Correct & document odd Flow retry/retryWhen attempts behavior

[bubenheimer]

The Flow retry/retryWhen attempt counter never resets; it provides a kind of flow flakiness measure rather than the number of retry attempts after the last failure. This behavior is not clearly documented. I assume the behavior is an oversight, and not really by design; having such a measure seems rarely preferable. Typically, when counting retries, for example in network connectivity, the counter resets after a successful connection. Measuring flakiness would commonly be a secondary concern, perhaps as a kind of probabilistic/fuzzy measure, or for analytics.

I propose changing the behavior to the reset style, or adding a flag or new operator implementing this behavior. In addition, the behavior needs to be documented.

My present use cases for this are tied to network connectivity and interprocess communication.

[bubenheimer]

I forgot to mention that the obscurity of the present behavior is compounded by not being able to easily navigate to the source of these specific methods in the IDE (which I believe is due to current archive format limitations).

[bubenheimer]

A resetting retry count is essential also for implementing backoff (linear or exponential).

[elizarov]

This version of retry operator is far cry from the implementation of a full-blown backoff strategy. We've discussed designing providing one, but have decided that it is too domain-specific and is much better suited to be implemented in a separate library. The current version of retry operator is a mere replacement the corresponding Rx operators.

In light of the problem highlighted in this issue, we can provide a more generic version that does not have a built-in retries counter but will make it possible to keep any flow-associated state (such as retry count, last retry time, etc) to make complex retry/fail decisions. The existing retry implementations can be deprecated with a suggested replacement to more generic ones, thus, effectively, serving as an example of how you could implement a rudimentary retry counting.

[bubenheimer]

Thanks for the elaboration, makes sense!