#| -*-Scheme-*-

$Id: gc.scm,v 14.25 2007/01/05 21:19:28 cph Exp $

Copyright (C) 1986, 1987, 1988, 1989, 1990, 1991, 1992, 1993, 1994,
    1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005,
    2006, 2007 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.

|#

;;;; Garbage Collector
;;; package: (runtime garbage-collector)

(declare (usual-integrations))

(define (initialize-package!)
  (set! gc-boot-loading? #t)
  (set! hook/gc-flip default/gc-flip)
  (set! hook/purify default/purify)
  (set! hook/stack-overflow default/stack-overflow)
  (set! hook/hardware-trap default/hardware-trap)
  (set! default-safety-margin 4500)
  (set! pure-space-queue (list 'PURE-SPACE-QUEUE))
  (set! constant-space-queue (list 'CONSTANT-SPACE-QUEUE))
  (set! hook/gc-start default/gc-start)
  (set! hook/gc-finish default/gc-finish)
  (let ((fixed-objects (get-fixed-objects-vector)))
    (let ((interrupt-vector (vector-ref fixed-objects 1)))
      (vector-set! interrupt-vector 0 condition-handler/stack-overflow)
      (vector-set! interrupt-vector 2 condition-handler/gc))
    (vector-set! fixed-objects #x0C condition-handler/hardware-trap)
    ((ucode-primitive set-fixed-objects-vector!) fixed-objects)))

(define (condition-handler/gc interrupt-code interrupt-enables)
  interrupt-code interrupt-enables
  (hook/gc-flip default-safety-margin))

(define (condition-handler/stack-overflow interrupt-code interrupt-enables)
  interrupt-code
  (hook/stack-overflow)
  (set-interrupt-enables! interrupt-enables))

(define (condition-handler/hardware-trap escape-code)
  ((ucode-primitive set-trap-state!)
   ((ucode-primitive set-trap-state!) 2)) ; Ask.
  (hook/hardware-trap escape-code))

(define hook/gc-flip)
(define hook/purify)
(define hook/stack-overflow)
(define hook/hardware-trap)
(define default-safety-margin)

(define (default/gc-flip safety-margin)
  (let ((try-queue
	 (lambda (queue pure?)
	   (let ((items (cdr queue)))
	     (and (pair? items)
		  (let ((result
			 (purify-internal (if (pair? (cdr items))
					      items
					      (car items))
					  pure?
					  safety-margin)))
		    (and (pair? result)
			 (begin
			   (if (car result)
			       (set-cdr! queue '())
			       (begin
				 (set-cdr! queue (cdr items))
				 (queued-purification-failure)))
			   (cdr result)))))))))
    (or (try-queue pure-space-queue #t)
	(try-queue constant-space-queue #f)
	(gc-flip-internal safety-margin))))

(define (queued-purification-failure)
  (warn "Unable to purify all queued items; dequeuing one."))

(define (default/purify item pure-space? queue?)
  (if (not (if pure-space? (object-pure? item) (object-constant? item)))
      (if queue?
	  (let ((queue (if pure-space? pure-space-queue constant-space-queue)))
	    (with-absolutely-no-interrupts
	      (lambda ()
		(set-cdr! queue (cons item (cdr queue)))
		unspecific)))
	  (let loop ()
	    (let ((result
		   (purify-internal item
				    pure-space?
				    default-safety-margin)))
	      (cond ((not (pair? result))
		     ;; Wrong phase -- try again.
		     (gc-flip)
		     (loop))
		    ((not (car result))
		     (error "PURIFY: not enough room in constant space"
			    item))))))))

(define (default/stack-overflow)
  (abort->nearest "Aborting!: maximum recursion depth exceeded"))

(define (default/hardware-trap escape-code)
  escape-code
  (abort->nearest "Aborting!: the hardware trapped"))

(define pure-space-queue)
(define constant-space-queue)
(define hook/gc-start)
(define hook/gc-finish)

(define (gc-flip-internal safety-margin)
  (let ((start-value (hook/gc-start)))
    (let ((space-remaining ((ucode-primitive garbage-collect) safety-margin)))
      (gc-finish start-value space-remaining)
      space-remaining)))

(define (purify-internal item pure-space? safety-margin)
  (let ((start-value (hook/gc-start)))
    (let ((result
	   ((ucode-primitive primitive-purify) item
					       pure-space?
					       safety-margin)))
      (if result
	  (gc-finish start-value (cdr result)))
      result)))

(define (default/gc-start)
  #f)

(define (default/gc-finish start-value space-remaining)
  start-value space-remaining
  #f)

(define (gc-finish start-value space-remaining)
  (if (< space-remaining 4096)
      (if gc-boot-loading?
	  (let ((console ((ucode-primitive tty-output-channel 0))))
	    ((ucode-primitive channel-write 4)
	     console
	     gc-boot-death-message
	     0
	     ((ucode-primitive string-length 1) gc-boot-death-message))
	    ((ucode-primitive exit-with-value 1) #x14))
	  (abort->nearest
	   (cmdl-message/append
	    (cmdl-message/strings "Aborting!: out of memory")
	    ;; Clean up whatever possible to avoid a reoccurrence.
	    (cmdl-message/active
	     (lambda (port)
	       port
	       (with-gc-notification! #t gc-clean)))))))
  ((ucode-primitive request-interrupts! 1) interrupt-bit/after-gc)
  (hook/gc-finish start-value space-remaining))

(define gc-boot-loading?)
  
(define gc-boot-death-message
  "\n;; Aborting boot-load: Not enough memory to load -- Use -large option.\n")

;;;; User Primitives

(define (set-gc-safety-margin! #!optional safety-margin)
  (if (not (or (default-object? safety-margin) (not safety-margin)))
      (begin
	(set! default-safety-margin safety-margin)
	(gc-flip safety-margin)))
  default-safety-margin)

(define (gc-flip #!optional safety-margin)
  ;; Optionally overrides the GC safety margin for this flip only.
  (with-absolutely-no-interrupts
   (lambda ()
     (hook/gc-flip (if (default-object? safety-margin)
		       default-safety-margin
		       safety-margin)))))

(define (flush-purification-queue!)
  (if (or (pair? (cdr pure-space-queue))
	  (pair? (cdr constant-space-queue)))
      (begin
	(gc-flip)
	(flush-purification-queue!))))

(define (purify item #!optional pure-space? queue?)
  ;; Purify an item -- move it into pure space and clean everything by
  ;; doing a gc-flip.
  (hook/purify item
	       (if (default-object? pure-space?) #t pure-space?)
	       (if (default-object? queue?) #t queue?))
  item)

(define (constant-space/in-use)
  (let ((v (gc-space-status)))
    (- (vector-ref v 2)
       (vector-ref v 1))))