prometheus: Add CollectorRegistry.unregister functions

src/prometheus.ml

@@ -121,10 +121,16 @@ module CollectorRegistry = struct
     ensure_not_registered t info;
     t.metrics <- MetricFamilyMap.add info collector t.metrics
 
+  let unregister t info =
+    t.metrics <- MetricFamilyMap.remove info t.metrics
+
   let register_lwt t info collector =
     ensure_not_registered t info;
     t.metrics_lwt <- MetricFamilyMap.add info collector t.metrics_lwt
 
+  let unregister_lwt t info =
+    t.metrics_lwt <- MetricFamilyMap.remove info t.metrics_lwt
+
   open Lwt.Infix
 
   let map_p m =
@@ -152,6 +158,7 @@ module type METRIC = sig
   type t
   val v_labels : label_names:string list -> ?registry:CollectorRegistry.t -> help:string -> ?namespace:string -> ?subsystem:string -> string -> family
   val labels : family -> string list -> t
+  val unregister_labels : family -> string list -> unit
   val v_label : label_name:string -> ?registry:CollectorRegistry.t -> help:string -> ?namespace:string -> ?subsystem:string -> string -> (string -> t)
   val v : ?registry:CollectorRegistry.t -> help:string -> ?namespace:string -> ?subsystem:string -> string -> t
 end
@@ -197,6 +204,10 @@ end = struct
       t.children <- LabelSetMap.add label_values child t.children;
       child
 
+  let unregister_labels t label_values =
+    assert (List.length t.metric.MetricInfo.label_names = List.length label_values);
+    t.children <- LabelSetMap.remove label_values t.children
+
   let v_label ~label_name ?registry ~help ?namespace ?subsystem name =
     let family = v_labels ~label_names:[label_name] ?registry ~help ?namespace ?subsystem name in
     fun x -> labels family [x]

src/prometheus.mli

@@ -89,10 +89,16 @@ module CollectorRegistry : sig
   (** [register t metric collector] adds [metric] to the set of metrics being collected.
       It will call [collector ()] to collect the values each time [collect] is called. *)
 
+  val unregister : t -> MetricInfo.t -> unit
+  (** [unregister t metric] removes [metric] from the set of metrics being collected. *)
+
   val register_lwt : t -> MetricInfo.t -> (unit -> Sample_set.t LabelSetMap.t Lwt.t) -> unit
   (** [register_lwt t metric collector] is the same as [register t metrics collector]
       but [collector] returns [Sample_set.t LabelSetMap.t Lwt.t]. *)
 
+  val unregister_lwt : t -> MetricInfo.t -> unit
+  (** [unregister_lwt t metric] removes [metric] from the set of metrics being collected. *)
+
   val register_pre_collect : t -> (unit -> unit) -> unit
   (** [register_pre_collect t fn] arranges for [fn ()] to be called at the start
       of each collection. This is useful if one expensive call provides
@@ -124,6 +130,12 @@ module type METRIC = sig
       you may wish to write a wrapper function with labelled arguments to avoid mistakes.
       If this is called multiple times with the same set of values, the existing metric will be returned. *)
 
+  val unregister_labels : family -> string list -> unit
+  (** [unregister_labels family label_values] unregisters the metric in [family] with these values
+      for the labels. The order of the values must be the same as the order of the [label_names]
+      passed to [v_labels]; you may wish to write a wrapper function with labelled arguments to
+      avoid mistakes. *)
+
   val v_label : label_name:string -> ?registry:CollectorRegistry.t -> help:string -> ?namespace:string -> ?subsystem:string -> string -> (string -> t)
   (** [v_label] is a convenience wrapper around [v_labels] for the case where there is a single label.
       The result is a function from the single label's value to the metric. *)