78 lines
2.8 KiB
Scheme
78 lines
2.8 KiB
Scheme
;;; Guile Knots
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;;; Copyright © 2020 Christopher Baines <mail@cbaines.net>
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;;;
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;;; This file is part of Guile Knots.
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;;;
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;;; The Guile Knots is free software; you can redistribute it and/or
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;;; modify it under the terms of the GNU General Public License as
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;;; published by the Free Software Foundation; either version 3 of the
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;;; License, or (at your option) any later version.
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;;;
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;;; The Guile Knots is distributed in the hope that it will be useful,
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;;; but WITHOUT ANY WARRANTY; without even the implied warranty of
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;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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;;; General Public License for more details.
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;;;
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;;; You should have received a copy of the GNU General Public License
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;;; along with the guix-data-service. If not, see
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;;; <http://www.gnu.org/licenses/>.
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(define-module (knots promise)
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#:use-module (srfi srfi-9)
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#:use-module (ice-9 atomic)
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#:use-module (fibers)
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#:use-module (fibers conditions)
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#:export (fibers-delay
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fibers-force
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fibers-promise-reset))
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(define-record-type <fibers-promise>
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(make-fibers-promise thunk values-box evaluated-condition)
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fibers-promise?
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(thunk fibers-promise-thunk)
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(values-box fibers-promise-values-box)
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(evaluated-condition fibers-promise-evaluated-condition))
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(define (fibers-delay thunk)
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(make-fibers-promise
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thunk
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(make-atomic-box #f)
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(make-condition)))
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(define (fibers-force fp)
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(let ((res (atomic-box-compare-and-swap!
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(fibers-promise-values-box fp)
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#f
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'started)))
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(if (eq? #f res)
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(call-with-values
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(lambda ()
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(with-exception-handler
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(lambda (exn)
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(atomic-box-set! (fibers-promise-values-box fp)
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exn)
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(signal-condition!
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(fibers-promise-evaluated-condition fp))
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(raise-exception exn))
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(fibers-promise-thunk fp)
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#:unwind? #t))
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(lambda vals
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(atomic-box-set! (fibers-promise-values-box fp)
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vals)
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(signal-condition!
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(fibers-promise-evaluated-condition fp))
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(apply values vals)))
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(if (eq? res 'started)
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(begin
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(wait (fibers-promise-evaluated-condition fp))
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(let ((result (atomic-box-ref (fibers-promise-values-box fp))))
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(if (exception? result)
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(raise-exception result)
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(apply values result))))
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(if (exception? res)
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(raise-exception res)
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(apply values res))))))
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(define (fibers-promise-reset fp)
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(atomic-box-set! (fibers-promise-values-box fp)
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#f))
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