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(*
* Copyright (c) 2015, Théo Laurent <theo.laurent@ens.fr>
* Copyright (c) 2015, KC Sivaramakrishnan <sk826@cl.cam.ac.uk>
*
* Permission to use, copy, modify, and/or distribute this software for any
* purpose with or without fee is hereby granted, provided that the above
* copyright notice and this permission notice appear in all copies.
*
* THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
* WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
* MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
* ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
* WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
* ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
* OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
*)
(* Michael-Scott queue copied over from [saturn](github.com/ocaml-multicore/saturn) *)
module Atomic = Dscheck.TracedAtomic
type 'a node = Nil | Next of 'a * 'a node Atomic.t
type 'a t = { head : 'a node Atomic.t; tail : 'a node Atomic.t }
let create () =
let head = Next (Obj.magic (), Atomic.make Nil) in
{ head = Atomic.make_contended head; tail = Atomic.make_contended head }
let is_empty q =
match Atomic.get q.head with
| Nil -> failwith "MSQueue.is_empty: impossible"
| Next (_, x) -> ( match Atomic.get x with Nil -> true | _ -> false)
let pop q =
let rec loop () =
let s = Atomic.get q.head in
let nhead =
match s with
| Nil -> failwith "MSQueue.pop: impossible"
| Next (_, x) -> Atomic.get x
in
match nhead with
| Nil -> None
| Next (v, _) when Atomic.compare_and_set q.head s nhead -> Some v
| _ -> loop ()
in
loop ()
let push q v =
let rec find_tail_and_enq curr_end node =
if Atomic.compare_and_set curr_end Nil node then ()
else
match Atomic.get curr_end with
| Nil -> find_tail_and_enq curr_end node
| Next (_, n) -> find_tail_and_enq n node
in
let newnode = Next (v, Atomic.make Nil) in
let tail = Atomic.get q.tail in
match tail with
| Nil -> failwith "HW_MSQueue.push: impossible"
| Next (_, n) ->
find_tail_and_enq n newnode;
ignore (Atomic.compare_and_set q.tail tail newnode)
|
