store: Extract thread_local, abstract for lwt/eio

dune-project

@@ -17,6 +17,7 @@
  (depends
    (ocaml (>= "4.08"))
    ptime
+   ambient-context
    (odoc :with-doc)
    (pbrt (>= 2.3)))
  (depopts
@@ -29,6 +30,7 @@
  (synopsis "Lwt-compatible instrumentation for https://opentelemetry.io")
  (depends
    (ocaml (>= "4.08"))
+   ambient-context
    (opentelemetry (= :version))
    (cohttp-lwt-unix :with-test)
    (odoc :with-doc)

opentelemetry-lwt.opam

@@ -11,6 +11,7 @@ bug-reports: "https://github.com/imandra-ai/ocaml-opentelemetry/issues"
 depends: [
   "dune" {>= "2.7"}
   "ocaml" {>= "4.08"}
+  "ambient-context"
   "opentelemetry" {= version}
   "cohttp-lwt-unix" {with-test}
   "odoc" {with-doc}

opentelemetry.opam

@@ -12,6 +12,7 @@ depends: [
   "dune" {>= "2.7"}
   "ocaml" {>= "4.08"}
   "ptime"
+  "ambient-context"
   "odoc" {with-doc}
   "pbrt" {>= "2.3"}
 ]

src/dune

@@ -2,7 +2,7 @@
  (name opentelemetry)
  (synopsis "API for opentelemetry instrumentation")
  (flags :standard -warn-error -a+8)
- (libraries ptime ptime.clock.os pbrt threads opentelemetry.atomic)
+ (libraries ambient-context ptime ptime.clock.os pbrt threads opentelemetry.atomic)
  (public_name opentelemetry))
 
 ; ### protobuf rules ###

src/opentelemetry.ml

@@ -1,7 +1,5 @@
 (** Opentelemetry types and instrumentation *)
 
-module Thread_local = Thread_local
-
 module Lock = Lock
 (** Global lock. *)
 
@@ -522,7 +520,7 @@ module Scope = struct
 
   (**/**)
 
-  let _global_scope : t Thread_local.t = Thread_local.create ()
+  let _ambient_scope : t Ambient_context.key = Ambient_context.create_key ()
 
   (**/**)
 
@@ -530,12 +528,12 @@ module Scope = struct
   let get_surrounding ?scope () : t option =
     match scope with
     | Some _ -> scope
-    | None -> Thread_local.get _global_scope
+    | None -> Ambient_context.get _ambient_scope
 
   (** [with_scope sc f] calls [f()] in a context where [sc] is the
       (thread)-local scope, then reverts to the previous local scope, if any. *)
   let[@inline] with_scope (sc : t) (f : unit -> 'a) : 'a =
-    Thread_local.with_ _global_scope sc (fun _ -> f ())
+    Ambient_context.with_binding _ambient_scope sc (fun _ -> f ())
 end
 
 open struct

src/thread_local.ml

@@ -1,100 +0,0 @@
-module A = Opentelemetry_atomic.Atomic
-
-type key = int
-
-let[@inline] get_key_ () : key = Thread.id (Thread.self ())
-
-module Key_map_ = Map.Make (struct
-  type t = key
-
-  let compare : t -> t -> int = compare
-end)
-
-type 'a t = 'a ref Key_map_.t A.t
-(** The TLS variable is made of a global atomic reference
-    (which has very low contention: it's modified only when a
-    thread is started/stopped).
-
-    Inside that atomic variable, is a map from thread ID to a mutable [ref]
-    holding the actual data. Because this [ref] is only ever accessed
-    by the thread with this given ID, it's safe to modify. *)
-
-let create () : _ t = A.make Key_map_.empty
-
-let[@inline] get_exn (self : _ t) =
-  let m = A.get self in
-  let key = get_key_ () in
-  !(Key_map_.find key m)
-
-let[@inline] get self = try Some (get_exn self) with Not_found -> None
-
-(* remove reference for the key *)
-let remove_ref_ self key : unit =
-  while
-    let m = A.get self in
-    let m' = Key_map_.remove key m in
-    not (A.compare_and_set self m m')
-  do
-    Thread.yield ()
-  done
-
-let set_ref_ self key (r : _ ref) : unit =
-  while
-    let m = A.get self in
-    let m' = Key_map_.add key r m in
-    not (A.compare_and_set self m m')
-  do
-    Thread.yield ()
-  done
-
-(* get or associate a reference to [key], and return it.
-   Also return a function to remove the reference if we just created it. *)
-let get_or_create_ref_ (self : _ t) key ~v : _ ref * _ option =
-  try
-    let r = Key_map_.find key (A.get self) in
-    let old = !r in
-    r := v;
-    r, Some old
-  with Not_found ->
-    let r = ref v in
-    set_ref_ self key r;
-    r, None
-
-let set (self : _ t) v : unit =
-  let key = get_key_ () in
-  let _, _ = get_or_create_ref_ self key ~v in
-  ()
-
-let remove (self : _ t) : unit =
-  let key = get_key_ () in
-  remove_ref_ self key
-
-let get_or_create ~create (self : 'a t) : 'a =
-  let key = get_key_ () in
-  try
-    let r = Key_map_.find key (A.get self) in
-    !r
-  with Not_found ->
-    Gc.finalise (fun _ -> remove_ref_ self key) (Thread.self ());
-    let v = create () in
-    let r = ref v in
-    set_ref_ self key r;
-    v
-
-let with_ self v f =
-  let key = get_key_ () in
-  let r, old = get_or_create_ref_ self key ~v in
-
-  let restore_ () : unit =
-    match old with
-    | None -> remove_ref_ self key
-    | Some old -> r := old
-  in
-
-  try
-    let res = f old in
-    restore_ ();
-    res
-  with e ->
-    restore_ ();
-    raise e

src/thread_local.mli

@@ -1,27 +0,0 @@
-(** Thread/Domain local storage
-
-    This allows the creation of global state that is per-domain or per-thread.
-*)
-
-type 'a t
-
-val create : unit -> 'a t
-(** Create new storage *)
-
-val get : 'a t -> 'a option
-(** Get current value *)
-
-val get_exn : 'a t -> 'a
-(** Like {!get} but fails with an exception
-    @raise Not_found if no value was found *)
-
-val set : 'a t -> 'a -> unit
-
-val remove : _ t -> unit
-
-val get_or_create : create:(unit -> 'a) -> 'a t -> 'a
-
-val with_ : 'a t -> 'a -> ('a option -> 'b) -> 'b
-(** [with_ var x f] sets [var] to [x] for this thread, calls [f prev] where
-    [prev] is the value currently in [var] (if any), and
-    then restores the old value of [var] for this thread. *)

src/trace/dune

@@ -4,4 +4,4 @@
   (public_name opentelemetry.trace)
   (synopsis "Use opentelemetry as a collector for trace")
   (optional)
-  (libraries trace opentelemetry))
+  (libraries ambient-context trace opentelemetry))

src/trace/opentelemetry_trace.ml

@@ -1,38 +1,4 @@
 module Otel = Opentelemetry
-module TLS = Otel.Thread_local
-
-type span = Trace.span
-
-(** Table indexed by Trace spans *)
-module Span_tbl = Hashtbl.Make (struct
-  include Int64
-
-  let hash : t -> int = Hashtbl.hash
-end)
-
-(** Per-thread set of active spans. *)
-module Active_spans = struct
-  type span_begin = {
-    span_id: Otel.Span_id.t;
-    start_time: int64;
-    name: string;
-    data: (string * Trace.user_data) list;
-    __FILE__: string;
-    __LINE__: int;
-    new_scope: Otel.Scope.t;
-    old_scope: Otel.Scope.t option;
-  }
-  (** Information we get at the beginning of the span *)
-
-  type t = { tbl: span_begin Span_tbl.t } [@@unboxed]
-  (** Storage for active spans *)
-
-  let create () : t = { tbl = Span_tbl.create 8 }
-
-  let tls : t TLS.t = TLS.create ()
-
-  let[@inline] get () : t = TLS.get_or_create tls ~create
-end
 
 let conv_span_to_i64 (id : Otel.Span_id.t) : int64 =
   let bs = Otel.Span_id.to_bytes id in
@@ -47,7 +13,7 @@ let span_of_i64 (id : int64) : Otel.Span_id.t =
 
 let collector () : Trace.collector =
   let module M = struct
-    let enter_span ?__FUNCTION__:_ ~__FILE__ ~__LINE__ ~data name : span =
+    let with_span ~__FUNCTION__:_ ~__FILE__ ~__LINE__ ~data name cb =
       let span_id = Otel.Span_id.create () in
       let span = conv_span_to_i64 span_id in
 
@@ -63,45 +29,13 @@ let collector () : Trace.collector =
       let new_scope =
         { Otel.Scope.span_id; trace_id; events = []; attrs = [] }
       in
-      TLS.set Otel.Scope._global_scope new_scope;
 
-      let active_spans = Active_spans.get () in
-      Span_tbl.add active_spans.tbl span
-        {
-          span_id;
-          start_time;
-          __FILE__;
-          __LINE__;
-          old_scope;
-          new_scope;
-          name;
-          data;
-        };
+      Ambient_context.with_binding Otel.Scope._ambient_scope new_scope
+      @@ fun () ->
+      let rv = cb span in
 
-      span
-
-    let exit_span (span : span) : unit =
-      let active_spans = Active_spans.get () in
-      match Span_tbl.find_opt active_spans.tbl span with
-      | None -> () (* TODO: log warning *)
-      | Some
-          {
-            span_id;
-            start_time;
-            name;
-            __FILE__;
-            __LINE__;
-            new_scope;
-            old_scope;
-            data;
-          } ->
       let end_time = Otel.Timestamp_ns.now_unix_ns () in
 
-        (* restore previous scope *)
-        (match old_scope with
-        | None -> TLS.remove Otel.Scope._global_scope
-        | Some sc -> TLS.set Otel.Scope._global_scope sc);
-
       let o_span : Otel.Span.t =
         let attrs =
           [ "file", `String __FILE__; "line", `Int __LINE__ ] @ data
@@ -113,7 +47,14 @@ let collector () : Trace.collector =
 
       Otel.Trace.emit [ o_span ];
 
-        ()
+      rv
+
+    let enter_explicit_span ~surrounding:_ ?__FUNCTION__:_ ~__FILE__:_
+        ~__LINE__:_ ~data:_ _name : Trace.explicit_span =
+      failwith "nyi"
+
+    let exit_explicit_span _sp =
+      failwith "nyi"
 
     let message ?span ~data:_ msg : unit =
       (* gather information from context *)