Which is the best way to add a retry/rollback mechanism for sync/async tasks in C#?

Question

Imagine of a WebForms application where there is a main method named CreateAll(). I can describe the process of the method tasks step by step as follows:

1) Stores to da

Answer 1

Look at using Polly for retry scenarios which seems to align well with your Pseudo code. At the end of this answer is a sample from the documentation. You can do all sorts of retry scenarios, retry and waits etc. For example, you could retry a complete transaction a number of times, or alternatively retry a set of idempotent actions a number of times and then write compensation logic if/when the retry policy finally fails.

A memento patterns is more for undo-redo logic that you would find in a word processor (Ctrl-Z and Ctrl-Y).

Other helpful patterns to look at is a simple queue, a persistent queue or even a service bus to give you eventual consistency without having to have the user wait for everything to complete successfully.

// Retry three times, calling an action on each retry 
// with the current exception and retry count
Policy
    .Handle()
    .Retry(3, (exception, retryCount) =>
    {
        // do something 
    });

A sample based on your Pseudo-Code may look as follows:

static bool CreateAll(object1 obj1, object2 obj2)
{
     // Policy to retry 3 times, waiting 5 seconds between retries.
     var policy =
         Policy
              .Handle()
              .WaitAndRetry(3, count =>
              {
                 return TimeSpan.FromSeconds(5); 
              });

       policy.Execute(() => UpdateDatabase1(obj1));
       policy.Execute(() => UpdateDatabase2(obj2));
  }