Add ForAttempt

[keegancsmith]

See documentation for motivation.

[keegancsmith]

In my case I want to be conservative with my memory usage. I can understand if this feature doesn't make sense for upstream given the simplicity of the current API.

[jpillora]

LGTM 👍

[DrTall]

Howdy,

I think this was a good idea and I'm looking to use it in a project, but the section where the defaults get applied (if b.Min == 0 { ...) isn't thread safe. It makes sense that the regular use case with Duration / Reset isn't threadsafe, but it is kind of a shame that ForAttempt is also not threadsafe.

I'm not sure what the best way to fix is. The projects at my company use the pattern of setting defaults via constructor, e.g.

func NewBackoffConfig() *backoffConfig {
return backoffConfig{
  Min: 100 * time.Millisecond,
  Max: 10 * time.Second,
  Factor: 2
}
}

// User code example
config := NewBackoffConfig()
config.Max = 30 * time.Second
backoff := NewBackoff(config)

And then you don't bother checking for invalid config values later on. Of course this would break existing code so it might not be doable here.

Alternatively, ForAttempt could just use the default values locally and not write them back into b. That is, basically make ForAttemptinto a value receiver method instead of pointer receiver so it isn't racy.

Any thoughts?

Thanks,
Sean