#| -*-Scheme-*-

Copyright (C) 1986, 1987, 1988, 1989, 1990, 1991, 1992, 1993, 1994,
    1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005,
    2006, 2007, 2008, 2009, 2010, 2011, 2012, 2013, 2014, 2015, 2016,
    2017, 2018, 2019 Massachusetts Institute of Technology

This file is part of MIT/GNU Scheme.

MIT/GNU Scheme 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 2 of the License, or (at
your option) any later version.

MIT/GNU Scheme 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 MIT/GNU Scheme; if not, write to the Free Software
Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301,
USA.

|#

;;;; Protection lists
;;; package: (win32)

(declare (usual-integrations))

;; A protection list has a header cons cell.
;; Elements of the list are weak pairs (thing . info)
;; The car of the header contains the finalization procedure which is called
;; on the info field when the THING disappears.

(define-structure
  (protection-list
    (conc-name protection-list/)
    (constructor %make-protection-list))              
  head)


(define (make-protection-list finalizer)
  (let* ((header  (cons finalizer '()))
         (p       (%make-protection-list header)))
    (protection-list/add! *protection-lists* p header)
    p))


(define (protection-list/add! p thing info)
  ;; we return the weak pair allocated so that we can use it to get at thing
  ;; if this is really needed
  ;; do we need to wrap this in a without-interrupts?
  (let* ((weakpr  (weak-cons thing info))
         (link    (cons weakpr #f))
         (header  (protection-list/head p)))
    (let ((tail (cdr header)))
      (set-cdr! link tail)
      (set-cdr! header link)
      weakpr)))

(define (protection-list/finalize! p)
  ;; During finalization, the list is set to '().  This allows items
  ;; to be added to the list during finalization.  The call to append!
  ;; merges the new and old lists
  (let*  ((header    (if (protection-list? p)
                         (protection-list/head p)
			 p))
          (items     (cdr header))
          (finalize! (car header)))

    (define (loop/no-head items)
      (if (pair? items)
          (if (weak-car (car items))
	      (loop/with-head items items (cdr items))
	      (begin (finalize! (weak-cdr (car items)))
	             (loop/no-head (cdr items))))
	  '()))

    (define (loop/with-head first-cons mutate-point items)
      (if (pair? items)
	  (if (weak-car (car items))
	      (begin
		(set-cdr! mutate-point items)
		(loop/with-head first-cons items (cdr items)))
	      (begin
		(finalize! (weak-cdr (car items)))
		(set-cdr! mutate-point (cdr items))
		(loop/with-head first-cons mutate-point (cdr items))))
	  first-cons))

    (set-cdr! header '())
    (set-cdr! header (append! (cdr header) (loop/no-head items)))))


(define (protection-list/empty? p)
  (null? (cdr (protection-list/head p))))


(define (protection-list/finalize-protection-list hd)
  ;; if the list is still protecting something then add it back to the
  ;; master list
  (if (pair? (cdr hd))
    (protection-list/add! *protection-lists* (%make-protection-list hd) hd)))

(define (protection-list/gc-daemon)
;(display ";; protection-list/gc-daemon\n")
  (for-each (lambda (wp)
;              (display ";;Finalizing ") (display (weak-car wp)) (newline)
              (protection-list/finalize! (weak-cdr wp)))
            (cdr (protection-list/head *protection-lists*)))
  (protection-list/finalize! *protection-lists*))	      

(define (protection-list/for-each action p)
  (define (loop items)
    (if (pair? items)
      (begin
	(if (weak-car (car items))
	  (action (weak-car (car items))))
	(loop (cdr items)))))
  (loop (cdr (protection-list/head p))))

(define (protection-list/for-each-info action p)
  (define (loop items)
    (if (pair? items)
      (begin
	(if (weak-car (car items))
	  (action (weak-cdr (car items))))
	(loop (cdr items)))))
  (loop (cdr (protection-list/head p))))

(define (protection-list/find pred p)
  (define (loop items)
    (if (pair? items)
      (let* ((item  (car items))
	     (thing (weak-car item)))
	(if (and (weak-pair/car? item) (pred thing))
	    thing
	    (loop (cdr items))))
      #f))
  (loop (cdr (protection-list/head p))))
	  

(define *protection-lists*)

;(define p+ protection-list/add!)
(define (gc) (gc-flip) (protection-list/gc-daemon))

(define (initialize-protection-list-package!)
  (set! *protection-lists*
    (%make-protection-list
      (cons protection-list/finalize-protection-list '())))
  (add-gc-daemon! protection-list/gc-daemon)
)

                          