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open Picos
open Picos_std_event
let[@inline never] negative_count () = invalid_arg "negative count"
let[@inline never] zero_count () = invalid_arg "zero count"
type t = { count : int Atomic.t; computation : unit Computation.t }
let zero = Atomic.make 0
let create ?padded n =
if n < 0 then negative_count ();
let count =
if 0 < n then Atomic.make n |> Multicore_magic.copy_as ?padded else zero
and computation =
if n <= 0 then Computation.finished else Computation.create ()
in
Multicore_magic.copy_as ?padded { count; computation }
type _ result =
| Unit : unit result (** [Unit] is physically same as [()]. *)
| Bool : bool result (** [Bool] is physically same as [true]. *)
let rec try_decr : type a. _ -> a result -> _ -> a =
fun t result backoff ->
let n = Atomic.get t.count in
if 0 < n then
if Atomic.compare_and_set t.count n (n - 1) then begin
if n = 1 then Computation.finish t.computation;
match result with Unit -> () | Bool -> true
end
else try_decr t result (Backoff.once backoff)
else match result with Unit -> zero_count () | Bool -> false
let rec try_incr : type a. _ -> a result -> _ -> a =
fun t result backoff ->
let n = Atomic.get t.count in
if 0 < n then
if Atomic.compare_and_set t.count n (n + 1) then
match result with Unit -> () | Bool -> true
else try_incr t result (Backoff.once backoff)
else match result with Unit -> zero_count () | Bool -> false
let decr t = try_decr t Unit Backoff.default
let incr t = try_incr t Unit Backoff.default
let try_decr t = try_decr t Bool Backoff.default
let try_incr t = try_incr t Bool Backoff.default
let await t = Computation.await t.computation
let await_evt t = Event.from_computation t.computation