From e31f5f6aba3884e614e79a06dc4e0d4e8b1ee494 Mon Sep 17 00:00:00 2001
From: Simon Cruanes <simon.cruanes.2007@m4x.org>
Date: Wed, 19 Nov 2025 12:20:13 -0500
Subject: [PATCH] refactor: move the Mutex.protect backport into `Util_mutex`

---
 src/client-ocurl/b_queue.ml | 15 ++-------------
 src/client/batch.ml         | 19 ++++---------------
 src/core/lock.mli           |  2 ++
 src/core/opentelemetry.ml   |  4 ++++
 src/core/util_mutex.ml      | 12 ++++++++++++
 src/core/util_mutex.mli     |  1 +
 6 files changed, 25 insertions(+), 28 deletions(-)
 create mode 100644 src/core/util_mutex.ml
 create mode 100644 src/core/util_mutex.mli

diff --git a/src/client-ocurl/b_queue.ml b/src/client-ocurl/b_queue.ml
index 897ff89e..98f43876 100644
--- a/src/client-ocurl/b_queue.ml
+++ b/src/client-ocurl/b_queue.ml
@@ -1,3 +1,5 @@
+open Opentelemetry.Util_mutex
+
 type 'a t = {
   mutex: Mutex.t;
   cond: Condition.t;
@@ -7,19 +9,6 @@ type 'a t = {
 
 exception Closed
 
-(* Mutex.protect was added in OCaml 5.1, but we want support back to 4.08 *)
-(* cannot inline, otherwise flambda might move code around. (as per Stdlib) *)
-let[@inline never] protect m f =
-  Mutex.lock m;
-  match f () with
-  | x ->
-    Mutex.unlock m;
-    x
-  | exception e ->
-    (* NOTE: [unlock] does not poll for asynchronous exceptions *)
-    Mutex.unlock m;
-    Printexc.raise_with_backtrace e (Printexc.get_raw_backtrace ())
-
 let create () : _ t =
   {
     mutex = Mutex.create ();
diff --git a/src/client/batch.ml b/src/client/batch.ml
index d017355e..e508c09f 100644
--- a/src/client/batch.ml
+++ b/src/client/batch.ml
@@ -1,3 +1,5 @@
+module Otel = Opentelemetry
+
 type 'a t = {
   mutable size: int;
   mutable q: 'a list;
@@ -9,19 +11,6 @@ type 'a t = {
   mutex: Mutex.t;
 }
 
-(* Mutex.protect was added in OCaml 5.1, but we want support back to 4.08 *)
-(* cannot inline, otherwise flambda might move code around. (as per Stdlib) *)
-let[@inline never] protect_mutex m f =
-  Mutex.lock m;
-  match f () with
-  | x ->
-    Mutex.unlock m;
-    x
-  | exception e ->
-    (* NOTE: [unlock] does not poll for asynchronous exceptions *)
-    Mutex.unlock m;
-    Printexc.raise_with_backtrace e (Printexc.get_raw_backtrace ())
-
 let default_high_watermark batch_size =
   if batch_size = 1 then
     100
@@ -58,7 +47,7 @@ let ready_to_pop ~force ~now self =
 
 let pop_if_ready ?(force = false) ~now (self : _ t) : _ list option =
   let rev_batch_opt =
-    protect_mutex self.mutex @@ fun () ->
+    Otel.Util_mutex.protect self.mutex @@ fun () ->
     if ready_to_pop ~force ~now self then (
       assert (self.q <> []);
       let batch = self.q in
@@ -83,7 +72,7 @@ let rec push_unprotected (self : _ t) ~(elems : _ list) : unit =
     push_unprotected self ~elems:xs
 
 let push (self : _ t) elems : [ `Dropped | `Ok ] =
-  protect_mutex self.mutex @@ fun () ->
+  Otel.Util_mutex.protect self.mutex @@ fun () ->
   if self.size >= self.high_watermark then
     (* drop this to prevent queue from growing too fast *)
     `Dropped
diff --git a/src/core/lock.mli b/src/core/lock.mli
index 6ef1946e..2040bd1b 100644
--- a/src/core/lock.mli
+++ b/src/core/lock.mli
@@ -1,3 +1,5 @@
+(** A global lock, modifiable by the user *)
+
 val set_mutex : lock:(unit -> unit) -> unlock:(unit -> unit) -> unit
 (** Set a pair of lock/unlock functions that are used to protect access to
     global state, if needed. By default these do nothing. *)
diff --git a/src/core/opentelemetry.ml b/src/core/opentelemetry.ml
index 326c900f..ffac42b7 100644
--- a/src/core/opentelemetry.ml
+++ b/src/core/opentelemetry.ml
@@ -17,6 +17,10 @@ module AList = AList
 (** Atomic list, for internal usage
     @since 0.7 *)
 
+module Util_mutex = Util_mutex
+(** Utilities for internal usage.
+    @since NEXT_RELEASE *)
+
 (** {2 Wire format} *)
 
 module Proto = Opentelemetry_proto
diff --git a/src/core/util_mutex.ml b/src/core/util_mutex.ml
new file mode 100644
index 00000000..ab7e48a7
--- /dev/null
+++ b/src/core/util_mutex.ml
@@ -0,0 +1,12 @@
+(* Mutex.protect was added in OCaml 5.1, but we want support back to 4.08 *)
+(* cannot inline, otherwise flambda might move code around. (as per Stdlib) *)
+let[@inline never] protect m f =
+  Mutex.lock m;
+  match f () with
+  | x ->
+    Mutex.unlock m;
+    x
+  | exception e ->
+    (* NOTE: [unlock] does not poll for asynchronous exceptions *)
+    Mutex.unlock m;
+    Printexc.raise_with_backtrace e (Printexc.get_raw_backtrace ())
diff --git a/src/core/util_mutex.mli b/src/core/util_mutex.mli
new file mode 100644
index 00000000..feccf59f
--- /dev/null
+++ b/src/core/util_mutex.mli
@@ -0,0 +1 @@
+val protect : Mutex.t -> (unit -> 'a) -> 'a