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;;; Sly
;;; Copyright © 2016 David Thompson <davet@gnu.org>
;;;
;;; Sly is free software: you can redistribute it and/or modify it
;;; under the terms of the GNU General Public License as published by
;;; the Free Software Foundation, either version 3 of the License, or
;;; (at your option) any later version.
;;;
;;; Sly 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 General Public
;;; License for more details.
;;;
;;; You should have received a copy of the GNU General Public License
;;; along with this program. If not, see
;;; <http://www.gnu.org/licenses/>.
;;; Commentary:
;;
;; Garbage collector for foreign objects.
;;
;;; Code:
(define-module (sly guardian)
#:use-module (ice-9 match)
#:use-module (sly agenda)
#:export (register-finalizer
guard
run-guardian))
(define-syntax-rule (push! variable value)
(set! variable (cons value variable)))
(define %guardian (make-guardian))
(define %finalizers '())
(define (register-finalizer predicate finalizer)
"Register FINALIZER, a procedure that frees a foreign resource, to
be used for objects that satisfy PREDICATE."
(push! %finalizers (cons predicate finalizer)))
(define (guard obj)
"Protect OBJ from garbage collection until its finalizer has been
applied. OBJ is returned unmodified."
(%guardian obj)
obj)
(define (lookup-finalizer obj)
"Return the finalization procedure for OBJ, or #f if none is found."
(let loop ((finalizers %finalizers))
(match finalizers
(() #f)
(((predicate . finalizer) . rest)
(if (predicate obj)
finalizer
(loop rest))))))
(define (run-guardian)
"Start the guardian worker coroutine on the current agenda."
(schedule-each
(lambda ()
(let loop ((obj (%guardian)))
(when obj
(let ((finalizer (lookup-finalizer obj)))
(if finalizer
(finalizer obj)
(error "no finalizer found for object" obj)))
(loop (%guardian)))))))
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