From afbab0968340abcec044d9ac70c4a3ec0756933e Mon Sep 17 00:00:00 2001
From: Estevan Castilho <tevo@riajuu.net>
Date: Thu, 13 Aug 2026 02:35:36 +0000
Subject: Atomic swap (and monadic swap)

---
 lib/Utilities.ml  | 17 +++++++++++++++++
 lib/Utilities.mli |  6 ++++++
 2 files changed, 23 insertions(+)

diff --git a/lib/Utilities.ml b/lib/Utilities.ml
index 9ae0119..0a5bd9d 100644
--- a/lib/Utilities.ml
+++ b/lib/Utilities.ml
@@ -10,3 +10,20 @@ module Result = struct
                       ms
                       (Ok [])
 end
+
+module Atomic = struct
+  let rec swap atom f =
+    let v = Atomic.get atom in
+    let v' = f v in
+    if Atomic.compare_and_set atom v v'
+    then atom
+    else swap atom f
+
+  let rec mswap atom f =
+    let open Result in
+    let v = Atomic.get atom in
+    let* v' = f v in
+    if Atomic.compare_and_set atom v v'
+    then Ok atom
+    else mswap atom f
+end
diff --git a/lib/Utilities.mli b/lib/Utilities.mli
index cdb53df..34a03e9 100644
--- a/lib/Utilities.mli
+++ b/lib/Utilities.mli
@@ -3,3 +3,9 @@ module Result : sig
   val fmap : ('a -> ('b, 'e) result) -> ('a, 'e) result -> ('b, 'e) result
   val sequence : ('a, 'b) result list -> ('a list, 'b) result
 end
+
+module Atomic : sig
+  val swap : 'a Atomic.t -> ('a -> 'a) -> 'a Atomic.t
+  (* This is silly *)
+  val mswap : 'a Atomic.t -> ('a -> ('a, 'b) result) -> ('a Atomic.t, 'b) result
+end
-- 
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