Language/OS - Multiplatform Resource Library/LANGUAGE OS.iso/pcl/sptmbr16.lha/cache.lisp

Text File | 1992-12-21 | 51.2 KB | 1,485 lines

;;;-*-Mode:LISP; Package:(PCL LISP 1000); Base:10; Syntax:Common-lisp -*-
;;;
;;; *************************************************************************
;;; Copyright (c) 1985, 1986, 1987, 1988, 1989, 1990 Xerox Corporation.
;;; All rights reserved.
;;;
;;; Use and copying of this software and preparation of derivative works
;;; based upon this software are permitted.  Any distribution of this
;;; software or derivative works must comply with all applicable United
;;; States export control laws.
;;;
;;; This software is made available AS IS, and Xerox Corporation makes no
;;; warranty about the software, its performance or its conformity to any
;;; specification.
;;;
;;; Any person obtaining a copy of this software is requested to send their
;;; name and post office or electronic mail address to:
;;;   CommonLoops Coordinator
;;;   Xerox PARC
;;;   3333 Coyote Hill Rd.
;;;   Palo Alto, CA 94304
;;; (or send Arpanet mail to [e-mail])
;;;
;;; Suggestions, comments and requests for improvements are also welcome.
;;; *************************************************************************
;;;
;;; The basics of the PCL wrapper cache mechanism.
;;;

(in-package :pcl)
;;;
;;; The caching algorithm implemented:
;;;
;;; << put a paper here >>
;;;
;;; For now, understand that as far as most of this code goes, a cache has
;;; two important properties.  The first is the number of wrappers used as
;;; keys in each cache line.  Throughout this code, this value is always
;;; called NKEYS.  The second is whether or not the cache lines of a cache
;;; store a value.  Throughout this code, this always called VALUEP.
;;;
;;; Depending on these values, there are three kinds of caches.
;;;
;;; NKEYS = 1, VALUEP = NIL
;;;
;;; In this kind of cache, each line is 1 word long.  No cache locking is
;;; needed since all read's in the cache are a single value.  Nevertheless
;;; line 0 (location 0) is reserved, to ensure that invalid wrappers will
;;; not get a first probe hit.
;;;
;;; To keep the code simpler, a cache lock count does appear in location 0
;;; of these caches, that count is incremented whenever data is written to
;;; the cache.  But, the actual lookup code (see make-dlap) doesn't need to
;;; do locking when reading the cache.
;;;
;;;
;;; NKEYS = 1, VALUEP = T
;;;
;;; In this kind of cache, each line is 2 words long.  Cache locking must
;;; be done to ensure the synchronization of cache reads.  Line 0 of the
;;; cache (location 0) is reserved for the cache lock count.  Location 1
;;; of the cache is unused (in effect wasted).
;;;
;;; NKEYS > 1
;;;
;;; In this kind of cache, the 0 word of the cache holds the lock count.
;;; The 1 word of the cache is line 0.  Line 0 of these caches is not
;;; reserved.
;;;
;;; This is done because in this sort of cache, the overhead of doing the
;;; cache probe is high enough that the 1+ required to offset the location
;;; is not a significant cost.  In addition, because of the larger line
;;; sizes, the space that would be wasted by reserving line 0 to hold the
;;; lock count is more significant.
;;;

;;;
;;; Caches
;;;
;;; A cache is essentially just a vector.  The use of the individual `words'
;;; in the vector depends on particular properties of the cache as described
;;; above.
;;;
;;; This defines an abstraction for caches in terms of their most obvious
;;; implementation as simple vectors.  But, please notice that part of the
;;; implementation of this abstraction, is the function lap-out-cache-ref.
;;; This means that most port-specific modifications to the implementation
;;; of caches will require corresponding port-specific modifications to the
;;; lap code assembler.
;;;
(defmacro cache-vector-ref (cache-vector location)
  `(svref (the simple-vector ,cache-vector)
          (#-cmu the #+cmu ext:truly-the fixnum ,location)))

(defmacro cache-vector-size (cache-vector)
  `(array-dimension (the simple-vector ,cache-vector) 0))

(defun allocate-cache-vector (size)
  (make-array size :adjustable nil))

(defmacro cache-vector-lock-count (cache-vector)
  `(cache-vector-ref ,cache-vector 0))

(defun flush-cache-vector-internal (cache-vector)
  (without-interrupts
    (fill (the simple-vector cache-vector) nil)
    (setf (cache-vector-lock-count cache-vector) 0))
  cache-vector)

(defmacro modify-cache (cache-vector &body body)
  `(without-interrupts
     (multiple-value-prog1
       (progn ,@body)
       (let ((old-count (cache-vector-lock-count ,cache-vector)))
     (declare (fixnum old-count))
     (setf (cache-vector-lock-count ,cache-vector)
           (if (= old-count most-positive-fixnum)
           1 (the fixnum (1+ old-count))))))))

(deftype field-type ()
  '(integer 0    ;#.(position 'number wrapper-layout)
            7))  ;#.(position 'number wrapper-layout :from-end t)

(eval-when (compile load eval)
(defun power-of-two-ceiling (x)
  (declare (fixnum x))
  ;;(expt 2 (ceiling (log x 2)))
  (the fixnum (ash 1 (integer-length (1- x)))))

(defconstant *nkeys-limit* 256)
)

(defstruct (cache
         (:print-function print-cache)
         (:constructor make-cache ())
         (:copier copy-cache-internal))
  (owner nil)
  (nkeys 1 :type (integer 1 #.*nkeys-limit*))
  (valuep nil :type (member nil t))
  (nlines 0 :type fixnum)
  (field 0 :type field-type)
  (limit-fn #'default-limit-fn :type function)
  (mask 0 :type fixnum)
  (size 0 :type fixnum)
  (line-size 1 :type (integer 1 #.(power-of-two-ceiling (1+ *nkeys-limit*))))
  (max-location 0 :type fixnum)
  (vector #() :type simple-vector)
  (overflow nil :type list))

(defun print-cache (cache stream depth)
  (declare (ignore depth))
  (printing-random-thing (cache stream)
    (format stream "cache ~D ~S ~D"
        (cache-nkeys cache) (cache-valuep cache) (cache-nlines cache))))

#+akcl
(si::freeze-defstruct 'cache)

(defmacro cache-lock-count (cache)
  `(cache-vector-lock-count (cache-vector ,cache)))


;;;
;;; Some facilities for allocation and freeing caches as they are needed.
;;; This is done on the assumption that a better port of PCL will arrange
;;; to cons these all the same static area.  Given that, the fact that
;;; PCL tries to reuse them should be a win.
;;;
(defvar *free-cache-vectors* (make-hash-table :size 16 :test 'eql))

;;;
;;; Return a cache that has had flush-cache-vector-internal called on it.  This
;;; returns a cache of exactly the size requested, it won't ever return a
;;; larger cache.
;;;
(defun get-cache-vector (size)
  (let ((entry (gethash size *free-cache-vectors*)))
    (without-interrupts
      (cond ((null entry)
         (setf (gethash size *free-cache-vectors*) (cons 0 nil))
         (get-cache-vector size))
        ((null (cdr entry))
         (incf (car entry))
         (flush-cache-vector-internal (allocate-cache-vector size)))
        (t
         (let ((cache (cdr entry)))
           (setf (cdr entry) (cache-vector-ref cache 0))
           (flush-cache-vector-internal cache)))))))

(defun free-cache-vector (cache-vector)
  (let ((entry (gethash (cache-vector-size cache-vector) *free-cache-vectors*)))
    (without-interrupts
      (if (null entry)
      (error "Attempt to free a cache-vector not allocated by GET-CACHE-VECTOR.")
      (let ((thread (cdr entry)))
        (loop (unless thread (return))
          (when (eq thread cache-vector) (error "Freeing a cache twice."))
          (setq thread (cache-vector-ref thread 0)))
        (flush-cache-vector-internal cache-vector)        ;Help the GC
        (setf (cache-vector-ref cache-vector 0) (cdr entry))
        (setf (cdr entry) cache-vector)
        nil)))))

;;;
;;; This is just for debugging and analysis.  It shows the state of the free
;;; cache resource.
;;;
(defun show-free-cache-vectors ()
  (let ((elements ()))
    (maphash #'(lambda (s e) (push (list s e) elements)) *free-cache-vectors*)
    (setq elements (sort elements #'< :key #'car))
    (dolist (e elements)
      (let* ((size (car e))
         (entry (cadr e))
         (allocated (car entry))
         (head (cdr entry))
         (free 0))
    (loop (when (null head) (return t))
          (setq head (cache-vector-ref head 0))
          (incf free))
    (format t
        "~&There  ~4D are caches of size ~4D. (~D free  ~3D%)"
        allocated
        size
        free
        (floor (* 100 (/ free (float allocated)))))))))


;;;
;;; Wrapper cache numbers
;;;

;;;
;;; The constant WRAPPER-CACHE-NUMBER-ADDS-OK controls the number of non-zero
;;; bits wrapper cache numbers will have.
;;;
;;; The value of this constant is the number of wrapper cache numbers which
;;; can be added and still be certain the result will be a fixnum.  This is
;;; used by all the code that computes primary cache locations from multiple
;;; wrappers.
;;;
;;; The value of this constant is used to derive the next two which are the
;;; forms of this constant which it is more convenient for the runtime code
;;; to use.
;;;
(eval-when (compile load eval)

(defconstant wrapper-cache-number-adds-ok 4)

(defconstant wrapper-cache-number-length
         (- (integer-length most-positive-fixnum)
        wrapper-cache-number-adds-ok))

(defconstant wrapper-cache-number-mask
         (1- (expt 2 wrapper-cache-number-length)))


(defvar *get-wrapper-cache-number* (make-random-state))

(defun get-wrapper-cache-number ()
  (let ((n 0))
    (declare (fixnum n))
    (loop
      (setq n
        (logand wrapper-cache-number-mask
            (random most-positive-fixnum *get-wrapper-cache-number*)))
      (unless (zerop n) (return n)))))


(unless (> wrapper-cache-number-length 8)
  (error "In this implementation of Common Lisp, fixnums are so small that~@
          wrapper cache numbers end up being only ~D bits long.  This does~@
          not actually keep PCL from running, but it may degrade cache~@
          performance.~@
          You may want to consider changing the value of the constant~@
          WRAPPER-CACHE-NUMBER-ADDS-OK.")))


;;;
;;; wrappers themselves
;;;
;;; This caching algorithm requires that wrappers have more than one wrapper
;;; cache number.  You should think of these multiple numbers as being in
;;; columns.  That is, for a given cache, the same column of wrapper cache
;;; numbers will be used.
;;;
;;; If at some point the cache distribution of a cache gets bad, the cache
;;; can be rehashed by switching to a different column.
;;;
;;; The columns are referred to by field number which is that number which,
;;; when used as a second argument to wrapper-ref, will return that column
;;; of wrapper cache number.
;;;
;;; This code is written to allow flexibility as to how many wrapper cache
;;; numbers will be in each wrapper, and where they will be located.  It is
;;; also set up to allow port specific modifications to `pack' the wrapper
;;; cache numbers on machines where the addressing modes make that a good
;;; idea.
;;;
#-structure-wrapper
(progn
(eval-when (compile load eval)
(defconstant wrapper-layout
         '(number
           number
           number
           number
           number
           number
           number
           number
           state
           instance-slots-layout
           class-slots
           class
           no-of-instance-slots))
)

(eval-when (compile load eval)

(defun wrapper-field (type)
  (posq type wrapper-layout))

(defun next-wrapper-field (field-number)
  (position (nth field-number wrapper-layout)
        wrapper-layout
        :start (1+ field-number)))

(defmacro first-wrapper-cache-number-index ()
  `(wrapper-field 'number))

(defmacro next-wrapper-cache-number-index (field-number)
  `(next-wrapper-field ,field-number))

);eval-when

(defmacro wrapper-cache-number-vector (wrapper)
  wrapper)

(defmacro cache-number-vector-ref (cnv n)
  `(svref ,cnv ,n))


(defmacro wrapper-ref (wrapper n)
  `(svref ,wrapper ,n))

(defmacro wrapper-state (wrapper)
  `(wrapper-ref ,wrapper ,(wrapper-field 'state)))

(defmacro wrapper-instance-slots-layout (wrapper)
  `(wrapper-ref ,wrapper ,(wrapper-field 'instance-slots-layout)))

(defmacro wrapper-class-slots (wrapper)
  `(wrapper-ref ,wrapper ,(wrapper-field 'class-slots)))

(defmacro wrapper-class (wrapper)
  `(wrapper-ref ,wrapper ,(wrapper-field 'class)))

(defmacro wrapper-no-of-instance-slots (wrapper)
  `(wrapper-ref ,wrapper ,(wrapper-field 'no-of-instance-slots)))

(defmacro make-wrapper-internal ()
  `(let ((wrapper (make-array ,(length wrapper-layout) :adjustable nil)))
     ,@(gathering1 (collecting)
     (iterate ((i (interval :from 0))
           (desc (list-elements wrapper-layout)))
       (ecase desc
         (number
          (gather1 `(setf (wrapper-ref wrapper ,i)
                  (get-wrapper-cache-number))))
         ((state instance-slots-layout class-slots class no-of-instance-slots)))))
     (setf (wrapper-state wrapper) 't)
     wrapper))

(defun make-wrapper (no-of-instance-slots &optional class)
  (let ((wrapper (make-wrapper-internal)))
    (setf (wrapper-no-of-instance-slots wrapper) no-of-instance-slots)
    (setf (wrapper-class wrapper) class)
    wrapper))

)

; In CMUCL we want to do type checking as early as possible; structures help this.
#+structure-wrapper
(eval-when (compile load eval)

(defconstant wrapper-cache-number-vector-length 8)

(deftype cache-number-vector ()
  `(simple-array fixnum (8)))

(defconstant wrapper-layout (make-list wrapper-cache-number-vector-length
                       :initial-element 'number))

)

#+structure-wrapper
(progn

#-new-kcl-wrapper
(defun make-wrapper-cache-number-vector ()
  (let ((cnv (make-array #.wrapper-cache-number-vector-length
             :element-type 'fixnum)))
    (dotimes (i #.wrapper-cache-number-vector-length)
      (setf (aref cnv i) (get-wrapper-cache-number)))
    cnv))

(defstruct (wrapper
         #+new-kcl-wrapper (:include si::basic-wrapper)
         (:print-function print-wrapper)
         #-new-kcl-wrapper
         (:constructor make-wrapper (no-of-instance-slots &optional class))
         #+new-kcl-wrapper
         (:constructor make-wrapper-internal))
  #-new-kcl-wrapper
  (cache-number-vector (make-wrapper-cache-number-vector)
               :type cache-number-vector)
  #-new-kcl-wrapper
  (state t :type (or (member t) cons))
  ;;  either t or a list (state-sym new-wrapper)
  ;;           where state-sym is either :flush or :obsolete
  (instance-slots-layout nil :type list)
  (class-slots nil :type list)
  #-new-kcl-wrapper
  (no-of-instance-slots 0 :type fixnum)
  #-new-kcl-wrapper
  (class *the-class-t* :type class))

(unless (boundp '*the-class-t*) (setq *the-class-t* nil))

#+new-kcl-wrapper
(defmacro wrapper-no-of-instance-slots (wrapper)
  `(si::s-data-length ,wrapper))

#+new-kcl-wrapper
(defun make-wrapper (size &optional class)
  (multiple-value-bind (raw slot-positions)
      (if (< size 50)
      (values si::*all-t-s-type* si::*standard-slot-positions*)
      (values (make-array size :element-type 'unsigned-char)
          (let ((array (make-array size :element-type 'unsigned-short)))
            (dotimes (i size)
              (declare (fixnum i))
              (setf (aref array i) (* #.(si::size-of t) i))))))
    (make-wrapper-internal :length size
               :raw raw
               :print-function 'print-std-instance
               :slot-position slot-positions
               :size (* size #.(si::size-of t))
               :class class)))

(defun print-wrapper (wrapper stream depth)
  (declare (ignore depth))
  (printing-random-thing (wrapper stream)
    (format stream "Wrapper ~S" (wrapper-class wrapper))))

(defmacro first-wrapper-cache-number-index ()
  0)

(defmacro next-wrapper-cache-number-index (field-number)
  `(and (< ,field-number #.(1- wrapper-cache-number-vector-length))
        (1+ ,field-number)))

(defmacro cache-number-vector-ref (cnv n)
  `(#-kcl svref #+kcl aref ,cnv ,n))

)

(defmacro wrapper-cache-number-vector-ref (wrapper n)
  `(the fixnum
        (#-structure-wrapper svref #+structure-wrapper aref
          (wrapper-cache-number-vector ,wrapper) ,n)))

(defmacro class-no-of-instance-slots (class)
  `(wrapper-no-of-instance-slots (class-wrapper ,class)))

(defmacro wrapper-class* (wrapper)
  #-new-kcl-wrapper
  `(wrapper-class ,wrapper)
  #+new-kcl-wrapper
  `(let ((wrapper ,wrapper))
     (or (wrapper-class wrapper)
         (find-structure-class (si::s-data-name wrapper)))))

;;;
;;; The wrapper cache machinery provides general mechanism for trapping on
;;; the next access to any instance of a given class.  This mechanism is
;;; used to implement the updating of instances when the class is redefined
;;; (make-instances-obsolete).  The same mechanism is also used to update
;;; generic function caches when there is a change to the supers of a class.
;;;
;;; Basically, a given wrapper can be valid or invalid.  If it is invalid,
;;; it means that any attempt to do a wrapper cache lookup using the wrapper
;;; should trap.  Also, methods on slot-value-using-class check the wrapper
;;; validity as well.  This is done by calling check-wrapper-validity.
;;;

(defmacro invalid-wrapper-p (wrapper)
  `(neq (wrapper-state ,wrapper) 't))

(defvar *previous-nwrappers* (make-hash-table))

(defun invalidate-wrapper (owrapper state nwrapper)
  (ecase state
    ((:flush :obsolete)
     (let ((new-previous ()))
       ;;
       ;; First off, a previous call to invalidate-wrapper may have recorded
       ;; owrapper as an nwrapper to update to.  Since owrapper is about to
       ;; be invalid, it no longer makes sense to update to it.
       ;;
       ;; We go back and change the previously invalidated wrappers so that
       ;; they will now update directly to nwrapper.  This corresponds to a
       ;; kind of transitivity of wrapper updates.
       ;;
       (dolist (previous (gethash owrapper *previous-nwrappers*))
     (when (eq state ':obsolete)
       (setf (car previous) ':obsolete))
     (setf (cadr previous) nwrapper)
     (push previous new-previous))

       (let ((ocnv (wrapper-cache-number-vector owrapper)))
     (iterate ((type (list-elements wrapper-layout))
           (i (interval :from 0)))
           (when (eq type 'number) (setf (cache-number-vector-ref ocnv i) 0))))
       (push (setf (wrapper-state owrapper) (list state nwrapper))
         new-previous)

       (setf (gethash owrapper *previous-nwrappers*) ()
         (gethash nwrapper *previous-nwrappers*) new-previous)))))

(defun check-wrapper-validity (instance)
  (let* ((owrapper (wrapper-of instance))
     (state (wrapper-state owrapper)))
    (if (eq state  't)
    owrapper
    (let ((nwrapper
        (ecase (car state)
          (:flush
            (flush-cache-trap owrapper (cadr state) instance))
          (:obsolete
            (obsolete-instance-trap owrapper (cadr state) instance)))))
      ;;
      ;; This little bit of error checking is superfluous.  It only
      ;; checks to see whether the person who implemented the trap
      ;; handling screwed up.  Since that person is hacking internal
      ;; PCL code, and is not a user, this should be needless.  Also,
      ;; since this directly slows down instance update and generic
      ;; function cache refilling, feel free to take it out sometime
      ;; soon.
      ;;
      (cond ((neq nwrapper (wrapper-of instance))
         (error "Wrapper returned from trap not wrapper of instance."))
        ((invalid-wrapper-p nwrapper)
         (error "Wrapper returned from trap invalid.")))
      nwrapper))))

(defmacro check-wrapper-validity1 (object)
  (let ((owrapper (gensym)))
    `(let ((,owrapper (cond ((std-instance-p ,object)
                 (std-instance-wrapper ,object))
                ((fsc-instance-p ,object)
                 (fsc-instance-wrapper ,object))
                #+new-kcl-wrapper
                (t (built-in-wrapper-of ,object))
                #-new-kcl-wrapper
                (t (wrapper-of ,object)))))
       (if (eq 't (wrapper-state ,owrapper))
       ,owrapper
       (check-wrapper-validity ,object)))))


(defvar *free-caches* nil)

(defun get-cache (nkeys valuep limit-fn nlines)
  (let ((cache (or (without-interrupts (pop *free-caches*)) (make-cache))))
    (declare (type cache cache))
    (multiple-value-bind (cache-mask actual-size line-size nlines)
    (compute-cache-parameters nkeys valuep nlines)
      (setf (cache-nkeys cache) nkeys
        (cache-valuep cache) valuep
        (cache-nlines cache) nlines
        (cache-field cache) (first-wrapper-cache-number-index)
        (cache-limit-fn cache) limit-fn
        (cache-mask cache) cache-mask
        (cache-size cache) actual-size
        (cache-line-size cache) line-size
        (cache-max-location cache) (let ((line (1- nlines)))
                     (if (= nkeys 1)
                         (* line line-size)
                         (1+ (* line line-size))))
        (cache-vector cache) (get-cache-vector actual-size)
        (cache-overflow cache) nil)
      cache)))

(defun get-cache-from-cache (old-cache new-nlines
                 &optional (new-field (first-wrapper-cache-number-index)))
  (let ((nkeys (cache-nkeys old-cache))
    (valuep (cache-valuep old-cache))
    (cache (or (without-interrupts (pop *free-caches*)) (make-cache))))
    (declare (type cache cache))
    (multiple-value-bind (cache-mask actual-size line-size nlines)
    (if (= new-nlines (cache-nlines old-cache))
        (values (cache-mask old-cache) (cache-size old-cache)
            (cache-line-size old-cache) (cache-nlines old-cache))
        (compute-cache-parameters nkeys valuep new-nlines))
      (setf (cache-owner cache) (cache-owner old-cache)
        (cache-nkeys cache) nkeys
        (cache-valuep cache) valuep
        (cache-nlines cache) nlines
        (cache-field cache) new-field
        (cache-limit-fn cache) (cache-limit-fn old-cache)
        (cache-mask cache) cache-mask
        (cache-size cache) actual-size
        (cache-line-size cache) line-size
        (cache-max-location cache) (let ((line (1- nlines)))
                     (if (= nkeys 1)
                         (* line line-size)
                         (1+ (* line line-size))))
        (cache-vector cache) (get-cache-vector actual-size)
        (cache-overflow cache) nil)
      cache)))

(defun copy-cache (old-cache)
  (let* ((new-cache (copy-cache-internal old-cache))
     (size (cache-size old-cache))
     (old-vector (cache-vector old-cache))
     (new-vector (get-cache-vector size)))
    (declare (simple-vector old-vector new-vector))
    (dotimes (i size)
      (setf (svref new-vector i) (svref old-vector i)))
    (setf (cache-vector new-cache) new-vector)
    new-cache))

(defun free-cache (cache)
  (free-cache-vector (cache-vector cache))
  (setf (cache-vector cache) #())
  (setf (cache-owner cache) nil)
  (push cache *free-caches*)
  nil)

(defun compute-line-size (x)
  (power-of-two-ceiling x))

(defun compute-cache-parameters (nkeys valuep nlines-or-cache-vector)
  ;;(declare (values cache-mask actual-size line-size nlines))
  (declare (fixnum nkeys))
  (if (= nkeys 1)
      (let* ((line-size (if valuep 2 1))
         (cache-size (if (typep nlines-or-cache-vector 'fixnum)
                 (the fixnum
                  (* line-size
                     (the fixnum
                      (power-of-two-ceiling
                        nlines-or-cache-vector))))
                 (cache-vector-size nlines-or-cache-vector))))
    (declare (fixnum line-size cache-size))
    (values (logxor (the fixnum (1- cache-size)) (the fixnum (1- line-size)))
        cache-size
        line-size
        (the fixnum (floor cache-size line-size))))
      (let* ((line-size (power-of-two-ceiling (if valuep (1+ nkeys) nkeys)))
         (cache-size (if (typep nlines-or-cache-vector 'fixnum)
                 (the fixnum
                  (* line-size
                     (the fixnum
                      (power-of-two-ceiling
                        nlines-or-cache-vector))))
                 (1- (cache-vector-size nlines-or-cache-vector)))))
    (declare (fixnum line-size cache-size))
    (values (logxor (the fixnum (1- cache-size)) (the fixnum (1- line-size)))
        (the fixnum (1+ cache-size))
        line-size
        (the fixnum (floor cache-size line-size))))))



;;;
;;; The various implementations of computing a primary cache location from
;;; wrappers.  Because some implementations of this must run fast there are
;;; several implementations of the same algorithm.
;;;
;;; The algorithm is:
;;;
;;;  SUM       over the wrapper cache numbers,
;;;  ENSURING  that the result is a fixnum
;;;  MASK      the result against the mask argument.
;;;
;;;

;;;
;;; COMPUTE-PRIMARY-CACHE-LOCATION
;;;
;;; The basic functional version.  This is used by the cache miss code to
;;; compute the primary location of an entry.
;;;
(defun compute-primary-cache-location (field mask wrappers)
  (declare (type field-type field) (fixnum mask))
  (if (not (listp wrappers))
      (logand mask (the fixnum (wrapper-cache-number-vector-ref wrappers field)))
      (let ((location 0) (i 0))
    (declare (fixnum location i))
    (dolist (wrapper wrappers)
      ;;
      ;; First add the cache number of this wrapper to location.
      ;;
      (let ((wrapper-cache-number (wrapper-cache-number-vector-ref wrapper field)))
        (declare (fixnum wrapper-cache-number))
        (if (zerop wrapper-cache-number)
        (return-from compute-primary-cache-location 0)
        (setq location (the fixnum (+ location wrapper-cache-number)))))
      ;;
      ;; Then, if we are working with lots of wrappers, deal with
      ;; the wrapper-cache-number-mask stuff.
      ;;
      (when (and (not (zerop i))
             (zerop (mod i wrapper-cache-number-adds-ok)))
        (setq location
          (logand location wrapper-cache-number-mask)))
      (incf i))
    (the fixnum (1+ (logand mask location))))))

;;;
;;; COMPUTE-PRIMARY-CACHE-LOCATION-FROM-LOCATION
;;;
;;; This version is called on a cache line.  It fetches the wrappers from
;;; the cache line and determines the primary location.  Various parts of
;;; the cache filling code call this to determine whether it is appropriate
;;; to displace a given cache entry.
;;;
;;; If this comes across a wrapper whose cache-no is 0, it returns the symbol
;;; invalid to suggest to its caller that it would be provident to blow away
;;; the cache line in question.
;;;
(defun compute-primary-cache-location-from-location (to-cache from-location
                             &optional (from-cache to-cache))
  (declare (type cache to-cache from-cache) (fixnum from-location))
  (let ((result 0)
    (cache-vector (cache-vector from-cache))
    (field (cache-field to-cache))
    (mask (cache-mask to-cache))
    (nkeys (cache-nkeys to-cache)))
    (declare (type field-type field) (fixnum result mask nkeys)
         (simple-vector cache-vector))
    (dotimes (i nkeys)
      (let* ((wrapper (cache-vector-ref cache-vector (+ i from-location)))
         (wcn (wrapper-cache-number-vector-ref wrapper field)))
    (declare (fixnum wcn))
    (setq result (+ result wcn)))
      (when (and (not (zerop i))
         (zerop (mod i wrapper-cache-number-adds-ok)))
    (setq result (logand result wrapper-cache-number-mask))))
    (if (= nkeys 1)
    (logand mask result)
    (the fixnum (1+ (logand mask result))))))


;;;
;;;  NIL              means nothing so far, no actual arg info has NILs
;;;                   in the metatype
;;;  CLASS            seen all sorts of metaclasses
;;;                   (specifically, more than one of the next 4 values)
;;;  T                means everything so far is the class T
;;;  STANDARD-CLASS   seen only standard classes
;;;  BUILT-IN-CLASS   seen only built in classes
;;;  STRUCTURE-CLASS  seen only structure classes
;;;
(defun raise-metatype (metatype new-specializer)
  (let ((slot      (find-class 'slot-class))
    (standard  (find-class 'standard-class))
    (fsc       (find-class 'funcallable-standard-class))
    (structure (find-class 'structure-class))
    (built-in  (find-class 'built-in-class)))
    (flet ((specializer->metatype (x)
         (let ((meta-specializer
             (if (eq *boot-state* 'complete)
             (class-of (specializer-class x))
             (class-of x))))
           (cond ((eq x *the-class-t*) t)
             ((*subtypep meta-specializer standard)  'standard-instance)
             ((*subtypep meta-specializer fsc)       'standard-instance)
             ((*subtypep meta-specializer structure) 'structure-instance)
             ((*subtypep meta-specializer built-in)  'built-in-instance)
             ((*subtypep meta-specializer slot)      'slot-instance)
             (t (error "PCL can not handle the specializer ~S (meta-specializer ~S)."
                   new-specializer meta-specializer))))))
      ;;
      ;; We implement the following table.  The notation is
      ;; that X and Y are distinct meta specializer names.
      ;;
      ;;   NIL    <anything>    ===>  <anything>
      ;;    X      X            ===>      X
      ;;    X      Y            ===>    CLASS
      ;;
      (let ((new-metatype (specializer->metatype new-specializer)))
    (cond ((eq new-metatype 'slot-instance) 'class)
          ((null metatype) new-metatype)
          ((eq metatype new-metatype) new-metatype)
          (t 'class))))))

(defmacro with-dfun-wrappers ((args metatypes)
                  (dfun-wrappers invalid-wrapper-p
                         &optional wrappers classes types)
                  invalid-arguments-form
                  &body body)
  `(let* ((args-tail ,args) (,invalid-wrapper-p nil) (invalid-arguments-p nil)
      (,dfun-wrappers nil) (dfun-wrappers-tail nil)
      ,@(when wrappers
          `((wrappers-rev nil) (types-rev nil) (classes-rev nil))))
     (dolist (mt ,metatypes)
       (unless args-tail
     (setq invalid-arguments-p t)
     (return nil))
       (let* ((arg (pop args-tail))
          (wrapper nil)
          ,@(when wrappers
          `((class *the-class-t*)
            (type 't))))
     (unless (eq mt 't)
       (setq wrapper (wrapper-of arg))
       (when (invalid-wrapper-p wrapper)
         (setq ,invalid-wrapper-p t)
         (setq wrapper (check-wrapper-validity arg)))
       (cond ((null ,dfun-wrappers)
          (setq ,dfun-wrappers wrapper))
         ((not (consp ,dfun-wrappers))
          (setq dfun-wrappers-tail (list wrapper))
          (setq ,dfun-wrappers (cons ,dfun-wrappers dfun-wrappers-tail)))
         (t
          (let ((new-dfun-wrappers-tail (list wrapper)))
            (setf (cdr dfun-wrappers-tail) new-dfun-wrappers-tail)
            (setf dfun-wrappers-tail new-dfun-wrappers-tail))))
       ,@(when wrappers
           `((setq class (wrapper-class* wrapper))
         (setq type `(class-eq ,class)))))
     ,@(when wrappers
         `((push wrapper wrappers-rev)
           (push class classes-rev)
           (push type types-rev)))))
     (if invalid-arguments-p
     ,invalid-arguments-form
     (let* (,@(when wrappers
            `((,wrappers (nreverse wrappers-rev))
              (,classes (nreverse classes-rev))
              (,types (mapcar #'(lambda (class)
                      `(class-eq ,class))
                          ,classes)))))
       ,@body))))


;;;
;;; Some support stuff for getting a hold of symbols that we need when
;;; building the discriminator codes.  Its ok for these to be interned
;;; symbols because we don't capture any user code in the scope in which
;;; these symbols are bound.
;;;

(defvar *dfun-arg-symbols* '(.ARG0. .ARG1. .ARG2. .ARG3.))

(defun dfun-arg-symbol (arg-number)
  (or (nth arg-number (the list *dfun-arg-symbols*))
      (intern (format nil ".ARG~A." arg-number) *the-pcl-package*)))

(defvar *slot-vector-symbols* '(.SLOTS0. .SLOTS1. .SLOTS2. .SLOTS3.))

(defun slot-vector-symbol (arg-number)
  (or (nth arg-number (the list *slot-vector-symbols*))
      (intern (format nil ".SLOTS~A." arg-number) *the-pcl-package*)))

(defun make-dfun-lambda-list (metatypes applyp)
  (gathering1 (collecting)
    (iterate ((i (interval :from 0))
          (s (list-elements metatypes)))
      (progn s)
      (gather1 (dfun-arg-symbol i)))
    (when applyp
      (gather1 '&rest)
      (gather1 '.dfun-rest-arg.))))

(defun make-dlap-lambda-list (metatypes applyp)
  (gathering1 (collecting)
    (iterate ((i (interval :from 0))
          (s (list-elements metatypes)))
      (progn s)
      (gather1 (dfun-arg-symbol i)))
    (when applyp
      (gather1 '&rest))))

(defun make-emf-call (metatypes applyp fn-variable &optional emf-type)
  (let ((required
     (gathering1 (collecting)
        (iterate ((i (interval :from 0))
              (s (list-elements metatypes)))
          (progn s)
          (gather1 (dfun-arg-symbol i))))))
    `(,(if (eq emf-type 'fast-method-call)
       'invoke-effective-method-function-fast
       'invoke-effective-method-function)
      ,fn-variable ,applyp ,@required ,@(when applyp `(.dfun-rest-arg.)))))

(defun make-dfun-call (metatypes applyp fn-variable)
  (let ((required
      (gathering1 (collecting)
        (iterate ((i (interval :from 0))
              (s (list-elements metatypes)))
          (progn s)
          (gather1 (dfun-arg-symbol i))))))
    (if applyp
    `(function-apply   ,fn-variable ,@required .dfun-rest-arg.)
    `(function-funcall ,fn-variable ,@required))))

(defun make-dfun-arg-list (metatypes applyp)
  (let ((required
      (gathering1 (collecting)
        (iterate ((i (interval :from 0))
              (s (list-elements metatypes)))
          (progn s)
          (gather1 (dfun-arg-symbol i))))))
    (if applyp
    `(list* ,@required .dfun-rest-arg.)
    `(list ,@required))))

(defun make-fast-method-call-lambda-list (metatypes applyp)
  (gathering1 (collecting)
    (gather1 '.pv-cell.)
    (gather1 '.next-method-call.)
    (iterate ((i (interval :from 0))
          (s (list-elements metatypes)))
      (progn s)
      (gather1 (dfun-arg-symbol i)))
    (when applyp
      (gather1 '.dfun-rest-arg.))))


;;;
;;; Its too bad Common Lisp compilers freak out when you have a defun with
;;; a lot of LABELS in it.  If I could do that I could make this code much
;;; easier to read and work with.
;;;
;;; Ahh Scheme...
;;;
;;; In the absence of that, the following little macro makes the code that
;;; follows a little bit more reasonable.  I would like to add that having
;;; to practically write my own compiler in order to get just this simple
;;; thing is something of a drag.
;;;
(eval-when (compile load eval)

(defvar *cache* nil)

(defconstant *local-cache-functions*
  '((cache () .cache.)
    (nkeys () (cache-nkeys .cache.))
    (line-size () (cache-line-size .cache.))
    (vector () (cache-vector .cache.))
    (valuep () (cache-valuep .cache.))
    (nlines () (cache-nlines .cache.))
    (max-location () (cache-max-location .cache.))
    (limit-fn () (cache-limit-fn .cache.))
    (size () (cache-size .cache.))
    (mask () (cache-mask .cache.))
    (field () (cache-field .cache.))
    (overflow () (cache-overflow .cache.))

    ;;
    ;; Return T IFF this cache location is reserved.  The only time
    ;; this is true is for line number 0 of an nkeys=1 cache.
    ;;
    (line-reserved-p (line)
      (declare (fixnum line))
      (and (= (nkeys) 1)
           (= line 0)))
    ;;
    (location-reserved-p (location)
      (declare (fixnum location))
      (and (= (nkeys) 1)
           (= location 0)))
    ;;
    ;; Given a line number, return the cache location.  This is the
    ;; value that is the second argument to cache-vector-ref.  Basically,
    ;; this deals with the offset of nkeys>1 caches and multiplies
    ;; by line size.
    ;;
    (line-location (line)
      (declare (fixnum line))
      (when (line-reserved-p line)
        (error "line is reserved"))
      (if (= (nkeys) 1)
      (the fixnum (* line (line-size)))
      (the fixnum (1+ (the fixnum (* line (line-size)))))))
    ;;
    ;; Given a cache location, return the line.  This is the inverse
    ;; of LINE-LOCATION.
    ;;
    (location-line (location)
      (declare (fixnum location))
      (if (= (nkeys) 1)
      (floor location (line-size))
      (floor (the fixnum (1- location)) (line-size))))
    ;;
    ;; Given a line number, return the wrappers stored at that line.
    ;; As usual, if nkeys=1, this returns a single value.  Only when
    ;; nkeys>1 does it return a list.  An error is signalled if the
    ;; line is reserved.
    ;;
    (line-wrappers (line)
      (declare (fixnum line))
      (when (line-reserved-p line) (error "Line is reserved."))
      (location-wrappers (line-location line)))
    ;;
    (location-wrappers (location) ; avoid multiplies caused by line-location
      (declare (fixnum location))
      (if (= (nkeys) 1)
      (cache-vector-ref (vector) location)
      (let ((list (make-list (nkeys)))
        (vector (vector)))
        (declare (simple-vector vector))
        (dotimes (i (nkeys) list)
          (setf (nth i list) (cache-vector-ref vector (+ location i)))))))
    ;;
    ;; Given a line number, return true IFF the line's
    ;; wrappers are the same as wrappers.
    ;;
    (line-matches-wrappers-p (line wrappers)
      (declare (fixnum line))
      (and (not (line-reserved-p line))
           (location-matches-wrappers-p (line-location line) wrappers)))
    ;;
    (location-matches-wrappers-p (loc wrappers) ; must not be reserved
      (declare (fixnum loc))
      (let ((cache-vector (vector)))
    (declare (simple-vector cache-vector))
    (if (= (nkeys) 1)
        (eq wrappers (cache-vector-ref cache-vector loc))
        (dotimes (i (nkeys) t)
          (unless (eq (pop wrappers) (cache-vector-ref cache-vector (+ loc i)))
        (return nil))))))
    ;;
    ;; Given a line number, return the value stored at that line.
    ;; If valuep is NIL, this returns NIL.  As with line-wrappers,
    ;; an error is signalled if the line is reserved.
    ;;
    (line-value (line)
      (declare (fixnum line))
      (when (line-reserved-p line) (error "Line is reserved."))
      (location-value (line-location line)))
    ;;
    (location-value (loc)
      (declare (fixnum loc))
      (and (valuep)
           (cache-vector-ref (vector) (+ loc (nkeys)))))
    ;;
    ;; Given a line number, return true IFF that line has data in
    ;; it.  The state of the wrappers stored in the line is not
    ;; checked.  An error is signalled if line is reserved.
    (line-full-p (line)
      (when (line-reserved-p line) (error "Line is reserved."))
      (not (null (cache-vector-ref (vector) (line-location line)))))
    ;;
    ;; Given a line number, return true IFF the line is full and
    ;; there are no invalid wrappers in the line, and the line's
    ;; wrappers are different from wrappers.
    ;; An error is signalled if the line is reserved.
    ;;
    (line-valid-p (line wrappers)
      (declare (fixnum line))
      (when (line-reserved-p line) (error "Line is reserved."))
      (location-valid-p (line-location line) wrappers))
    ;;
    (location-valid-p (loc wrappers)
      (declare (fixnum loc))
      (let ((cache-vector (vector))
        (wrappers-mismatch-p (null wrappers)))
    (declare (simple-vector cache-vector))
    (dotimes (i (nkeys) wrappers-mismatch-p)
      (let ((wrapper (cache-vector-ref cache-vector (+ loc i))))
        (when (or (null wrapper)
              (invalid-wrapper-p wrapper))
          (return nil))
        (unless (and wrappers
             (eq wrapper
                 (if (consp wrappers) (pop wrappers) wrappers)))
          (setq wrappers-mismatch-p t))))))
    ;;
    ;; How many unreserved lines separate line-1 and line-2.
    ;;
    (line-separation (line-1 line-2)
     (declare (fixnum line-1 line-2))
     (let ((diff (the fixnum (- line-2 line-1))))
       (declare (fixnum diff))
       (when (minusp diff)
     (setq diff (+ diff (nlines)))
     (when (line-reserved-p 0)
       (setq diff (1- diff))))
       diff))
    ;;
    ;; Given a cache line, get the next cache line.  This will not
    ;; return a reserved line.
    ;;
    (next-line (line)
     (declare (fixnum line))
     (if (= line (the fixnum (1- (nlines))))
     (if (line-reserved-p 0) 1 0)
     (the fixnum (1+ line))))
    ;;
    (next-location (loc)
      (declare (fixnum loc))
      (if (= loc (max-location))
      (if (= (nkeys) 1)
          (line-size)
          1)
      (the fixnum (+ loc (line-size)))))
    ;;
    ;; Given a line which has a valid entry in it, this will return
    ;; the primary cache line of the wrappers in that line.  We just
    ;; call COMPUTE-PRIMARY-CACHE-LOCATION-FROM-LOCATION, this is an
    ;; easier packaging up of the call to it.
    ;;
    (line-primary (line)
      (declare (fixnum line))
      (location-line (line-primary-location line)))
    ;;
    (line-primary-location (line)
     (declare (fixnum line))
     (compute-primary-cache-location-from-location
       (cache) (line-location line)))
    ))

(defmacro with-local-cache-functions ((cache) &body body)
  `(let ((.cache. ,cache))
     (declare (type cache .cache.))
     (macrolet ,(mapcar #'(lambda (fn)
                `(,(car fn) ,(cadr fn)
                    `(let (,,@(mapcar #'(lambda (var)
                              ``(,',var ,,var))
                              (cadr fn)))
                    ,@',(cddr fn))))
            *local-cache-functions*)
       ,@body)))

)

;;;
;;; Here is where we actually fill, recache and expand caches.
;;;
;;; The functions FILL-CACHE and PROBE-CACHE are the ONLY external
;;; entrypoints into this code.
;;;
;;; FILL-CACHE returns 1 value: a new cache
;;;
;;;   a wrapper field number
;;;   a cache
;;;   a mask
;;;   an absolute cache size (the size of the actual vector)
;;; It tries to re-adjust the cache every time it makes a new fill.  The
;;; intuition here is that we want uniformity in the number of probes needed to
;;; find an entry.  Furthermore, adjusting has the nice property of throwing out
;;; any entries that are invalid.
;;;
(defvar *cache-expand-threshold* 1.25)

(defun fill-cache (cache wrappers value &optional free-cache-p)
  ;;(declare (values cache))
  (unless wrappers ; fill-cache won't return if wrappers is nil, might as well check.
    (error "fill-cache: wrappers arg is NIL!"))
  (or (fill-cache-p nil cache wrappers value)
      (and (< (ceiling (* (cache-count cache) 1.25))
          (if (= (cache-nkeys cache) 1)
          (1- (cache-nlines cache))
          (cache-nlines cache)))
       (adjust-cache cache wrappers value free-cache-p))
      (expand-cache cache wrappers value free-cache-p)))

(defvar *check-cache-p* nil)

(defmacro maybe-check-cache (cache)
  `(progn
     (when *check-cache-p*
       (check-cache ,cache))
     ,cache))

(defun check-cache (cache)
  (with-local-cache-functions (cache)
    (let ((location (if (= (nkeys) 1) 0 1))
      (limit (funcall (limit-fn) (nlines))))
      (dotimes (i (nlines) cache)
    (when (and (not (location-reserved-p location))
           (line-full-p i))
      (let* ((home-loc (compute-primary-cache-location-from-location
                cache location))
         (home (location-line (if (location-reserved-p home-loc)
                      (next-location home-loc)
                      home-loc)))
         (sep (when home (line-separation home i))))
        (when (and sep (> sep limit))
          (error "bad cache ~S ~@
                      value at location ~D is ~D lines from its home. limit is ~D."
             cache location sep limit))))
    (setq location (next-location location))))))

(defun probe-cache (cache wrappers &optional default limit-fn)
  ;;(declare (values value))
  (unless wrappers (error "probe-cache: wrappers arg is NIL!"))
  (with-local-cache-functions (cache)
    (let* ((location (compute-primary-cache-location (field) (mask) wrappers))
       (limit (funcall (or limit-fn (limit-fn)) (nlines))))
      (declare (fixnum location limit))
      (when (location-reserved-p location)
    (setq location (next-location location)))
      (dotimes (i (1+ limit))
    (when (location-matches-wrappers-p location wrappers)
      (return-from probe-cache (or (not (valuep))
                       (location-value location))))
    (setq location (next-location location)))
      (dolist (entry (overflow))
    (when (equal (car entry) wrappers)
      (return-from probe-cache (or (not (valuep))
                       (cdr entry)))))
      default)))

(defun map-cache (function cache &optional set-p)
  (with-local-cache-functions (cache)
    (let ((set-p (and set-p (valuep))))
      (dotimes (i (nlines) cache)
    (unless (or (line-reserved-p i) (not (line-valid-p i nil)))
      (let ((value (funcall function (line-wrappers i) (line-value i))))
        (when set-p
          (setf (cache-vector-ref (vector) (+ (line-location i) (nkeys)))
            value)))))
      (dolist (entry (overflow))
    (let ((value (funcall function (car entry) (cdr entry))))
      (when set-p
        (setf (cdr entry) value))))))
  cache)

(defun cache-count (cache)
  (with-local-cache-functions (cache)
    (let ((count 0))
      (declare (fixnum count))
      (dotimes (i (nlines) count)
    (unless (line-reserved-p i)
      (when (line-full-p i)
        (incf count)))))))

(defun entry-in-cache-p (cache wrappers value)
  (declare (ignore value))
  (with-local-cache-functions (cache)
    (dotimes (i (nlines))
      (unless (line-reserved-p i)
    (when (equal (line-wrappers i) wrappers)
      (return t))))))

;;;
;;; returns T or NIL
;;;
(defun fill-cache-p (forcep cache wrappers value)
  (with-local-cache-functions (cache)
    (let* ((location (compute-primary-cache-location (field) (mask) wrappers))
       (primary (location-line location)))
      (declare (fixnum location primary))
      (multiple-value-bind (free emptyp)
      (find-free-cache-line primary cache wrappers)
    (when (or forcep emptyp)
      (when (not emptyp)
        (push (cons (line-wrappers free) (line-value free))
          (cache-overflow cache)))
      ;;(fill-line free wrappers value)
      (let ((line free))
        (declare (fixnum line))
        (when (line-reserved-p line)
          (error "Attempt to fill a reserved line."))
        (let ((loc (line-location line))
          (cache-vector (vector)))
          (declare (fixnum loc) (simple-vector cache-vector))
          (cond ((= (nkeys) 1)
             (setf (cache-vector-ref cache-vector loc) wrappers)
             (when (valuep)
               (setf (cache-vector-ref cache-vector (1+ loc)) value)))
            (t
             (let ((i 0))
               (declare (fixnum i))
               (dolist (w wrappers)
             (setf (cache-vector-ref cache-vector (+ loc i)) w)
             (setq i (the fixnum (1+ i)))))
             (when (valuep)
               (setf (cache-vector-ref cache-vector (+ loc (nkeys)))
                 value))))
          (maybe-check-cache cache))))))))

(defun fill-cache-from-cache-p (forcep cache from-cache from-line)
  (declare (fixnum from-line))
  (with-local-cache-functions (cache)
    (let ((primary (location-line (compute-primary-cache-location-from-location
                   cache (line-location from-line) from-cache))))
      (declare (fixnum primary))
      (multiple-value-bind (free emptyp)
      (find-free-cache-line primary cache)
    (when (or forcep emptyp)
      (when (not emptyp)
        (push (cons (line-wrappers free) (line-value free))
          (cache-overflow cache)))
      ;;(transfer-line from-cache-vector from-line cache-vector free)
      (let ((from-cache-vector (cache-vector from-cache))
        (to-cache-vector (vector))
        (to-line free))
        (declare (fixnum to-line))
        (if (line-reserved-p to-line)
        (error "transfering something into a reserved cache line.")
        (let ((from-loc (line-location from-line))
              (to-loc (line-location to-line)))
          (declare (fixnum from-loc to-loc))
          (modify-cache to-cache-vector
                (dotimes (i (line-size))
                  (setf (cache-vector-ref to-cache-vector
                              (+ to-loc i))
                    (cache-vector-ref from-cache-vector
                              (+ from-loc i)))))))
        (maybe-check-cache cache)))))))

;;;
;;; Returns NIL or (values <field> <cache-vector>)
;;;
;;; This is only called when it isn't possible to put the entry in the cache
;;; the easy way.  That is, this function assumes that FILL-CACHE-P has been
;;; called as returned NIL.
;;;
;;; If this returns NIL, it means that it wasn't possible to find a wrapper
;;; field for which all of the entries could be put in the cache (within the
;;; limit).
;;;
(defun adjust-cache (cache wrappers value free-old-cache-p)
  (with-local-cache-functions (cache)
    (let ((ncache (get-cache-from-cache cache (nlines) (field))))
      (do ((nfield (cache-field ncache) (next-wrapper-cache-number-index nfield)))
      ((null nfield) (free-cache ncache) nil)
    (setf (cache-field ncache) nfield)
    (labels ((try-one-fill-from-line (line)
           (fill-cache-from-cache-p nil ncache cache line))
         (try-one-fill (wrappers value)
           (fill-cache-p nil ncache wrappers value)))
      (if (and (dotimes (i (nlines) t)
             (when (and (null (line-reserved-p i))
                (line-valid-p i wrappers))
               (unless (try-one-fill-from-line i) (return nil))))
           (dolist (wrappers+value (cache-overflow cache) t)
             (unless (try-one-fill (car wrappers+value) (cdr wrappers+value))
               (return nil)))
           (try-one-fill wrappers value))
          (progn (when free-old-cache-p (free-cache cache))
             (return (maybe-check-cache ncache)))
          (flush-cache-vector-internal (cache-vector ncache))))))))


;;;
;;; returns: (values <cache>)
;;;
(defun expand-cache (cache wrappers value free-old-cache-p)
  ;;(declare (values cache))
  (with-local-cache-functions (cache)
    (let ((ncache (get-cache-from-cache cache (* (nlines) 2))))
      (labels ((do-one-fill-from-line (line)
         (unless (fill-cache-from-cache-p nil ncache cache line)
           (do-one-fill (line-wrappers line) (line-value line))))
           (do-one-fill (wrappers value)
         (setq ncache (or (adjust-cache ncache wrappers value t)
                  (fill-cache-p t ncache wrappers value))))
           (try-one-fill (wrappers value)
         (fill-cache-p nil ncache wrappers value)))
    (dotimes (i (nlines))
      (when (and (null (line-reserved-p i))
             (line-valid-p i wrappers))
        (do-one-fill-from-line i)))
    (dolist (wrappers+value (cache-overflow cache))
      (unless (try-one-fill (car wrappers+value) (cdr wrappers+value))
        (do-one-fill (car wrappers+value) (cdr wrappers+value))))
    (unless (try-one-fill wrappers value)
      (do-one-fill wrappers value))
    (when free-old-cache-p (free-cache cache))
    (maybe-check-cache ncache)))))


;;;
;;; This is the heart of the cache filling mechanism.  It implements the decisions
;;; about where entries are placed.
;;;
;;; Find a line in the cache at which a new entry can be inserted.
;;;
;;;   <line>
;;;   <empty?>           is <line> in fact empty?
;;;
(defun find-free-cache-line (primary cache &optional wrappers)
  ;;(declare (values line empty?))
  (declare (fixnum primary))
  (with-local-cache-functions (cache)
    (when (line-reserved-p primary) (setq primary (next-line primary)))
    (let ((limit (funcall (limit-fn) (nlines)))
      (wrappedp nil)
      (lines nil)
      (p primary) (s primary))
      (declare (fixnum p s limit))
      (block find-free
    (loop
     ;; Try to find a free line starting at <s>.  <p> is the
     ;; primary line of the entry we are finding a free
     ;; line for, it is used to compute the seperations.
     (do* ((line s (next-line line))
           (nsep (line-separation p s) (1+ nsep)))
          (())
       (declare (fixnum line nsep))
       (when (null (line-valid-p line wrappers)) ;If this line is empty or
         (push line lines)        ;invalid, just use it.
         (return-from find-free))
       (when (and wrappedp (>= line primary))
         ;; have gone all the way around the cache, time to quit
         (return-from find-free-cache-line (values primary nil)))
       (let ((osep (line-separation (line-primary line) line)))
         (when (>= osep limit)
           (return-from find-free-cache-line (values primary nil)))
         (when (cond ((= nsep limit) t)
             ((= nsep osep) (zerop (random 2)))
             ((> nsep osep) t)
             (t nil))
           ;; See if we can displace what is in this line so that we
           ;; can use the line.
           (when (= line (the fixnum (1- (nlines)))) (setq wrappedp t))
           (setq p (line-primary line))
           (setq s (next-line line))
           (push line lines)
           (return nil)))
       (when (= line (the fixnum (1- (nlines)))) (setq wrappedp t)))))
      ;; Do all the displacing.
      (loop
       (when (null (cdr lines)) (return nil))
       (let ((dline (pop lines))
         (line (car lines)))
     (declare (fixnum dline line))
     ;;Copy from line to dline (dline is known to be free).
     (let ((from-loc (line-location line))
           (to-loc (line-location dline))
           (cache-vector (vector)))
       (declare (fixnum from-loc to-loc) (simple-vector cache-vector))
       (modify-cache cache-vector
             (dotimes (i (line-size))
               (setf (cache-vector-ref cache-vector (+ to-loc i))
                 (cache-vector-ref cache-vector (+ from-loc i)))
               (setf (cache-vector-ref cache-vector (+ from-loc i))
                 nil))))))
      (values (car lines) t))))

(defun default-limit-fn (nlines)
  (case nlines
    ((1 2 4) 1)
    ((8 16)  4)
    (otherwise 6)))

(defvar *empty-cache* (make-cache)) ; for defstruct slot initial value forms

;;;
;;; pre-allocate generic function caches.  The hope is that this will put
;;; them nicely together in memory, and that that may be a win.  Of course
;;; the first gc copy will probably blow that out, this really wants to be
;;; wrapped in something that declares the area static.
;;;
;;; This preallocation only creates about 25% more caches than PCL itself
;;; uses.  Some ports may want to preallocate some more of these.
;;;
(eval-when (load)
  (dolist (n-size '((1 513)(3 257)(3 129)(14 128)(6 65)(2 64)(7 33)(16 32)
            (16 17)(32 16)(64 9)(64 8)(6 5)(128 4)(35 2)))
    (let ((n (car n-size))
      (size (cadr n-size)))
      (mapcar #'free-cache-vector
          (mapcar #'get-cache-vector
              (make-list n :initial-element size))))))

(defun caches-to-allocate ()
  (sort (let ((l nil))
      (maphash #'(lambda (size entry)
               (push (list (car entry) size) l))
           pcl::*free-caches*)
      l)
    #'> :key #'cadr))