Issue #11/clearing default registry

[codification]

I added a simple test-case illustrating the issue as well as a workaround. Also added a caveat to the README.
Use if you like.

[codification]

Regarding #11

[marco-m]

@xsc any news about this PR ? Should it be accepted, modified or declined ?

[delitescere]

The problem is that things can register collectors with the default registry outside of the Iapetos lifecycle (e.g. log4j2).

The latest changes to Iapetos allow easy registering/de-registering (and clearing) of collectors Iapetos has handled. In no circumstances should Iapetos de-register or clear anything it hasn't registered.

If you're using something like Sierra's components life is now very good:

(ns component.prometheus
  (:require [com.stuartsierra.component :refer [Lifecycle start stop]]
            [iapetos.core :as metrics]))

(defrecord Prometheus []
  Lifecycle

  (start [component]
    (-> component
      (assoc :registry ((apply comp (:metrics-collectors component)) metrics/default-registry))))

  (stop [component]
    (try
      (metrics/clear (:registry component))
      (catch Exception _))
    (-> component
      (assoc :metrics-collectors nil)
      (assoc :registry nil))))

Note the metrics/default-registry in the start, and the metrics/clear in the stop. 💯

[marco-m]

thanks for the explanation!

[MalloZup]

@delitescere @marco-m @codification . I didn't dive to much on this PR but afaik what stated here: #12 (comment)
make this PR not desirable to merge.

Please correct me if I am wrong thx.

[MalloZup]

I'm losing this since is resolved thx!