feat: allow to remove backend

src/client-cohttp-lwt/opentelemetry_client_cohttp_lwt.ml

@@ -567,9 +567,8 @@ let create_backend ?(stop = Atomic.make false) ?(config = Config.make ()) () =
 
 let setup_ ?stop ?config () =
   let backend = create_backend ?stop ?config () in
-  let (module B : OT.Collector.BACKEND) = backend in
   OT.Collector.set_backend backend;
-  B.cleanup
+  OT.Collector.remove_backend
 
 let setup ?stop ?config ?(enable = true) () =
   if enable then (

src/client-ocurl/opentelemetry_client_ocurl.ml

@@ -498,7 +498,7 @@ let setup_ticker_thread ~stop ~sleep_ms (module B : Collector.BACKEND) () =
 
 let setup_ ?(stop = Atomic.make false) ?(config : Config.t = Config.make ()) ()
     =
-  let ((module B) as backend) = create_backend ~stop ~config () in
+  let backend = create_backend ~stop ~config () in
   Opentelemetry.Collector.set_backend backend;
 
   Atomic.set Self_trace.enabled config.self_trace;
@@ -508,8 +508,7 @@ let setup_ ?(stop = Atomic.make false) ?(config : Config.t = Config.make ()) ()
     let sleep_ms = min 60_000 (max 2 config.ticker_interval_ms) in
     ignore (setup_ticker_thread ~stop ~sleep_ms backend () : Thread.t)
   );
-
-  B.cleanup
+  OT.Collector.remove_backend
 
 let setup ?stop ?config ?(enable = true) () =
   if enable then (

src/core/opentelemetry.ml

@@ -3,6 +3,7 @@
 open struct
   let spf = Printf.sprintf
 
+  module Atomic = Opentelemetry_atomic.Atomic
   module Ambient_context = Opentelemetry_ambient_context
 end
 
@@ -163,33 +164,42 @@ module Collector = struct
   open struct
     let on_tick_cbs_ = AList.make ()
 
-    let backend : backend option ref = ref None
+    let backend : backend option Atomic.t = Atomic.make None
   end
 
   (** Set collector backend *)
   let set_backend (b : backend) : unit =
     let (module B) = b in
     B.set_on_tick_callbacks on_tick_cbs_;
-    backend := Some b
+    Atomic.set backend (Some b)
+
+  (** Remove current backend, if any.
+      @since NEXT_RELEASE *)
+  let remove_backend () : unit =
+    match Atomic.exchange backend None with
+    | None -> ()
+    | Some (module B) ->
+      B.tick ();
+      B.cleanup ()
 
   (** Is there a configured backend? *)
-  let[@inline] has_backend () : bool = !backend != None
+  let[@inline] has_backend () : bool = Atomic.get backend != None
 
   (** Current backend, if any *)
-  let[@inline] get_backend () : backend option = !backend
+  let[@inline] get_backend () : backend option = Atomic.get backend
 
   let send_trace (l : Trace.resource_spans list) ~ret =
-    match !backend with
+    match Atomic.get backend with
     | None -> ret ()
     | Some (module B) -> B.send_trace.send l ~ret
 
   let send_metrics (l : Metrics.resource_metrics list) ~ret =
-    match !backend with
+    match Atomic.get backend with
     | None -> ret ()
     | Some (module B) -> B.send_metrics.send l ~ret
 
   let send_logs (l : Logs.resource_logs list) ~ret =
-    match !backend with
+    match Atomic.get backend with
     | None -> ret ()
     | Some (module B) -> B.send_logs.send l ~ret
 
@@ -202,7 +212,7 @@ module Collector = struct
   (** Do background work. Call this regularly if the collector doesn't
       already have a ticker thread or internal timer. *)
   let tick () =
-    match !backend with
+    match Atomic.get backend with
     | None -> ()
     | Some (module B) -> B.tick ()