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	ttrivial-garbage.lisp (15356B)
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	1 ;;;; -- Mode: lisp; indent-tabs-mode: nil --
	2 ;;;
	3 ;;; trivial-garbage.lisp --- Trivial Garbage!
	4 ;;;
	5 ;;; This software is placed in the public domain by Luis Oliveira
	6 ;;; <[email protected]> and is provided with absolutely no
	7 ;;; warranty.
	8
	9 #+xcvb (module ())
	10
	11 (defpackage #:trivial-garbage
	12 (:use #:cl)
	13 (:shadow #:make-hash-table)
	14 (:nicknames #:tg)
	15 (:export #:gc
	16 #:make-weak-pointer
	17 #:weak-pointer-value
	18 #:weak-pointer-p
	19 #:make-weak-hash-table
	20 #:hash-table-weakness
	21 #:finalize
	22 #:cancel-finalization)
	23 (:documentation
	24 "@a[http://common-lisp.net/project/trivial-garbage]{trivial-garbage}
	25 provides a portable API to finalizers, weak hash-tables and weak
	26 pointers on all major implementations of the Common Lisp
	27 programming language. For a good introduction to these
	28 data-structures, have a look at
	29 @a[http://www.haible.de/bruno/papers/cs/weak/WeakDatastructures-writ…
	30 References: Data Types and Implementation} by Bruno Haible.
	31
	32 Source code is available at
	33 @a[https://github.com/trivial-garbage/trivial-garbage]{github},
	34 which you are welcome to use for submitting patches and/or
	35 @a[https://github.com/trivial-garbage/trivial-garbage/issues]{bug
	36 reports}. Discussion takes place on
	37 @a[http://lists.common-lisp.net/cgi-bin/mailman/listinfo/trivial-gar…
	38 at common-lisp.net}.
	39
	40 @a[http://common-lisp.net/project/trivial-garbage/releases/]{Tarball
	41 releases} are available, but the easiest way to install this
	42 library is via @a[http://www.quicklisp.org/]{Quicklisp}:
	43 @code{(ql:quickload :trivial-garbage)}.
	44
	45 @begin[Weak Pointers]{section}
	46 A @em{weak pointer} holds an object in a way that does not prevent
	47 it from being reclaimed by the garbage collector. An object
	48 referenced only by weak pointers is considered unreachable (or
	49 \"weakly reachable\") and so may be collected at any time. When
	50 that happens, the weak pointer's value becomes @code{nil}.
	51
	52 @aboutfun{make-weak-pointer}
	53 @aboutfun{weak-pointer-value}
	54 @aboutfun{weak-pointer-p}
	55 @end{section}
	56
	57 @begin[Weak Hash-Tables]{section}
	58 A @em{weak hash-table} is one that weakly references its keys
	59 and/or values. When both key and value are unreachable (or weakly
	60 reachable) that pair is reclaimed by the garbage collector.
	61
	62 @aboutfun{make-weak-hash-table}
	63 @aboutfun{hash-table-weakness}
	64 @end{section}
	65
	66 @begin[Finalizers]{section}
	67 A @em{finalizer} is a hook that is executed after a given object
	68 has been reclaimed by the garbage collector.
	69
	70 @aboutfun{finalize}
	71 @aboutfun{cancel-finalization}
	72 @end{section}"))
	73
	74 (in-package #:trivial-garbage)
	75
	76 ;;;; GC
	77
	78 (defun gc (&key full verbose)
	79 "Initiates a garbage collection. @code{full} forces the collection
	80 of all generations, when applicable. When @code{verbose} is
	81 @em{true}, diagnostic information about the collection is printed
	82 if possible."
	83 (declare (ignorable verbose full))
	84 #+(or cmu scl) (ext:gc :verbose verbose :full full)
	85 #+sbcl (sb-ext:gc :full full)
	86 #+allegro (excl:gc (not (null full)))
	87 #+(or abcl clisp) (ext:gc)
	88 #+ecl (si:gc t)
	89 #+openmcl (ccl:gc)
	90 #+corman (ccl:gc (if full 3 0))
	91 #+lispworks (hcl:gc-generation (if full t 0))
	92 #+clasp (gctools:garbage-collect))
	93
	94 ;;;; Weak Pointers
	95
	96 #+openmcl
	97 (defvar weak-pointers (cl:make-hash-table :test 'eq :weak :value)
	98 "Weak value hash-table mapping between pseudo weak pointers and its va…
	99
	100 #+(or allegro openmcl lispworks)
	101 (defstruct (weak-pointer (:constructor %make-weak-pointer))
	102 #-openmcl pointer)
	103
	104 (defun make-weak-pointer (object)
	105 "Creates a new weak pointer which points to @code{object}. For
	106 portability reasons, @code{object} must not be @code{nil}."
	107 (assert (not (null object)))
	108 #+sbcl (sb-ext:make-weak-pointer object)
	109 #+(or cmu scl) (ext:make-weak-pointer object)
	110 #+clisp (ext:make-weak-pointer object)
	111 #+abcl (ext:make-weak-reference object)
	112 #+ecl (ext:make-weak-pointer object)
	113 #+allegro
	114 (let ((wv (excl:weak-vector 1)))
	115 (setf (svref wv 0) object)
	116 (%make-weak-pointer :pointer wv))
	117 #+openmcl
	118 (let ((wp (%make-weak-pointer)))
	119 (setf (gethash wp weak-pointers) object)
	120 wp)
	121 #+corman (ccl:make-weak-pointer object)
	122 #+lispworks
	123 (let ((array (make-array 1 :weak t)))
	124 (setf (svref array 0) object)
	125 (%make-weak-pointer :pointer array))
	126 #+clasp (core:make-weak-pointer object))
	127
	128 #-(or allegro openmcl lispworks)
	129 (defun weak-pointer-p (object)
	130 "Returns @em{true} if @code{object} is a weak pointer and @code{nil}
	131 otherwise."
	132 #+sbcl (sb-ext:weak-pointer-p object)
	133 #+(or cmu scl) (ext:weak-pointer-p object)
	134 #+clisp (ext:weak-pointer-p object)
	135 #+abcl (typep object 'ext:weak-reference)
	136 #+ecl (typep object 'ext:weak-pointer)
	137 #+corman (ccl:weak-pointer-p object)
	138 #+clasp (core:weak-pointer-valid object))
	139
	140 (defun weak-pointer-value (weak-pointer)
	141 "If @code{weak-pointer} is valid, returns its value. Otherwise,
	142 returns @code{nil}."
	143 #+sbcl (values (sb-ext:weak-pointer-value weak-pointer))
	144 #+(or cmu scl) (values (ext:weak-pointer-value weak-pointer))
	145 #+clisp (values (ext:weak-pointer-value weak-pointer))
	146 #+abcl (values (ext:weak-reference-value weak-pointer))
	147 #+ecl (values (ext:weak-pointer-value weak-pointer))
	148 #+allegro (svref (weak-pointer-pointer weak-pointer) 0)
	149 #+openmcl (values (gethash weak-pointer weak-pointers))
	150 #+corman (ccl:weak-pointer-obj weak-pointer)
	151 #+lispworks (svref (weak-pointer-pointer weak-pointer) 0)
	152 #+clasp (core:weak-pointer-value weak-pointer))
	153
	154 ;;;; Weak Hash-tables
	155
	156 ;;; Allegro can apparently create weak hash-tables with both weak keys
	157 ;;; and weak values but it's not obvious whether it's an OR or an AND
	158 ;;; relation. TODO: figure that out.
	159
	160 (defun weakness-keyword-arg (weakness)
	161 (declare (ignorable weakness))
	162 #+(or sbcl abcl clasp ecl-weak-hash) :weakness
	163 #+(or clisp openmcl) :weak
	164 #+lispworks :weak-kind
	165 #+allegro (case weakness (:key :weak-keys) (:value :values))
	166 #+cmu :weak-p)
	167
	168 (defvar weakness-warnings '()
	169 "List of weaknesses that have already been warned about this
	170 session. Used by `weakness-missing'.")
	171
	172 (defun weakness-missing (weakness errorp)
	173 "Signal an error or warning, depending on ERRORP, about lack of Lisp
	174 support for WEAKNESS."
	175 (cond (errorp
	176 (error "Your Lisp does not support weak ~(~A~) hash-tables."
	177 weakness))
	178 ((member weakness weakness-warnings) nil)
	179 (t (push weakness weakness-warnings)
	180 (warn "Your Lisp does not support weak ~(~A~) hash-tables."
	181 weakness))))
	182
	183 (defun weakness-keyword-opt (weakness errorp)
	184 (declare (ignorable errorp))
	185 (ecase weakness
	186 (:key
	187 #+(or lispworks sbcl abcl clasp clisp openmcl ecl-weak-hash) :key
	188 #+(or allegro cmu) t
	189 #-(or lispworks sbcl abcl clisp openmcl allegro cmu ecl-weak-hash c…
	190 (weakness-missing weakness errorp))
	191 (:value
	192 #+allegro :weak
	193 #+(or clisp openmcl sbcl abcl lispworks cmu ecl-weak-hash) :value
	194 #-(or allegro clisp openmcl sbcl abcl lispworks cmu ecl-weak-hash c…
	195 (weakness-missing weakness errorp))
	196 (:key-or-value
	197 #+(or clisp sbcl abcl cmu) :key-or-value
	198 #+lispworks :either
	199 #-(or clisp sbcl abcl lispworks cmu clasp)
	200 (weakness-missing weakness errorp))
	201 (:key-and-value
	202 #+(or clisp abcl sbcl cmu ecl-weak-hash) :key-and-value
	203 #+lispworks :both
	204 #-(or clisp sbcl abcl lispworks cmu ecl-weak-hash clasp)
	205 (weakness-missing weakness errorp))))
	206
	207 (defun make-weak-hash-table (&rest args &key weakness (weakness-matters …
	208 #+openmcl (test #'eql)
	209 &allow-other-keys)
	210 "Returns a new weak hash table. In addition to the standard
	211 arguments accepted by @code{cl:make-hash-table}, this function adds
	212 extra keywords: @code{:weakness} being the kind of weak table it
	213 should create, and @code{:weakness-matters} being whether an error
	214 should be signalled when that weakness isn't available (the default
	215 is to signal an error). @code{weakness} can be one of @code{:key},
	216 @code{:value}, @code{:key-or-value}, @code{:key-and-value}.
	217
	218 If @code{weakness} is @code{:key} or @code{:value}, an entry is
	219 kept as long as its key or value is reachable, respectively. If
	220 @code{weakness} is @code{:key-or-value} or @code{:key-and-value},
	221 an entry is kept if either or both of its key and value are
	222 reachable, respectively.
	223
	224 @code{tg::make-hash-table} is available as an alias for this
	225 function should you wish to import it into your package and shadow
	226 @code{cl:make-hash-table}."
	227 (remf args :weakness)
	228 (remf args :weakness-matters)
	229 (if weakness
	230 (let ((arg (weakness-keyword-arg weakness))
	231 (opt (weakness-keyword-opt weakness weakness-matters)))
	232 (apply #'cl:make-hash-table
	233 #+openmcl :test #+openmcl (if (eq opt :key) #'eq test)
	234 (if arg
	235 (list* arg opt args)
	236 args)))
	237 (apply #'cl:make-hash-table args)))
	238
	239 ;;; If you want to use this function to override CL:MAKE-HASH-TABLE,
	240 ;;; it's necessary to shadow-import it. For example:
	241 ;;;
	242 ;;; (defpackage #:foo
	243 ;;; (:use #:common-lisp #:trivial-garbage)
	244 ;;; (:shadowing-import-from #:trivial-garbage #:make-hash-table))
	245 ;;;
	246 (defun make-hash-table (&rest args)
	247 (apply #'make-weak-hash-table args))
	248
	249 (defun hash-table-weakness (ht)
	250 "Returns one of @code{nil}, @code{:key}, @code{:value},
	251 @code{:key-or-value} or @code{:key-and-value}."
	252 #-(or allegro sbcl abcl clisp cmu openmcl lispworks
	253 ecl-weak-hash clasp)
	254 (declare (ignore ht))
	255 ;; keep this first if any of the other lisps bugously insert a NIL
	256 ;; for the returned (values) even when read-suppress is NIL (e.g. cl…
	257 #.(if (find :sbcl features)
	258 (if (find-symbol "HASH-TABLE-WEAKNESS" "SB-EXT")
	259 (read-from-string "(sb-ext:hash-table-weakness ht)")
	260 nil)
	261 (values))
	262 #+abcl (sys:hash-table-weakness ht)
	263 #+ecl-weak-hash (ext:hash-table-weakness ht)
	264 #+allegro (cond ((excl:hash-table-weak-keys ht) :key)
	265 ((eq (excl:hash-table-values ht) :weak) :value))
	266 #+clisp (ext:hash-table-weak-p ht)
	267 #+cmu (let ((weakness (lisp::hash-table-weak-p ht)))
	268 (if (eq t weakness) :key weakness))
	269 #+openmcl (ccl::hash-table-weak-p ht)
	270 #+lispworks (system::hash-table-weak-kind ht)
	271 #+clasp (core:hash-table-weakness ht))
	272
	273 ;;;; Finalizers
	274
	275 ;;; Note: Lispworks can't finalize gensyms.
	276
	277 #+(or allegro clisp lispworks openmcl)
	278 (defvar finalizers
	279 (cl:make-hash-table :test 'eq
	280 #+allegro :weak-keys #+:allegro t
	281 #+(or clisp openmcl) :weak
	282 #+lispworks :weak-kind
	283 #+(or clisp openmcl lispworks) :key
	284 #+clasp :weakness #+clasp :key)
	285 "Weak hashtable that holds registered finalizers.")
	286
	287 #+corman
	288 (progn
	289 (defvar finalizers '()
	290 "Weak alist that holds registered finalizers.")
	291
	292 (defvar finalizers-cs (threads:allocate-critical-section)))
	293
	294 #+lispworks
	295 (progn
	296 (hcl:add-special-free-action 'free-action)
	297 (defun free-action (object)
	298 (let ((finalizers (gethash object finalizers)))
	299 (unless (null finalizers)
	300 (mapc #'funcall finalizers)))))
	301
	302 (defun finalize (object function)
	303 "Pushes a new @code{function} to the @code{object}'s list of
	304 finalizers. @code{function} should take no arguments. Returns
	305 @code{object}.
	306
	307 @b{Note:} @code{function} should not attempt to look at
	308 @code{object} by closing over it because that will prevent it from
	309 being garbage collected."
	310 #+(or cmu scl) (ext:finalize object function)
	311 #+sbcl (sb-ext:finalize object function)
	312 #+abcl (ext:finalize object function)
	313 #+ecl (let ((next-fn (ext:get-finalizer object)))
	314 (ext:set-finalizer
	315 object (lambda (obj)
	316 (declare (ignore obj))
	317 (funcall function)
	318 (when next-fn
	319 (funcall next-fn nil)))))
	320 #+allegro
	321 (progn
	322 (push (excl:schedule-finalization
	323 object (lambda (obj) (declare (ignore obj)) (funcall function…
	324 (gethash object finalizers))
	325 object)
	326 #+clasp (gctools:finalize object function)
	327 #+clisp
	328 ;; The CLISP code used to be a bit simpler but we had to workaround
	329 ;; a bug regarding the interaction between GC and weak hashtables.
	330 ;; See <http://article.gmane.org/gmane.lisp.clisp.general/11028>
	331 ;; and <http://article.gmane.org/gmane.lisp.cffi.devel/994>.
	332 (multiple-value-bind (finalizers presentp)
	333 (gethash object finalizers (cons 'finalizers nil))
	334 (unless presentp
	335 (setf (gethash object finalizers) finalizers)
	336 (ext:finalize object (lambda (obj)
	337 (declare (ignore obj))
	338 (mapc #'funcall (cdr finalizers)))))
	339 (push function (cdr finalizers))
	340 object)
	341 #+openmcl
	342 (progn
	343 (ccl:terminate-when-unreachable
	344 object (lambda (obj) (declare (ignore obj)) (funcall function)))
	345 ;; store number of finalizers
	346 (incf (gethash object finalizers 0))
	347 object)
	348 #+corman
	349 (flet ((get-finalizers (obj)
	350 (assoc obj finalizers :test #'eq :key #'ccl:weak-pointer-ob…
	351 (threads:with-synchronization finalizers-cs
	352 (let ((pair (get-finalizers object)))
	353 (if (null pair)
	354 (push (list (ccl:make-weak-pointer object) function) *finali…
	355 (push function (cdr pair)))))
	356 (ccl:register-finalization
	357 object (lambda (obj)
	358 (threads:with-synchronization finalizers-cs
	359 (mapc #'funcall (cdr (get-finalizers obj)))
	360 (setq finalizers
	361 (delete obj finalizers
	362 :test #'eq :key #'ccl:weak-pointer-obj)))))
	363 object)
	364 #+lispworks
	365 (progn
	366 (let ((finalizers (gethash object finalizers)))
	367 (unless finalizers
	368 (hcl:flag-special-free-action object))
	369 (setf (gethash object finalizers)
	370 (cons function finalizers)))
	371 object))
	372
	373 (defun cancel-finalization (object)
	374 "Cancels all of @code{object}'s finalizers, if any."
	375 #+cmu (ext:cancel-finalization object)
	376 #+scl (ext:cancel-finalization object nil)
	377 #+sbcl (sb-ext:cancel-finalization object)
	378 #+abcl (ext:cancel-finalization object)
	379 #+ecl (ext:set-finalizer object nil)
	380 #+allegro
	381 (progn
	382 (mapc #'excl:unschedule-finalization
	383 (gethash object finalizers))
	384 (remhash object finalizers))
	385 #+clasp (gctools:definalize object)
	386 #+clisp
	387 (multiple-value-bind (finalizers present-p)
	388 (gethash object finalizers)
	389 (when present-p
	390 (setf (cdr finalizers) nil))
	391 (remhash object finalizers))
	392 #+openmcl
	393 (let ((count (gethash object finalizers)))
	394 (unless (null count)
	395 (dotimes (i count)
	396 (ccl:cancel-terminate-when-unreachable object))))
	397 #+corman
	398 (threads:with-synchronization finalizers-cs
	399 (setq finalizers
	400 (delete object finalizers :test #'eq :key #'ccl:weak-pointer…
	401 #+lispworks
	402 (progn
	403 (remhash object finalizers)
	404 (hcl:flag-not-special-free-action object)))