albatross/src/vmm_ring.ml

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2017-05-26 14:30:34 +00:00
(* (c) 2017 Hannes Mehnert, all rights reserved *)
(* a ring buffer with N strings, dropping old ones *)
type t = {
data : (Ptime.t * string) array ;
mutable write : int ;
size : int ;
}
let create ?(size = 1024) () =
{ data = Array.make 1024 (Ptime.min, "") ; write = 0 ; size }
let inc t = (succ t.write) mod t.size
let write t v =
Array.set t.data t.write v ;
t.write <- inc t
let dec t n = (pred n + t.size) mod t.size
let earlier ts than =
if ts = Ptime.min then true
else Ptime.is_earlier ts ~than
let read_history t than =
let rec go s acc idx =
if idx = s then (* don't read it twice *)
acc
else
let ts, v = Array.get t.data idx in
if earlier ts than then acc
else go s ((ts, v) :: acc) (dec t idx)
in
let idx = dec t t.write in
let ts, v = Array.get t.data idx in
if earlier ts than then []
else go idx [(ts,v)] (dec t idx)