44 lines
1.1 KiB
OCaml
44 lines
1.1 KiB
OCaml
(* (c) 2017 Hannes Mehnert, all rights reserved *)
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(* a ring buffer with N strings, dropping old ones *)
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type 'a t = {
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data : (Ptime.t * 'a) array ;
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mutable write : int ;
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size : int ;
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}
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let create ?(size = 1024) neutral () =
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{ data = Array.make size (Ptime.min, neutral) ; write = 0 ; size }
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let inc t = (succ t.write) mod t.size
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let write t entry =
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Array.set t.data t.write entry ;
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t.write <- inc t
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let dec t n = (pred n + t.size) mod t.size
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let not_written ts = Ptime.equal ts Ptime.min
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let entry_not_written (ts, _) = not_written ts
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let earlier than (ts, v) =
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if not_written ts then true else Ptime.is_earlier ts ~than
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let read_some tst t =
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let rec go s acc idx =
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if idx = s then (* don't read it twice *)
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acc
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else
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let entry = Array.get t.data idx in
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if tst entry then acc else go s (entry :: acc) (dec t idx)
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in
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let idx = dec t t.write in
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let entry = Array.get t.data idx in
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if tst entry then [] else go idx [entry] (dec t idx)
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let read t = read_some entry_not_written t
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let read_history t than = read_some (earlier than) t
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