Question

I constantly have some situations in which I have to retry some operations if they fail, giving up after certain number of times, and taking a short breaks between attempts.

Is there a way to create a ‘retry method’ that will enable me not to copy the code around every time I do that?

Answer 1

Got tired of copy/paste the same code over and over again, so I created a method that accepts the delegate of the task that has to be done. Here it is:

//  logger declaration (I use NLog)
private static readonly Logger Log = LogManager.GetCurrentClassLogger();
delegate void WhatTodo();
static void TrySeveralTimes(WhatTodo Task, int Retries, int RetryDelay)
{
    int retries = 0;
    while (true)
    {
        try
        {
            Task();
            break;
        }
        catch (Exception ex)
        {
            retries++;
            Log.Info<string, int>("Problem doing it {0}, try {1}", ex.Message, retries);
            if (retries > Retries)
            {
                Log.Info("Giving up...");
                throw;
            }
            Thread.Sleep(RetryDelay);
        }
    }
}

To use it, I would simply write:

TrySeveralTimes(() =>
{
    string destinationVpr = Path.Combine(outdir, "durations.vpr");
    File.AppendAllText(destinationVpr, file + ",     " + lengthInMiliseconds.ToString() + "\r\n");
}, 10, 100);

In this example I am appending a file that gets locked with some external process, only way to write it is to retry it several times until the process is done with it…

I would sure love to see better ways of handling this particular pattern (retrying).

EDIT: I looked at Gallio in another answer, and it is really great. Look at this example:

Retry.Repeat(10) // Retries maximum 10 times the evaluation of the condition.
         .WithPolling(TimeSpan.FromSeconds(1)) // Waits approximatively for 1 second between each evaluation of the condition.
         .WithTimeout(TimeSpan.FromSeconds(30)) // Sets a timeout of 30 seconds.
         .DoBetween(() => { /* DoSomethingBetweenEachCall */ })
         .Until(() => { return EvaluateSomeCondition(); });

It does everything. It will even watch your kids while you code 🙂 But, I strive for simplicity, and still am using .NET 2.0. So I guess that my example will still be of some use to you.