as suggested by @reynir @dinosaure, use a single Lwt_mutex.t

src/git_kv.ml

@@ -9,8 +9,6 @@ type t =
   ; branch : Git.Reference.t
   ; store : Store.t
   ; mutable committed : Digestif.SHA1.t option
-  ; mutable change_and_push_running : bool
-  ; condition : unit Lwt_condition.t
   ; mutex : Lwt_mutex.t
   ; mutable head : Store.hash option }
 
@@ -104,7 +102,7 @@ let connect ctx endpoint =
   init_store () >>= fun store ->
   let store = to_invalid store in
   let edn, branch = split_url endpoint in
-  let t = { ctx ; edn ; branch ; store ; committed= None; change_and_push_running= false; condition= Lwt_condition.create (); mutex= Lwt_mutex.create (); head= None } in
+  let t = { ctx ; edn ; branch ; store ; committed= None; mutex= Lwt_mutex.create (); head= None } in
   pull t >>= fun r ->
   let _r = to_invalid r in
   Lwt.return t
@@ -372,7 +370,7 @@ let of_octets ctx ~remote data =
        Result.fold ~ok:Fun.id ~error:(function `Msg msg -> failwith msg) >>= fun store ->
        analyze store data >>= fun head ->
        let edn, branch = split_url remote in
-       Lwt.return_ok { ctx ; edn ; branch ; store ; committed= None; change_and_push_running= false; condition= Lwt_condition.create (); mutex= Lwt_mutex.create (); head; })
+       Lwt.return_ok { ctx ; edn ; branch ; store ; committed= None; mutex= Lwt_mutex.create (); head; })
     (fun _exn ->
        Lwt.return_error (`Msg "Invalid PACK file"))
 
@@ -679,21 +677,8 @@ module Make (Pclock : Mirage_clock.PCLOCK) = struct
     match t.committed with
     | Some _ -> Lwt.return_error (`Msg "Nested change_and_push")
     | None ->
-      (* XXX(dinosaure): serialize [change_and_push]. If we do
+      Lwt_mutex.with_lock t.mutex (fun () ->
-         [Lwt.both (change_and_push ..) (change_and_push ..)], they can not run
+          (let open Lwt_result.Infix in
-         concurrently! The second will waiting the first to finish.
-         (reynir): Furthermore, we need to create a new task and update
-         [change_and_push_waiter] before we wait on the existing
-         [change_and_push_waiter] task without any yield point in between to
-         ensure serializability. *)
-      let open Lwt.Syntax in
-      let* () = Lwt_mutex.with_lock t.mutex @@ fun () ->
-        let rec await () =
-          if t.change_and_push_running
-          then Lwt_condition.wait ~mutex:t.mutex t.condition >>= await
-          else begin t.change_and_push_running <- true; Lwt.return_unit end in
-        await () in
-      ( let open Lwt_result.Infix in
            tree_root_hash_of_store t >>= fun tree_root_hash ->
            let t' = { t with committed = Some tree_root_hash } in
            f t' >>! fun res ->
@@ -721,13 +706,7 @@ module Make (Pclock : Mirage_clock.PCLOCK) = struct
                         >>? fun () ->
                         Store.shallow t.store hash >|= Result.ok) >>= fun () ->
              t.head <- Some hash ;
-          Lwt.return_ok res )
+             Lwt.return_ok res)
           >|= Result.map_error
-        (fun err -> `Msg (Fmt.str "error pushing %a" Store.pp_error err))
+            (fun err -> `Msg (Fmt.str "error pushing %a" Store.pp_error err)))
-      >>= fun res ->
-      let* () = Lwt_mutex.with_lock t.mutex @@ fun () ->
-        t.change_and_push_running <- false;
-        Lwt_condition.signal t.condition ();
-        Lwt.return_unit in
-      Lwt.return res
 end