the attempts counter equals with a predefined value then the CheckConnection will return true (this simulates the successful connection) otherwise false.

The retry policy setup looks like this:

var retry = Policy<Device>.HandleResult(result => !result.CheckConnection())
    .WaitAndRetryForever(_ => TimeSpan.FromSeconds(15),
        onRetry: (result, duration) => Console.WriteLine("Retry has been initiated"));
    
var device = new Device();
retry.Execute(() =>
{
    device.Connect();
    return device;
});

• Until a given device is not connected (!result.CheckConnection()) it will retry for ever (WaitAndRetryForever) the Connect method.
• Between each retry attempt it waits 15 seconds (TimeSpan.FromSeconds(15)).
• The onRetry delegate is used here only for demonstration purposes. onRetry is optional.

So, if I have the following simple console app:

class Program
{
    static void Main(string[] args)
    {
        var retry = Policy<Device>.HandleResult(result => !result.CheckConnection())
            .WaitAndRetryForever(_ => TimeSpan.FromSeconds(15),
                onRetry: (result, duration) => Console.WriteLine("Retry has been initiated"));

        var device = new Device();
        retry.Execute(() =>
        {
            device.Connect();
            return device;
        });
        Console.WriteLine("Device has been connected");
    }
}

then it will print the following lines to the output:

Retry has been initiated
Retry has been initiated
Retry has been initiated
Retry has been initiated
Retry has been initiated
Retry has been initiated
Device has been connected