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ExponentialRetryPolicy materializes GetIntervals()

See original GitHub issue

The constructor of ExponentialRetryPolicy materializes the IEnumerable<TimeSpan> returned from GetIntervals(). This seems directly opposed to its nature:

It is an iterator function.
It treats Int32.MaxValue as unlimited.

When using retryLimit: Int32.MaxValue, which GetIntervals() explicitly special-cases, the loop is infinite (until ToArray() tries to allocate an array that is too large).

Even when avoiding Int32.MaxValue, when trying to accommodate a very large number of attempts, the materialized array can take a lot of memory, when the intervals could just be calculated on-the-fly. Materialization also incurs a lot of calls to Random.Next() that would otherwise have been amortized over the lifetime of the policy instance.

A good alternative property type to TimeSpan[] might be IEnumerator<TimeSpan>, since it enforces forward-only behavior. It is a public property, unfortunately, so I’m not sure how far the impact reaches.

I ran into this issue when I was trying to use exponential message retries in MassTransit 7.0.7.