robur/git-kv
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as suggested by @reynir @dinosaure, use a single Lwt_mutex.t

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Hannes Mehnert 2024-10-29 11:51:55 +01:00
parent 681e4f2367
commit 0b330178e1
1 changed files with 34 additions and 55 deletions
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89
src/git_kv.ml
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@ -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"))
@ -679,55 +677,36 @@ 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.both (change_and_push ..) (change_and_push ..)], they can not run
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 ->
(* XXX(dinosaure): we assume that only [change_and_push] can reset [t.committed] to [None] and
we ensured that [change_and_push] can not be called into [f]. So we are sure that [t'.committed]
must be [Some _] in anyway. *)
let[@warning "-8"] Some new_tree_root_hash = t'.committed in
if Digestif.SHA1.equal new_tree_root_hash tree_root_hash
then Lwt.return_ok res (* XXX(dinosaure): nothing to send! *)
else if not (Option.equal Digestif.SHA1.equal t.head t'.head) then
Lwt.return (Error (`Msg "store was modified outside of change_and_push, please retry"))
else
let action = Option.fold ~none:(`Create t.branch) ~some:(fun _ -> `Update (t.branch, t.branch)) t.head in
let parents = Option.to_list t.head in
let author = author ?name ?email now in
let committer = author in
let commit = Store.Value.Commit.make ~tree:new_tree_root_hash ~author ~committer
~parents (Some message) in
Store.write t.store (Git.Value.Commit commit) >>= fun (hash, _) ->
Store.Ref.write t.store t.branch (Git.Reference.uid hash) >>= fun () ->
Lwt.Infix.(Sync.push ~capabilities ~ctx:t.ctx t.edn t.store [ action ]
>|= Result.map_error (fun err ->
`Msg (Fmt.str "error pushing branch %a: %a"
Git.Reference.pp t.branch Sync.pp_error err))
>>? fun () ->
Store.shallow t.store hash >|= Result.ok) >>= fun () ->
t.head <- Some hash ;
Lwt.return_ok res )
>|= 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 () ->
t.change_and_push_running <- false;
Lwt_condition.signal t.condition ();
Lwt.return_unit in
Lwt.return res
Lwt_mutex.with_lock t.mutex (fun () ->
(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 ->
(* XXX(dinosaure): we assume that only [change_and_push] can reset [t.committed] to [None] and
we ensured that [change_and_push] can not be called into [f]. So we are sure that [t'.committed]
must be [Some _] in anyway. *)
let[@warning "-8"] Some new_tree_root_hash = t'.committed in
if Digestif.SHA1.equal new_tree_root_hash tree_root_hash
then Lwt.return_ok res (* XXX(dinosaure): nothing to send! *)
else if not (Option.equal Digestif.SHA1.equal t.head t'.head) then
Lwt.return (Error (`Msg "store was modified outside of change_and_push, please retry"))
else
let action = Option.fold ~none:(`Create t.branch) ~some:(fun _ -> `Update (t.branch, t.branch)) t.head in
let parents = Option.to_list t.head in
let author = author ?name ?email now in
let committer = author in
let commit = Store.Value.Commit.make ~tree:new_tree_root_hash ~author ~committer
~parents (Some message) in
Store.write t.store (Git.Value.Commit commit) >>= fun (hash, _) ->
Store.Ref.write t.store t.branch (Git.Reference.uid hash) >>= fun () ->
Lwt.Infix.(Sync.push ~capabilities ~ctx:t.ctx t.edn t.store [ action ]
>|= Result.map_error (fun err ->
`Msg (Fmt.str "error pushing branch %a: %a"
Git.Reference.pp t.branch Sync.pp_error err))
>>? fun () ->
Store.shallow t.store hash >|= Result.ok) >>= fun () ->
t.head <- Some hash ;
Lwt.return_ok res)
>|= Result.map_error
(fun err -> `Msg (Fmt.str "error pushing %a" Store.pp_error err)))
end