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;; Atomic stack
;;;; Copyright (C) 2016 Andy Wingo <wingo@pobox.com>
;;;;
;;;; This library is free software; you can redistribute it and/or
;;;; modify it under the terms of the GNU Lesser General Public
;;;; License as published by the Free Software Foundation; either
;;;; version 3 of the License, or (at your option) any later version.
;;;;
;;;; This library is distributed in the hope that it will be useful,
;;;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
;;;; Lesser General Public License for more details.
;;;;
;;;; You should have received a copy of the GNU Lesser General Public
;;;; License along with this library; if not, write to the Free Software
;;;; Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
(define-module (fibers stack)
#:use-module (ice-9 atomic)
#:use-module (ice-9 match)
#:export (make-empty-stack
stack-empty?
stack-push!
stack-push-list!
stack-pop!
stack-pop-all!))
(define (make-empty-stack)
(make-atomic-box '()))
(define (stack-empty? stack)
(match (atomic-box-ref stack)
(() #t)
(_ #f)))
(define-inlinable (update! box f)
(let spin ((x (atomic-box-ref box)))
(call-with-values (lambda () (f x))
(lambda (x* ret)
(if (eq? x x*)
ret
(let ((x** (atomic-box-compare-and-swap! box x x*)))
(if (eq? x x**)
ret
(spin x**))))))))
(define (stack-push! sbox elt)
(update! sbox (lambda (stack) (values (cons elt stack) #f))))
(define (stack-push-list! sbox elts)
(update! sbox (lambda (stack) (values (append elts stack) #f))))
(define* (stack-pop! sbox #:optional default)
(update! sbox (lambda (stack)
(match stack
((elt . stack) (values stack elt))
(_ (values stack default))))))
(define (stack-pop-all! sbox)
(atomic-box-swap! sbox '()))
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