Loose.MakeSourceval atomic_add :
's Carton.scheduler ->
't ->
buffers ->
('t, Uid.t, 'error, 's) store ->
hdr:(buffer:Cstruct.t -> Carton.Dec.v -> Cstruct.t) ->
Carton.Dec.v ->
((Uid.t * int, [> `Store of 'error | `Non_atomic ]) result, 's) io