1 ;;;; the basics of the PCL wrapper cache mechanism
3 ;;;; This software is part of the SBCL system. See the README file for
6 ;;;; This software is derived from software originally released by Xerox
7 ;;;; Corporation. Copyright and release statements follow. Later modifications
8 ;;;; to the software are in the public domain and are provided with
9 ;;;; absolutely no warranty. See the COPYING and CREDITS files for more
12 ;;;; copyright information from original PCL sources:
14 ;;;; Copyright (c) 1985, 1986, 1987, 1988, 1989, 1990 Xerox Corporation.
15 ;;;; All rights reserved.
17 ;;;; Use and copying of this software and preparation of derivative works based
18 ;;;; upon this software are permitted. Any distribution of this software or
19 ;;;; derivative works must comply with all applicable United States export
22 ;;;; This software is made available AS IS, and Xerox Corporation makes no
23 ;;;; warranty about the software, its performance or its conformity to any
28 ;;; Ye olde CMUCL comment follows, but it seems likely that the paper
29 ;;; that would be inserted would resemble Kiczales and Rodruigez,
30 ;;; Efficient Method Dispatch in PCL, ACM 1990. Some of the details
31 ;;; changed between that paper and "May Day PCL" of 1992; some other
32 ;;; details have changed since, but reading that paper gives the broad
35 ;;; The caching algorithm implemented:
37 ;;; << put a paper here >>
39 ;;; For now, understand that as far as most of this code goes, a cache
40 ;;; has two important properties. The first is the number of wrappers
41 ;;; used as keys in each cache line. Throughout this code, this value
42 ;;; is always called NKEYS. The second is whether or not the cache
43 ;;; lines of a cache store a value. Throughout this code, this always
46 ;;; Depending on these values, there are three kinds of caches.
48 ;;; NKEYS = 1, VALUEP = NIL
50 ;;; In this kind of cache, each line is 1 word long. No cache locking
51 ;;; is needed since all read's in the cache are a single value.
52 ;;; Nevertheless line 0 (location 0) is reserved, to ensure that
53 ;;; invalid wrappers will not get a first probe hit.
55 ;;; To keep the code simpler, a cache lock count does appear in
56 ;;; location 0 of these caches, that count is incremented whenever
57 ;;; data is written to the cache. But, the actual lookup code (see
58 ;;; make-dlap) doesn't need to do locking when reading the cache.
60 ;;; NKEYS = 1, VALUEP = T
62 ;;; In this kind of cache, each line is 2 words long. Cache locking
63 ;;; must be done to ensure the synchronization of cache reads. Line 0
64 ;;; of the cache (location 0) is reserved for the cache lock count.
65 ;;; Location 1 of the cache is unused (in effect wasted).
69 ;;; In this kind of cache, the 0 word of the cache holds the lock
70 ;;; count. The 1 word of the cache is line 0. Line 0 of these caches
73 ;;; This is done because in this sort of cache, the overhead of doing
74 ;;; the cache probe is high enough that the 1+ required to offset the
75 ;;; location is not a significant cost. In addition, because of the
76 ;;; larger line sizes, the space that would be wasted by reserving
77 ;;; line 0 to hold the lock count is more significant.
81 ;;; A cache is essentially just a vector. The use of the individual
82 ;;; `words' in the vector depends on particular properties of the
83 ;;; cache as described above.
85 ;;; This defines an abstraction for caches in terms of their most
86 ;;; obvious implementation as simple vectors. But, please notice that
87 ;;; part of the implementation of this abstraction, is the function
88 ;;; lap-out-cache-ref. This means that most port-specific
89 ;;; modifications to the implementation of caches will require
90 ;;; corresponding port-specific modifications to the lap code
92 (defmacro cache-vector-ref
(cache-vector location
)
93 `(svref (the simple-vector
,cache-vector
)
94 (sb-ext:truly-the fixnum
,location
)))
96 (defmacro cache-vector-size
(cache-vector)
97 `(array-dimension (the simple-vector
,cache-vector
) 0))
99 (defmacro cache-vector-lock-count
(cache-vector)
100 `(cache-vector-ref ,cache-vector
0))
102 (defun flush-cache-vector-internal (cache-vector)
103 ;; FIXME: To my eye this PCL-LOCK implies we should be holding the
104 ;; lock whenever we play with any cache vector, which doesn't seem
105 ;; to be true. On the other hand that would be too expensive as
106 ;; well, since it would mean serialization across all GFs.
108 (fill (the simple-vector cache-vector
) nil
)
109 (setf (cache-vector-lock-count cache-vector
) 0))
112 ;;; Return an empty cache vector
113 (defun get-cache-vector (size)
114 (declare (type (and unsigned-byte fixnum
) size
))
115 (let ((cv (make-array size
:initial-element nil
)))
116 (setf (cache-vector-lock-count cv
) 0)
119 (defmacro modify-cache
(cache-vector &body body
)
121 ;; This locking scheme is less the sufficient, and not what the
122 ;; PCL implementors had planned: apparently we should increment
123 ;; the lock count atomically, and all cache users should check
124 ;; the count before and after they touch cache: if the counts
125 ;; match the cache was not altered, if they don't match the
126 ;; work needs to be redone.
128 ;; We probably want to re-engineer things so that the whole
129 ;; cache vector gets replaced atomically when we do things
130 ;; to it that could affect others.
131 (multiple-value-prog1
133 (let ((old-count (cache-vector-lock-count ,cache-vector
)))
134 (declare (fixnum old-count
))
135 (setf (cache-vector-lock-count ,cache-vector
)
136 (if (= old-count most-positive-fixnum
)
140 (deftype field-type
()
141 '(mod #.layout-clos-hash-length
))
143 (eval-when (:compile-toplevel
:load-toplevel
:execute
)
144 (declaim (ftype (function (fixnum) (values (and unsigned-byte fixnum
) &optional
))
145 power-of-two-ceiling
))
146 (defun power-of-two-ceiling (x)
147 ;; (expt 2 (ceiling (log x 2)))
148 (ash 1 (integer-length (1- x
)))))
150 ;;; FIXME: We should probably keep just one of these -- or at least use just
152 (declaim (inline compute-line-size
))
153 (defun compute-line-size (x)
154 (power-of-two-ceiling x
))
156 (defconstant +nkeys-limit
+ 256)
158 (defstruct (cache (:constructor make-cache
())
159 (:copier copy-cache-internal
))
161 (nkeys 1 :type
(integer 1 #.
+nkeys-limit
+))
162 (valuep nil
:type
(member nil t
))
163 (nlines 0 :type fixnum
)
164 (field 0 :type field-type
)
165 (limit-fn #'default-limit-fn
:type function
)
166 (mask 0 :type fixnum
)
167 (size 0 :type fixnum
)
168 (line-size 1 :type
(integer 1 #.
(power-of-two-ceiling (1+ +nkeys-limit
+))))
169 (max-location 0 :type fixnum
)
170 (vector #() :type simple-vector
)
171 (overflow nil
:type list
))
173 #-sb-fluid
(declaim (sb-ext:freeze-type cache
))
175 ;;;; wrapper cache numbers
177 ;;; The constant WRAPPER-CACHE-NUMBER-ADDS-OK controls the number of
178 ;;; non-zero bits wrapper cache numbers will have.
180 ;;; The value of this constant is the number of wrapper cache numbers
181 ;;; which can be added and still be certain the result will be a
182 ;;; fixnum. This is used by all the code that computes primary cache
183 ;;; locations from multiple wrappers.
185 ;;; The value of this constant is used to derive the next two which
186 ;;; are the forms of this constant which it is more convenient for the
187 ;;; runtime code to use.
188 (defconstant wrapper-cache-number-length
189 (integer-length layout-clos-hash-max
))
190 (defconstant wrapper-cache-number-mask layout-clos-hash-max
)
191 (defconstant wrapper-cache-number-adds-ok
192 (truncate most-positive-fixnum layout-clos-hash-max
))
194 ;;;; wrappers themselves
196 ;;; This caching algorithm requires that wrappers have more than one
197 ;;; wrapper cache number. You should think of these multiple numbers
198 ;;; as being in columns. That is, for a given cache, the same column
199 ;;; of wrapper cache numbers will be used.
201 ;;; If at some point the cache distribution of a cache gets bad, the
202 ;;; cache can be rehashed by switching to a different column.
204 ;;; The columns are referred to by field number which is that number
205 ;;; which, when used as a second argument to wrapper-ref, will return
206 ;;; that column of wrapper cache number.
208 ;;; This code is written to allow flexibility as to how many wrapper
209 ;;; cache numbers will be in each wrapper, and where they will be
210 ;;; located. It is also set up to allow port specific modifications to
211 ;;; `pack' the wrapper cache numbers on machines where the addressing
212 ;;; modes make that a good idea.
214 ;;; In SBCL, as in CMU CL, we want to do type checking as early as
215 ;;; possible; structures help this. The structures are hard-wired to
216 ;;; have a fixed number of cache hash values, and that number must
217 ;;; correspond to the number of cache lines we use.
218 (defconstant wrapper-cache-number-vector-length
219 layout-clos-hash-length
)
221 (unless (boundp '*the-class-t
*)
222 (setq *the-class-t
* nil
))
224 (defmacro wrapper-class
(wrapper)
225 `(classoid-pcl-class (layout-classoid ,wrapper
)))
226 (defmacro wrapper-no-of-instance-slots
(wrapper)
227 `(layout-length ,wrapper
))
229 ;;; This is called in BRAID when we are making wrappers for classes
230 ;;; whose slots are not initialized yet, and which may be built-in
231 ;;; classes. We pass in the class name in addition to the class.
232 (defun boot-make-wrapper (length name
&optional class
)
233 (let ((found (find-classoid name nil
)))
236 (unless (classoid-pcl-class found
)
237 (setf (classoid-pcl-class found
) class
))
238 (aver (eq (classoid-pcl-class found
) class
))
239 (let ((layout (classoid-layout found
)))
243 (make-wrapper-internal
245 :classoid
(make-standard-classoid
246 :name name
:pcl-class class
))))))
248 ;;; The following variable may be set to a STANDARD-CLASS that has
249 ;;; already been created by the lisp code and which is to be redefined
250 ;;; by PCL. This allows STANDARD-CLASSes to be defined and used for
251 ;;; type testing and dispatch before PCL is loaded.
252 (defvar *pcl-class-boot
* nil
)
254 ;;; In SBCL, as in CMU CL, the layouts (a.k.a wrappers) for built-in
255 ;;; and structure classes already exist when PCL is initialized, so we
256 ;;; don't necessarily always make a wrapper. Also, we help maintain
257 ;;; the mapping between CL:CLASS and SB-KERNEL:CLASSOID objects.
258 (defun make-wrapper (length class
)
260 ((or (typep class
'std-class
)
261 (typep class
'forward-referenced-class
))
262 (make-wrapper-internal
265 (let ((owrap (class-wrapper class
)))
267 (layout-classoid owrap
))
268 ((or (*subtypep
(class-of class
) *the-class-standard-class
*)
269 (*subtypep
(class-of class
) *the-class-funcallable-standard-class
*)
270 (typep class
'forward-referenced-class
))
271 (cond ((and *pcl-class-boot
*
272 (eq (slot-value class
'name
) *pcl-class-boot
*))
273 (let ((found (find-classoid
274 (slot-value class
'name
))))
275 (unless (classoid-pcl-class found
)
276 (setf (classoid-pcl-class found
) class
))
277 (aver (eq (classoid-pcl-class found
) class
))
280 (let ((name (slot-value class
'name
)))
281 (make-standard-classoid :pcl-class class
282 :name
(and (symbolp name
) name
))))))
284 (bug "Got to T branch in ~S" 'make-wrapper
))))))
286 (let* ((found (find-classoid (slot-value class
'name
)))
287 (layout (classoid-layout found
)))
288 (unless (classoid-pcl-class found
)
289 (setf (classoid-pcl-class found
) class
))
290 (aver (eq (classoid-pcl-class found
) class
))
294 (defconstant +first-wrapper-cache-number-index
+ 0)
296 (declaim (inline next-wrapper-cache-number-index
))
297 (defun next-wrapper-cache-number-index (field-number)
298 (and (< field-number
#.
(1- wrapper-cache-number-vector-length
))
301 (declaim (inline wrapper-class
*))
302 (defun wrapper-class* (wrapper)
303 (or (wrapper-class wrapper
)
304 (ensure-non-standard-class
305 (classoid-name (layout-classoid wrapper
)))))
307 ;;; The wrapper cache machinery provides general mechanism for
308 ;;; trapping on the next access to any instance of a given class. This
309 ;;; mechanism is used to implement the updating of instances when the
310 ;;; class is redefined (MAKE-INSTANCES-OBSOLETE). The same mechanism
311 ;;; is also used to update generic function caches when there is a
312 ;;; change to the superclasses of a class.
314 ;;; Basically, a given wrapper can be valid or invalid. If it is
315 ;;; invalid, it means that any attempt to do a wrapper cache lookup
316 ;;; using the wrapper should trap. Also, methods on
317 ;;; SLOT-VALUE-USING-CLASS check the wrapper validity as well. This is
318 ;;; done by calling CHECK-WRAPPER-VALIDITY.
320 (declaim (inline invalid-wrapper-p
))
321 (defun invalid-wrapper-p (wrapper)
322 (not (null (layout-invalid wrapper
))))
324 ;;; We only use this inside INVALIDATE-WRAPPER.
325 (defvar *previous-nwrappers
* (make-hash-table))
327 ;;; We always call this inside WITH-PCL-LOCK.
328 (defun invalidate-wrapper (owrapper state nwrapper
)
329 (aver (member state
'(:flush
:obsolete
) :test
#'eq
))
330 (let ((new-previous ()))
331 ;; First off, a previous call to INVALIDATE-WRAPPER may have
332 ;; recorded OWRAPPER as an NWRAPPER to update to. Since OWRAPPER
333 ;; is about to be invalid, it no longer makes sense to update to
336 ;; We go back and change the previously invalidated wrappers so
337 ;; that they will now update directly to NWRAPPER. This
338 ;; corresponds to a kind of transitivity of wrapper updates.
339 (dolist (previous (gethash owrapper
*previous-nwrappers
*))
340 (when (eq state
:obsolete
)
341 (setf (car previous
) :obsolete
))
342 (setf (cadr previous
) nwrapper
)
343 (push previous new-previous
))
345 ;; FIXME: We are here inside PCL lock, but might someone be
346 ;; accessing the wrapper at the same time from outside the lock?
347 ;; Can it matter that they get 0 from one slot and a valid value
349 (dotimes (i layout-clos-hash-length
)
350 (setf (layout-clos-hash owrapper i
) 0))
352 ;; FIXME: We could save a whopping cons by using (STATE . WRAPPER)
354 (push (setf (layout-invalid owrapper
) (list state nwrapper
))
357 (remhash owrapper
*previous-nwrappers
*)
358 (setf (gethash nwrapper
*previous-nwrappers
*) new-previous
)))
360 (defun check-wrapper-validity (instance)
361 (let* ((owrapper (wrapper-of instance
))
362 (state (layout-invalid owrapper
)))
363 (aver (not (eq state
:uninitialized
)))
366 ;; FIXME: I can't help thinking that, while this does cure the
367 ;; symptoms observed from some class redefinitions, this isn't
368 ;; the place to be doing this flushing. Nevertheless... --
372 ;; We assume in this case, that the :INVALID is from a
373 ;; previous call to REGISTER-LAYOUT for a superclass of
374 ;; INSTANCE's class. See also the comment above
375 ;; FORCE-CACHE-FLUSHES. Paul Dietz has test cases for this.
377 (force-cache-flushes (class-of instance
))
378 (check-wrapper-validity instance
))
382 (flush-cache-trap owrapper
(cadr state
) instance
))
384 (obsolete-instance-trap owrapper
(cadr state
) instance
)))))))
386 (declaim (inline check-obsolete-instance
))
387 (defun check-obsolete-instance (instance)
388 (when (invalid-wrapper-p (layout-of instance
))
389 (check-wrapper-validity instance
)))
392 (defun get-cache (nkeys valuep limit-fn nlines
)
393 (let ((cache (make-cache)))
394 (declare (type cache cache
))
395 (multiple-value-bind (cache-mask actual-size line-size nlines
)
396 (compute-cache-parameters nkeys valuep nlines
)
397 (setf (cache-nkeys cache
) nkeys
398 (cache-valuep cache
) valuep
399 (cache-nlines cache
) nlines
400 (cache-field cache
) +first-wrapper-cache-number-index
+
401 (cache-limit-fn cache
) limit-fn
402 (cache-mask cache
) cache-mask
403 (cache-size cache
) actual-size
404 (cache-line-size cache
) line-size
405 (cache-max-location cache
) (let ((line (1- nlines
)))
408 (1+ (* line line-size
))))
409 (cache-vector cache
) (get-cache-vector actual-size
)
410 (cache-overflow cache
) nil
)
413 (defun get-cache-from-cache (old-cache new-nlines
414 &optional
(new-field +first-wrapper-cache-number-index
+))
415 (let ((nkeys (cache-nkeys old-cache
))
416 (valuep (cache-valuep old-cache
))
417 (cache (make-cache)))
418 (declare (type cache cache
))
419 (multiple-value-bind (cache-mask actual-size line-size nlines
)
420 (if (= new-nlines
(cache-nlines old-cache
))
421 (values (cache-mask old-cache
) (cache-size old-cache
)
422 (cache-line-size old-cache
) (cache-nlines old-cache
))
423 (compute-cache-parameters nkeys valuep new-nlines
))
424 (setf (cache-owner cache
) (cache-owner old-cache
)
425 (cache-nkeys cache
) nkeys
426 (cache-valuep cache
) valuep
427 (cache-nlines cache
) nlines
428 (cache-field cache
) new-field
429 (cache-limit-fn cache
) (cache-limit-fn old-cache
)
430 (cache-mask cache
) cache-mask
431 (cache-size cache
) actual-size
432 (cache-line-size cache
) line-size
433 (cache-max-location cache
) (let ((line (1- nlines
)))
436 (1+ (* line line-size
))))
437 (cache-vector cache
) (get-cache-vector actual-size
)
438 (cache-overflow cache
) nil
)
441 (defun copy-cache (old-cache)
442 (let* ((new-cache (copy-cache-internal old-cache
))
443 (size (cache-size old-cache
))
444 (old-vector (cache-vector old-cache
))
445 (new-vector (get-cache-vector size
)))
446 (declare (simple-vector old-vector new-vector
))
447 (dotimes-fixnum (i size
)
448 (setf (svref new-vector i
) (svref old-vector i
)))
449 (setf (cache-vector new-cache
) new-vector
)
452 (defun compute-cache-parameters (nkeys valuep nlines-or-cache-vector
)
453 ;;(declare (values cache-mask actual-size line-size nlines))
454 (declare (fixnum nkeys
))
456 (let* ((line-size (if valuep
2 1))
457 (cache-size (etypecase nlines-or-cache-vector
460 (power-of-two-ceiling nlines-or-cache-vector
)))
462 (cache-vector-size nlines-or-cache-vector
)))))
463 (declare (type (and unsigned-byte fixnum
) line-size cache-size
))
464 (values (logxor (1- cache-size
) (1- line-size
))
467 (floor cache-size line-size
)))
468 (let* ((line-size (power-of-two-ceiling (if valuep
(1+ nkeys
) nkeys
)))
469 (cache-size (etypecase nlines-or-cache-vector
472 (power-of-two-ceiling nlines-or-cache-vector
)))
474 (1- (cache-vector-size nlines-or-cache-vector
))))))
475 (declare (fixnum line-size cache-size
))
476 (values (logxor (1- cache-size
) (1- line-size
))
479 (floor cache-size line-size
)))))
481 ;;; the various implementations of computing a primary cache location from
482 ;;; wrappers. Because some implementations of this must run fast there are
483 ;;; several implementations of the same algorithm.
485 ;;; The algorithm is:
487 ;;; SUM over the wrapper cache numbers,
488 ;;; ENSURING that the result is a fixnum
489 ;;; MASK the result against the mask argument.
491 ;;; The basic functional version. This is used by the cache miss code to
492 ;;; compute the primary location of an entry.
493 (defun compute-primary-cache-location (field mask wrappers
)
494 (declare (type field-type field
) (fixnum mask
))
495 (if (not (listp wrappers
))
496 (logand mask
(layout-clos-hash wrappers field
))
499 (declare (fixnum location i
))
500 (dolist (wrapper wrappers
)
501 ;; First add the cache number of this wrapper to location.
502 (let ((wrapper-cache-number (layout-clos-hash wrapper field
)))
503 (declare (fixnum wrapper-cache-number
))
504 (if (zerop wrapper-cache-number
)
505 (return-from compute-primary-cache-location
0)
506 (incf location wrapper-cache-number
)))
507 ;; Then, if we are working with lots of wrappers, deal with
508 ;; the wrapper-cache-number-mask stuff.
509 (when (and (not (zerop i
))
510 (zerop (mod i wrapper-cache-number-adds-ok
)))
512 (logand location wrapper-cache-number-mask
)))
514 (1+ (logand mask location
)))))
516 ;;; This version is called on a cache line. It fetches the wrappers
517 ;;; from the cache line and determines the primary location. Various
518 ;;; parts of the cache filling code call this to determine whether it
519 ;;; is appropriate to displace a given cache entry.
521 ;;; If this comes across a wrapper whose CACHE-NO is 0, it returns the
522 ;;; symbol invalid to suggest to its caller that it would be provident
523 ;;; to blow away the cache line in question.
524 (defun compute-primary-cache-location-from-location (to-cache
527 (from-cache to-cache
))
528 (declare (type cache to-cache from-cache
) (fixnum from-location
))
530 (cache-vector (cache-vector from-cache
))
531 (field (cache-field to-cache
))
532 (mask (cache-mask to-cache
))
533 (nkeys (cache-nkeys to-cache
)))
534 (declare (type field-type field
) (fixnum result mask nkeys
)
535 (simple-vector cache-vector
))
536 (dotimes-fixnum (i nkeys
)
537 ;; FIXME: Sometimes we get NIL here as wrapper, apparently because
538 ;; another thread has stomped on the cache-vector.
539 (let* ((wrapper (cache-vector-ref cache-vector
(+ i from-location
)))
540 (wcn (layout-clos-hash wrapper field
)))
541 (declare (fixnum wcn
))
543 (when (and (not (zerop i
))
544 (zerop (mod i wrapper-cache-number-adds-ok
)))
545 (setq result
(logand result wrapper-cache-number-mask
))))
548 (1+ (logand mask result
)))))
550 ;;; NIL: means nothing so far, no actual arg info has NILs in the
553 ;;; CLASS: seen all sorts of metaclasses (specifically, more than one
554 ;;; of the next 5 values) or else have seen something which doesn't
555 ;;; fall into a single category (SLOT-INSTANCE, FORWARD).
557 ;;; T: means everything so far is the class T
558 ;;; STANDARD-INSTANCE: seen only standard classes
559 ;;; BUILT-IN-INSTANCE: seen only built in classes
560 ;;; STRUCTURE-INSTANCE: seen only structure classes
561 ;;; CONDITION-INSTANCE: seen only condition classes
562 (defun raise-metatype (metatype new-specializer
)
563 (let ((slot (find-class 'slot-class
))
564 (standard (find-class 'standard-class
))
565 (fsc (find-class 'funcallable-standard-class
))
566 (condition (find-class 'condition-class
))
567 (structure (find-class 'structure-class
))
568 (built-in (find-class 'built-in-class
))
569 (frc (find-class 'forward-referenced-class
)))
570 (flet ((specializer->metatype
(x)
571 (let ((meta-specializer
572 (if (eq *boot-state
* 'complete
)
573 (class-of (specializer-class x
))
576 ((eq x
*the-class-t
*) t
)
577 ((*subtypep meta-specializer standard
) 'standard-instance
)
578 ((*subtypep meta-specializer fsc
) 'standard-instance
)
579 ((*subtypep meta-specializer condition
) 'condition-instance
)
580 ((*subtypep meta-specializer structure
) 'structure-instance
)
581 ((*subtypep meta-specializer built-in
) 'built-in-instance
)
582 ((*subtypep meta-specializer slot
) 'slot-instance
)
583 ((*subtypep meta-specializer frc
) 'forward
)
584 (t (error "~@<PCL cannot handle the specializer ~S ~
585 (meta-specializer ~S).~@:>"
586 new-specializer meta-specializer
))))))
587 ;; We implement the following table. The notation is
588 ;; that X and Y are distinct meta specializer names.
590 ;; NIL <anything> ===> <anything>
593 (let ((new-metatype (specializer->metatype new-specializer
)))
594 (cond ((eq new-metatype
'slot-instance
) 'class
)
595 ((eq new-metatype
'forward
) 'class
)
596 ((null metatype
) new-metatype
)
597 ((eq metatype new-metatype
) new-metatype
)
600 (defmacro with-dfun-wrappers
((args metatypes
)
601 (dfun-wrappers invalid-wrapper-p
602 &optional wrappers classes types
)
603 invalid-arguments-form
605 `(let* ((args-tail ,args
) (,invalid-wrapper-p nil
) (invalid-arguments-p nil
)
606 (,dfun-wrappers nil
) (dfun-wrappers-tail nil
)
608 `((wrappers-rev nil
) (types-rev nil
) (classes-rev nil
))))
609 (dolist (mt ,metatypes
)
611 (setq invalid-arguments-p t
)
613 (let* ((arg (pop args-tail
))
616 `((class *the-class-t
*)
619 (setq wrapper
(wrapper-of arg
))
620 (when (invalid-wrapper-p wrapper
)
621 (setq ,invalid-wrapper-p t
)
622 (setq wrapper
(check-wrapper-validity arg
)))
623 (cond ((null ,dfun-wrappers
)
624 (setq ,dfun-wrappers wrapper
))
625 ((not (consp ,dfun-wrappers
))
626 (setq dfun-wrappers-tail
(list wrapper
))
627 (setq ,dfun-wrappers
(cons ,dfun-wrappers dfun-wrappers-tail
)))
629 (let ((new-dfun-wrappers-tail (list wrapper
)))
630 (setf (cdr dfun-wrappers-tail
) new-dfun-wrappers-tail
)
631 (setf dfun-wrappers-tail new-dfun-wrappers-tail
))))
633 `((setq class
(wrapper-class* wrapper
))
634 (setq type
`(class-eq ,class
)))))
636 `((push wrapper wrappers-rev
)
637 (push class classes-rev
)
638 (push type types-rev
)))))
639 (if invalid-arguments-p
640 ,invalid-arguments-form
641 (let* (,@(when wrappers
642 `((,wrappers
(nreverse wrappers-rev
))
643 (,classes
(nreverse classes-rev
))
644 (,types
(mapcar (lambda (class)
649 ;;;; some support stuff for getting a hold of symbols that we need when
650 ;;;; building the discriminator codes. It's OK for these to be interned
651 ;;;; symbols because we don't capture any user code in the scope in which
652 ;;;; these symbols are bound.
654 (declaim (list *dfun-arg-symbols
*))
655 (defvar *dfun-arg-symbols
* '(.ARG0. .ARG1. .ARG2. .ARG3.
))
657 (defun dfun-arg-symbol (arg-number)
658 (or (nth arg-number
*dfun-arg-symbols
*)
659 (format-symbol *pcl-package
* ".ARG~A." arg-number
)))
661 (declaim (list *slot-vector-symbols
*))
662 (defvar *slot-vector-symbols
* '(.SLOTS0. .SLOTS1. .SLOTS2. .SLOTS3.
))
664 (defun slot-vector-symbol (arg-number)
665 (or (nth arg-number
*slot-vector-symbols
*)
666 (format-symbol *pcl-package
* ".SLOTS~A." arg-number
)))
668 (declaim (inline make-dfun-required-args
))
669 (defun make-dfun-required-args (metatypes)
670 ;; Micro-optimizations 'R Us
671 (labels ((rec (types i
)
674 (cons (dfun-arg-symbol i
)
675 (rec (cdr types
) (1+ i
))))))
678 (defun make-dfun-lambda-list (metatypes applyp
)
679 (let ((required (make-dfun-required-args metatypes
)))
682 ;; Use &MORE arguments to avoid consing up an &REST list
683 ;; that we might not need at all. See MAKE-EMF-CALL and
684 ;; INVOKE-EFFECTIVE-METHOD-FUNCTION for the other
686 '(&more .dfun-more-context. .dfun-more-count.
))
689 (defun make-dlap-lambda-list (metatypes applyp
)
690 (let* ((required (make-dfun-required-args metatypes
))
691 (lambda-list (if applyp
692 (append required
'(&more .more-context. .more-count.
))
694 ;; Return the full lambda list, the required arguments, a form
695 ;; that will generate a rest-list, and a list of the &MORE
700 '((sb-c::%listify-rest-args
702 (the (and unsigned-byte fixnum
)
705 '(.more-context. .more-count.
)))))
707 (defun make-emf-call (metatypes applyp fn-variable
&optional emf-type
)
708 (let ((required (make-dfun-required-args metatypes
)))
709 `(,(if (eq emf-type
'fast-method-call
)
710 'invoke-effective-method-function-fast
711 'invoke-effective-method-function
)
714 :required-args
,required
715 ;; INVOKE-EFFECTIVE-METHOD-FUNCTION will decide whether to use
716 ;; the :REST-ARG version or the :MORE-ARG version depending on
717 ;; the type of the EMF.
718 :rest-arg
,(if applyp
719 ;; Creates a list from the &MORE arguments.
720 '((sb-c::%listify-rest-args
722 (the (and unsigned-byte fixnum
)
725 :more-arg
,(when applyp
726 '(.dfun-more-context. .dfun-more-count.
)))))
728 (defun make-fast-method-call-lambda-list (metatypes applyp
)
729 (list* '.pv-cell.
'.next-method-call.
730 (make-dfun-lambda-list metatypes applyp
)))
733 (defmacro with-local-cache-functions
((cache) &body body
)
734 `(let ((.cache.
,cache
))
735 (declare (type cache .cache.
))
736 (labels ((cache () .cache.
)
737 (nkeys () (cache-nkeys .cache.
))
738 (line-size () (cache-line-size .cache.
))
739 (c-vector () (cache-vector .cache.
))
740 (valuep () (cache-valuep .cache.
))
741 (nlines () (cache-nlines .cache.
))
742 (max-location () (cache-max-location .cache.
))
743 (limit-fn () (cache-limit-fn .cache.
))
744 (size () (cache-size .cache.
))
745 (mask () (cache-mask .cache.
))
746 (field () (cache-field .cache.
))
747 (overflow () (cache-overflow .cache.
))
749 ;; Return T IFF this cache location is reserved. The
750 ;; only time this is true is for line number 0 of an
753 (line-reserved-p (line)
754 (declare (fixnum line
))
758 (location-reserved-p (location)
759 (declare (fixnum location
))
763 ;; Given a line number, return the cache location.
764 ;; This is the value that is the second argument to
765 ;; cache-vector-ref. Basically, this deals with the
766 ;; offset of nkeys>1 caches and multiplies by line
769 (line-location (line)
770 (declare (fixnum line
))
771 (when (line-reserved-p line
)
772 (error "line is reserved"))
774 (the fixnum
(* line
(line-size)))
775 (the fixnum
(1+ (the fixnum
(* line
(line-size)))))))
777 ;; Given a cache location, return the line. This is
778 ;; the inverse of LINE-LOCATION.
780 (location-line (location)
781 (declare (fixnum location
))
783 (floor location
(line-size))
784 (floor (the fixnum
(1- location
)) (line-size))))
786 ;; Given a line number, return the wrappers stored at
787 ;; that line. As usual, if nkeys=1, this returns a
788 ;; single value. Only when nkeys>1 does it return a
789 ;; list. An error is signalled if the line is
792 (line-wrappers (line)
793 (declare (fixnum line
))
794 (when (line-reserved-p line
) (error "Line is reserved."))
795 (location-wrappers (line-location line
)))
797 (location-wrappers (location) ; avoid multiplies caused by line-location
798 (declare (fixnum location
))
800 (cache-vector-ref (c-vector) location
)
801 (let ((list (make-list (nkeys)))
803 (declare (simple-vector vector
))
804 (dotimes (i (nkeys) list
)
807 (cache-vector-ref vector
(+ location i
)))))))
809 ;; Given a line number, return true IFF the line's
810 ;; wrappers are the same as wrappers.
812 (line-matches-wrappers-p (line wrappers
)
813 (declare (fixnum line
))
814 (and (not (line-reserved-p line
))
815 (location-matches-wrappers-p (line-location line
)
818 (location-matches-wrappers-p (loc wrappers
) ; must not be reserved
819 (declare (fixnum loc
))
820 (let ((cache-vector (c-vector)))
821 (declare (simple-vector cache-vector
))
823 (eq wrappers
(cache-vector-ref cache-vector loc
))
824 (dotimes (i (nkeys) t
)
826 (unless (eq (pop wrappers
)
827 (cache-vector-ref cache-vector
(+ loc i
)))
830 ;; Given a line number, return the value stored at that line.
831 ;; If valuep is NIL, this returns NIL. As with line-wrappers,
832 ;; an error is signalled if the line is reserved.
835 (declare (fixnum line
))
836 (when (line-reserved-p line
) (error "Line is reserved."))
837 (location-value (line-location line
)))
839 (location-value (loc)
840 (declare (fixnum loc
))
842 (cache-vector-ref (c-vector) (+ loc
(nkeys)))))
844 ;; Given a line number, return true IFF that line has data in
845 ;; it. The state of the wrappers stored in the line is not
846 ;; checked. An error is signalled if line is reserved.
848 (when (line-reserved-p line
) (error "Line is reserved."))
849 (not (null (cache-vector-ref (c-vector) (line-location line
)))))
851 ;; Given a line number, return true IFF the line is full and
852 ;; there are no invalid wrappers in the line, and the line's
853 ;; wrappers are different from wrappers.
854 ;; An error is signalled if the line is reserved.
856 (line-valid-p (line wrappers
)
857 (declare (fixnum line
))
858 (when (line-reserved-p line
) (error "Line is reserved."))
859 (location-valid-p (line-location line
) wrappers
))
861 (location-valid-p (loc wrappers
)
862 (declare (fixnum loc
))
863 (let ((cache-vector (c-vector))
864 (wrappers-mismatch-p (null wrappers
)))
865 (declare (simple-vector cache-vector
))
866 (dotimes (i (nkeys) wrappers-mismatch-p
)
868 (let ((wrapper (cache-vector-ref cache-vector
(+ loc i
))))
869 (when (or (null wrapper
)
870 (invalid-wrapper-p wrapper
))
872 (unless (and wrappers
877 (setq wrappers-mismatch-p t
))))))
879 ;; How many unreserved lines separate line-1 and line-2.
881 (line-separation (line-1 line-2
)
882 (declare (fixnum line-1 line-2
))
883 (let ((diff (the fixnum
(- line-2 line-1
))))
884 (declare (fixnum diff
))
886 (setq diff
(+ diff
(nlines)))
887 (when (line-reserved-p 0)
888 (setq diff
(1- diff
))))
891 ;; Given a cache line, get the next cache line. This will not
892 ;; return a reserved line.
895 (declare (fixnum line
))
896 (if (= line
(the fixnum
(1- (nlines))))
897 (if (line-reserved-p 0) 1 0)
898 (the fixnum
(1+ line
))))
901 (declare (fixnum loc
))
902 (if (= loc
(max-location))
906 (the fixnum
(+ loc
(line-size)))))
908 ;; Given a line which has a valid entry in it, this
909 ;; will return the primary cache line of the wrappers
910 ;; in that line. We just call
911 ;; COMPUTE-PRIMARY-CACHE-LOCATION-FROM-LOCATION, this
912 ;; is an easier packaging up of the call to it.
915 (declare (fixnum line
))
916 (location-line (line-primary-location line
)))
918 (line-primary-location (line)
919 (declare (fixnum line
))
920 (compute-primary-cache-location-from-location
921 (cache) (line-location line
))))
922 (declare (ignorable #'cache
#'nkeys
#'line-size
#'c-vector
#'valuep
923 #'nlines
#'max-location
#'limit-fn
#'size
924 #'mask
#'field
#'overflow
#'line-reserved-p
925 #'location-reserved-p
#'line-location
926 #'location-line
#'line-wrappers
#'location-wrappers
927 #'line-matches-wrappers-p
928 #'location-matches-wrappers-p
929 #'line-value
#'location-value
#'line-full-p
930 #'line-valid-p
#'location-valid-p
931 #'line-separation
#'next-line
#'next-location
932 #'line-primary
#'line-primary-location
))
935 ;;; Here is where we actually fill, recache and expand caches.
937 ;;; The functions FILL-CACHE and PROBE-CACHE are the ONLY external
938 ;;; entrypoints into this code.
940 ;;; FILL-CACHE returns 1 value: a new cache
942 ;;; a wrapper field number
945 ;;; an absolute cache size (the size of the actual vector)
946 ;;; It tries to re-adjust the cache every time it makes a new fill.
947 ;;; The intuition here is that we want uniformity in the number of
948 ;;; probes needed to find an entry. Furthermore, adjusting has the
949 ;;; nice property of throwing out any entries that are invalid.
950 (defvar *cache-expand-threshold
* 1.25)
952 (defun fill-cache (cache wrappers value
)
953 ;; FILL-CACHE won't return if WRAPPERS is nil, might as well check..
955 (or (fill-cache-p nil cache wrappers value
)
956 (and (< (ceiling (* (cache-count cache
) *cache-expand-threshold
*))
957 (if (= (cache-nkeys cache
) 1)
958 (1- (cache-nlines cache
))
959 (cache-nlines cache
)))
960 (adjust-cache cache wrappers value
))
961 (expand-cache cache wrappers value
)))
963 (defvar *check-cache-p
* nil
)
965 (defmacro maybe-check-cache
(cache)
967 (when *check-cache-p
*
968 (check-cache ,cache
))
971 (defun check-cache (cache)
972 (with-local-cache-functions (cache)
973 (let ((location (if (= (nkeys) 1) 0 1))
974 (limit (funcall (limit-fn) (nlines))))
975 (dotimes-fixnum (i (nlines) cache
)
976 (when (and (not (location-reserved-p location
))
978 (let* ((home-loc (compute-primary-cache-location-from-location
980 (home (location-line (if (location-reserved-p home-loc
)
981 (next-location home-loc
)
983 (sep (when home
(line-separation home i
))))
984 (when (and sep
(> sep limit
))
985 (error "bad cache ~S ~@
986 value at location ~W: ~W lines from its home. The limit is ~W."
987 cache location sep limit
))))
988 (setq location
(next-location location
))))))
990 (defun probe-cache (cache wrappers
&optional default limit-fn
)
992 (with-local-cache-functions (cache)
993 (let* ((location (compute-primary-cache-location (field) (mask) wrappers
))
994 (limit (funcall (or limit-fn
(limit-fn)) (nlines))))
995 (declare (fixnum location limit
))
996 (when (location-reserved-p location
)
997 (setq location
(next-location location
)))
998 (dotimes-fixnum (i (1+ limit
))
999 (when (location-matches-wrappers-p location wrappers
)
1000 (return-from probe-cache
(or (not (valuep))
1001 (location-value location
))))
1002 (setq location
(next-location location
)))
1003 (dolist (entry (overflow))
1004 (when (equal (car entry
) wrappers
)
1005 (return-from probe-cache
(or (not (valuep))
1009 (defun map-cache (function cache
&optional set-p
)
1010 (with-local-cache-functions (cache)
1011 (let ((set-p (and set-p
(valuep))))
1012 (dotimes-fixnum (i (nlines) cache
)
1013 (unless (or (line-reserved-p i
) (not (line-valid-p i nil
)))
1014 (let ((value (funcall function
(line-wrappers i
) (line-value i
))))
1016 ;; FIXME: Cache modification: should we not be holding a lock?
1017 (setf (cache-vector-ref (c-vector) (+ (line-location i
) (nkeys)))
1019 (dolist (entry (overflow))
1020 (let ((value (funcall function
(car entry
) (cdr entry
))))
1022 (setf (cdr entry
) value
))))))
1025 (defun cache-count (cache)
1026 (with-local-cache-functions (cache)
1028 (declare (fixnum count
))
1029 (dotimes-fixnum (i (nlines) count
)
1030 (unless (line-reserved-p i
)
1031 (when (line-full-p i
)
1034 (defun entry-in-cache-p (cache wrappers value
)
1035 (declare (ignore value
))
1036 (with-local-cache-functions (cache)
1037 (dotimes-fixnum (i (nlines))
1038 (unless (line-reserved-p i
)
1039 (when (equal (line-wrappers i
) wrappers
)
1042 ;;; returns T or NIL
1044 ;;; FIXME: Deceptive name as this has side-effects.
1045 (defun fill-cache-p (forcep cache wrappers value
)
1046 (with-local-cache-functions (cache)
1047 (let* ((location (compute-primary-cache-location (field) (mask) wrappers
))
1048 (primary (location-line location
)))
1049 (declare (fixnum location primary
))
1050 ;; FIXME: I tried (aver (> location 0)) and (aver (not
1051 ;; (location-reserved-p location))) here, on the basis that
1052 ;; particularly passing a LOCATION of 0 for a cache with more
1053 ;; than one key would cause PRIMARY to be -1. However, the
1054 ;; AVERs triggered during the bootstrap, and removing them
1055 ;; didn't cause anything to break, so I've left them removed.
1056 ;; I'm still confused as to what is right. -- CSR, 2006-04-20
1057 (multiple-value-bind (free emptyp
)
1058 (find-free-cache-line primary cache wrappers
)
1059 (when (or forcep emptyp
)
1061 (push (cons (line-wrappers free
) (line-value free
))
1062 (cache-overflow cache
)))
1063 ;; (fill-line free wrappers value)
1065 (declare (fixnum line
))
1066 (when (line-reserved-p line
)
1067 (error "attempt to fill a reserved line"))
1068 (let ((loc (line-location line
))
1069 (cache-vector (c-vector)))
1070 (declare (fixnum loc
) (simple-vector cache-vector
))
1071 ;; FIXME: Cache modifications: should we not be holding
1073 (cond ((= (nkeys) 1)
1074 (setf (cache-vector-ref cache-vector loc
) wrappers
)
1076 (setf (cache-vector-ref cache-vector
(1+ loc
)) value
)))
1079 (declare (fixnum i
))
1080 (dolist (w wrappers
)
1081 (setf (cache-vector-ref cache-vector
(+ loc i
)) w
)
1082 (setq i
(the fixnum
(1+ i
)))))
1084 (setf (cache-vector-ref cache-vector
(+ loc
(nkeys)))
1086 (maybe-check-cache cache
))))))))
1088 ;;; FIXME: Deceptive name as this has side-effects
1089 (defun fill-cache-from-cache-p (forcep cache from-cache from-line
)
1090 (declare (fixnum from-line
))
1091 (with-local-cache-functions (cache)
1092 (let ((primary (location-line
1093 (compute-primary-cache-location-from-location
1094 cache
(line-location from-line
) from-cache
))))
1095 (declare (fixnum primary
))
1096 (multiple-value-bind (free emptyp
)
1097 (find-free-cache-line primary cache
)
1098 (when (or forcep emptyp
)
1100 (push (cons (line-wrappers free
) (line-value free
))
1101 (cache-overflow cache
)))
1102 ;;(transfer-line from-cache-vector from-line cache-vector free)
1103 (let ((from-cache-vector (cache-vector from-cache
))
1104 (to-cache-vector (c-vector))
1106 (declare (fixnum to-line
))
1107 (if (line-reserved-p to-line
)
1108 (error "transferring something into a reserved cache line")
1109 (let ((from-loc (line-location from-line
))
1110 (to-loc (line-location to-line
)))
1111 (declare (fixnum from-loc to-loc
))
1112 (modify-cache to-cache-vector
1113 (dotimes-fixnum (i (line-size))
1114 (setf (cache-vector-ref to-cache-vector
1116 (cache-vector-ref from-cache-vector
1117 (+ from-loc i
)))))))
1118 (maybe-check-cache cache
)))))))
1120 ;;; Returns NIL or (values <field> <cache-vector>)
1122 ;;; This is only called when it isn't possible to put the entry in the
1123 ;;; cache the easy way. That is, this function assumes that
1124 ;;; FILL-CACHE-P has been called as returned NIL.
1126 ;;; If this returns NIL, it means that it wasn't possible to find a
1127 ;;; wrapper field for which all of the entries could be put in the
1128 ;;; cache (within the limit).
1129 (defun adjust-cache (cache wrappers value
)
1130 (with-local-cache-functions (cache)
1131 (let ((ncache (get-cache-from-cache cache
(nlines) (field))))
1132 (do ((nfield (cache-field ncache
)
1133 (next-wrapper-cache-number-index nfield
)))
1135 (setf (cache-field ncache
) nfield
)
1136 (labels ((try-one-fill-from-line (line)
1137 (fill-cache-from-cache-p nil ncache cache line
))
1138 (try-one-fill (wrappers value
)
1139 (fill-cache-p nil ncache wrappers value
)))
1140 (if (and (dotimes-fixnum (i (nlines) t
)
1141 (when (and (null (line-reserved-p i
))
1142 (line-valid-p i wrappers
))
1143 (unless (try-one-fill-from-line i
) (return nil
))))
1144 (dolist (wrappers+value
(cache-overflow cache
) t
)
1145 (unless (try-one-fill (car wrappers
+value
) (cdr wrappers
+value
))
1147 (try-one-fill wrappers value
))
1148 (return (maybe-check-cache ncache
))
1149 (flush-cache-vector-internal (cache-vector ncache
))))))))
1151 ;;; returns: (values <cache>)
1152 (defun expand-cache (cache wrappers value
)
1153 ;;(declare (values cache))
1154 (with-local-cache-functions (cache)
1155 (let ((ncache (get-cache-from-cache cache
(* (nlines) 2))))
1156 (labels ((do-one-fill-from-line (line)
1157 (unless (fill-cache-from-cache-p nil ncache cache line
)
1158 (do-one-fill (line-wrappers line
) (line-value line
))))
1159 (do-one-fill (wrappers value
)
1160 (setq ncache
(or (adjust-cache ncache wrappers value
)
1161 (fill-cache-p t ncache wrappers value
))))
1162 (try-one-fill (wrappers value
)
1163 (fill-cache-p nil ncache wrappers value
)))
1164 (dotimes-fixnum (i (nlines))
1165 (when (and (null (line-reserved-p i
))
1166 (line-valid-p i wrappers
))
1167 (do-one-fill-from-line i
)))
1168 (dolist (wrappers+value
(cache-overflow cache
))
1169 (unless (try-one-fill (car wrappers
+value
) (cdr wrappers
+value
))
1170 (do-one-fill (car wrappers
+value
) (cdr wrappers
+value
))))
1171 (unless (try-one-fill wrappers value
)
1172 (do-one-fill wrappers value
))
1173 (maybe-check-cache ncache
)))))
1175 (defvar *pcl-misc-random-state
* (make-random-state))
1177 ;;; This is the heart of the cache filling mechanism. It implements
1178 ;;; the decisions about where entries are placed.
1180 ;;; Find a line in the cache at which a new entry can be inserted.
1183 ;;; <empty?> is <line> in fact empty?
1184 (defun find-free-cache-line (primary cache
&optional wrappers
)
1185 ;;(declare (values line empty?))
1186 (declare (fixnum primary
))
1187 (with-local-cache-functions (cache)
1188 (when (line-reserved-p primary
) (setq primary
(next-line primary
)))
1189 (let ((limit (funcall (limit-fn) (nlines)))
1192 (p primary
) (s primary
))
1193 (declare (fixnum p s limit
))
1196 ;; Try to find a free line starting at <s>. <p> is the
1197 ;; primary line of the entry we are finding a free
1198 ;; line for, it is used to compute the separations.
1199 (do* ((line s
(next-line line
))
1200 (nsep (line-separation p s
) (1+ nsep
)))
1202 (declare (fixnum line nsep
))
1203 (when (null (line-valid-p line wrappers
)) ;If this line is empty or
1204 (push line lines
) ;invalid, just use it.
1205 (return-from find-free
))
1206 (when (and wrappedp
(>= line primary
))
1207 ;; have gone all the way around the cache, time to quit
1208 (return-from find-free-cache-line
(values primary nil
)))
1209 (let ((osep (line-separation (line-primary line
) line
)))
1210 (when (>= osep limit
)
1211 (return-from find-free-cache-line
(values primary nil
)))
1212 (when (cond ((= nsep limit
) t
)
1214 (zerop (random 2 *pcl-misc-random-state
*)))
1217 ;; See whether we can displace what is in this line so that we
1218 ;; can use the line.
1219 (when (= line
(the fixnum
(1- (nlines)))) (setq wrappedp t
))
1220 (setq p
(line-primary line
))
1221 (setq s
(next-line line
))
1224 (when (= line
(the fixnum
(1- (nlines)))) (setq wrappedp t
)))))
1225 ;; Do all the displacing.
1227 (when (null (cdr lines
)) (return nil
))
1228 (let ((dline (pop lines
))
1230 (declare (fixnum dline line
))
1231 ;;Copy from line to dline (dline is known to be free).
1232 (let ((from-loc (line-location line
))
1233 (to-loc (line-location dline
))
1234 (cache-vector (c-vector)))
1235 (declare (fixnum from-loc to-loc
) (simple-vector cache-vector
))
1236 (modify-cache cache-vector
1237 (dotimes-fixnum (i (line-size))
1238 (setf (cache-vector-ref cache-vector
1240 (cache-vector-ref cache-vector
1242 (setf (cache-vector-ref cache-vector
1245 (values (car lines
) t
))))
1247 (defun default-limit-fn (nlines)