src/git_kv.ml

@@ -9,9 +9,7 @@ type t =
   ; branch : Git.Reference.t
   ; store : Store.t
   ; mutable committed : Digestif.SHA1.t option
-  ; mutable change_and_push_running : bool
+  ; mutable change_and_push_waiter : unit Lwt.t option
-  ; condition : unit Lwt_condition.t
-  ; mutex : Lwt_mutex.t
   ; mutable head : Store.hash option }
 
 let init_store () =
@@ -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; change_and_push_waiter= None; 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; change_and_push_waiter= None; head; })
     (fun _exn ->
        Lwt.return_error (`Msg "Invalid PACK file"))
 
@@ -686,13 +684,12 @@ module Make (Pclock : Mirage_clock.PCLOCK) = struct
          [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 th, wk = Lwt.wait () in
-      let* () = Lwt_mutex.with_lock t.mutex @@ fun () ->
+      let th' = t.change_and_push_waiter in
-        let rec await () =
+      t.change_and_push_waiter <- Some th;
-          if t.change_and_push_running
+      ( match th' with
-          then Lwt_condition.wait ~mutex:t.mutex t.condition >>= await
+        | None -> Lwt.return_unit
-          else begin t.change_and_push_running <- true; Lwt.return_unit end in
+        | Some th -> th ) >>= fun () ->
-        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
@@ -725,9 +722,12 @@ module Make (Pclock : Mirage_clock.PCLOCK) = struct
       >|= Result.map_error
         (fun err -> `Msg (Fmt.str "error pushing %a" Store.pp_error err))
       >>= fun res ->
-      let* () = Lwt_mutex.with_lock t.mutex @@ fun () ->
+      Lwt.wakeup_later wk () ;
-        t.change_and_push_running <- false;
+      (* (hannes) since some other task may have mutated the
-        Lwt_condition.signal t.condition ();
+         change_and_push_waiter, we only reset it to None if there's a physical
-        Lwt.return_unit in
+         equality between its value and our created task above. *)
+      (match t.change_and_push_waiter with
+       | Some th' -> if th' == th then t.change_and_push_waiter <- None
+       | None -> ());
       Lwt.return res
 end

test/fold.t

@@ -11,14 +11,12 @@ Batch operation
   > exists /bar
   > quit
   > quit
-  > EOF
   /bar exists as a value
   $ mgit git://localhost/simple#main <<EOF
   > list /
   > get /bar
   > get /foo
   > quit
-  > EOF
   - /bar
   - /foo
   00000000: 4769 7420 726f 636b 7321                 Git rocks!

test/fold2.t

@@ -9,7 +9,6 @@ Reading during batch operation
   > get /bar
   > quit
   > quit
-  > EOF
   - /bar
   00000000: 4769 7420 726f 636b 7321                 Git rocks!
   $ cd simple

test/simple.t

@@ -17,7 +17,6 @@ Simple test of our Git Key-Value store
   > get /foo
   > save db.pack
   > quit
-  > EOF
   00000000: 4865 6c6c 6f20 576f 726c 6421 0a         Hello World!.
   $ tail -c20 db.pack | hxd.xxd
   00000000: e4b2 3437 2e7e 3d7e 8508 3912 3d87 11cd  ..47.~=~..9.=...
@@ -25,7 +24,6 @@ Simple test of our Git Key-Value store
   $ mgit git://localhost/simple db.pack <<EOF
   > get /foo
   > quit
-  > EOF
   00000000: 4865 6c6c 6f20 576f 726c 6421 0a         Hello World!.
   $ cd simple
   $ echo "Git rocks!" > bar
@@ -37,7 +35,6 @@ Simple test of our Git Key-Value store
   > get /bar
   > get /foo
   > quit
-  > EOF
   + /bar
   * /
   00000000: 4769 7420 726f 636b 7321 0a              Git rocks!.