Mercurial > core / lisp/lib/obj/hash/castable.lisp

 ;;; lib/obj/hash/castable.lisp --- CAS Table
 
 ;; This implementation was written by Shinmera:
 ;; https://github.com/Shinmera/luckless/blob/master/cat.lisp
 
 ;; It is based on the JVM implementation of some concurrent data
 ;; structures.
 
 ;;; Code:
 (in-package :obj/hash)
 
 (eval-always
   (defstruct (prime (:constructor prime (value)))
     (value nil :type t))
 
   (defmethod make-load-form ((self prime) &optional environment)
     (declare (ignore environment))
     `(prime 'prime)))
 
 (defconstant max-spin 2)
 (defconstant reprobe-limit 10)
 (defconstant min-size-log 3)
 (defconstant min-size (ash 1 min-size-log))
 (defconstant no-match-old 'no-match-old)
 (defconstant match-any 'match-any)
 (defconstant tombstone 'tombstone)
 (defconstant tombprime (if (boundp 'tombprime) tombprime (prime tombstone)))
 (defconstant no-value 'no-value)
 
 ;;; Cat
 (defstruct (cat
             (:constructor %make-cat (next table))
             (:conc-name %cat-))
   (resizers 0 :type fixnum)
   (next nil :type t)
   (sum-cache most-negative-fixnum :type fixnum)
   (fuzzy-sum-cache 0 :type fixnum)
   (fuzzy-time 0 :type fixnum)
   (table nil :type simple-vector))
 
 (defun make-cat (next size initial-element)
   (declare (type fixnum initial-element))
   (declare (type fixnum size))
   (let ((table (make-array size :initial-element 0)))
     (setf (aref table 0) initial-element)
     (%make-cat next table)))
 
 (declaim (ftype (function (cat fixnum) fixnum) cat-sum))
 ;; L199 long sum(long)
 (defun cat-sum (cat mask)
   (declare (type fixnum mask))
   (declare (optimize speed))
   (let ((sum (%cat-sum-cache cat)))
     (cond ((/= most-negative-fixnum sum)
            sum)
           (T
            (setf sum (if (null (%cat-next cat))
                          0
                          (cat-sum (%cat-next cat) mask)))
            (let ((%t (%cat-table cat)))
              (dotimes (i (length %t))
                (incf sum (logand (svref %t i) (lognot mask))))
              (setf (%cat-sum-cache cat) sum)
              sum)))))
 
 (declaim (ftype (function (cat fixnum) fixnum) cat-sum~))
 ;; L212 long estimate_sum(long)
 (defun cat-sum~ (cat mask)
   (declare (type fixnum mask))
   (declare (optimize speed))
   (cond ((<= (length (%cat-table cat)) 64)
          (cat-sum cat mask))
         (T
          (let ((millis (get-internal-real-time)))
            (when (/= millis (%cat-fuzzy-time cat))
              (setf (%cat-fuzzy-sum-cache cat) (cat-sum cat mask))
              (setf (%cat-fuzzy-time cat) millis))
            (%cat-fuzzy-sum-cache cat)))))
 
 ;;; Counter
 (defstruct (counter (:constructor make-counter ())
                     (:conc-name %counter-))
   ;; Why is this slot at L97, after all the methods? I almost missed it, reading
   ;; the source code.
   (cat (make-cat NIL 4 0) :type cat))
 
 (declaim (inline decf-counter))
 ;; L41 decrement(), but with a delta argument.
 (defun decf-counter (counter &optional (delta 1))
   (declare (type fixnum delta))
   (counter-add-if-mask counter (- delta) 0))
 
 (declaim (inline incf-counter))
 ;; L43 increment(), but with a delta increment.
 (defun incf-counter (counter &optional (delta 1))
   (declare (type fixnum delta))
   (counter-add-if-mask counter delta 0))
 
 ;; L48 set(long)
 (defun (setf counter-value) (x counter)
   (declare (optimize speed))
   (declare (type fixnum x))
   (loop with new = (make-cat NIL 4 x)
         until (sb-ext:cas (%counter-cat counter) (%counter-cat counter) new)))
 
 (declaim (inline counter-value))
 ;; L59 get()
 (defun counter-value (counter)
   (cat-sum (%counter-cat counter) 0))
 
 (declaim (inline counter-value~))
 ;; L69 estimate_get()
 (defun counter-value~ (counter)
   (cat-sum~ (%counter-cat counter) 0))
 
 ;; L150 add_if_mask(long, long, int, ConcurrentAutoTable)
 ;; This is a method in the CAT in the Java implementation, but here the
 ;; ConcurrentAutoTable (counter) is the object being acted upon.
 (defun counter-add-if-mask (counter x mask)
   (declare (type fixnum x mask))
   (declare (optimize speed))
   (let* ((cat (%counter-cat counter))
          (%t (%cat-table cat))
          (idx (logand *global-hash* (1- (length %t))))
          (old (the fixnum (svref %t idx)))
          ;; Try once quickly
          (ok (sb-ext:cas (svref %t idx) (logand old (lognot mask)) (+ old x))))
     (flet ((fail () (return-from counter-add-if-mask old)))
       ;; Clear the cache
       (when (/= (%cat-sum-cache cat) most-negative-fixnum)
         (setf (%cat-sum-cache cat) most-negative-fixnum))
       (when ok (fail))
       (when (/= 0 (logand old mask)) (fail))
       ;; Try some more
       (let ((cnt 0))
         (declare (type fixnum cnt))
         (loop (setf old (the fixnum (svref %t idx)))
               (when (/= 0 (logand old mask)) (fail))
               (when (sb-ext:cas (svref %t idx) old (+ old x)) (return))
               (incf cnt))
         ;; Make sure we don't spin too long
         (when (< cnt MAX-SPIN) (fail))
         ;; Or grow too big
         (when (<= (* 1024 1024) (length %t)) (fail))
         ;; We are contending too much, increase the size in hopes it'll help
         (let ((r (%cat-resizers cat))
               (newbytes (ash (ash (length %t) 1) 4)))
           (declare (type fixnum r newbytes))
           (loop while (not (sb-ext:cas (%cat-resizers cat) r (+ r newbytes)))
                 do (setf r (%cat-resizers cat)))
           (incf r newbytes)
           ;; Already doubled up, don't bother
           (unless (eql cat (%counter-cat counter))
             (fail))
           ;; Did we try to allocate too often already?
           (when (/= 0 (ash r -17))
             (sleep (/ (ash r -17) 1000))
             (unless (eql cat (%counter-cat counter))
               (fail)))
           ;; Try to extend the CAT once, if it fails another thread
           ;; already did it for us so we don't have to retry.
           (let ((new (make-cat cat (* (length %t) 2) 0)))
             (sb-ext:cas (%counter-cat counter) cat new)
             (fail)))))))
 
 ;;; CAS Table
 (declaim (ftype (function (unsigned-byte) fixnum) rehash)
          (inline rehash))
 
 (defun rehash (h)
   "Spread bits of the hash H around."
   (declare (optimize speed))
   (declare (type (integer 0) h))
   (let ((h (logand h most-positive-fixnum)))
     (declare (type (unsigned-byte 64) h))
     (incf h (logior (logand most-positive-fixnum (ash h 15)) #xffffcd7d))
     (setf h (logior h (ash h -10)))
     (incf h (logand most-positive-fixnum (ash h 3)))
     (setf h (logior h (ash h -6)))
     (incf h (logand most-positive-fixnum (+ (ash h 2) (ash h 14))))
     (setf h (logior h (ash h -16)))
     (logand h most-positive-fixnum)))
 
 (declaim (inline reprobe-limit))
 (defun reprobe-limit (len)
   (+ reprobe-limit (ash len -2)))
 
 ;; L713, private class CHM
 ;; "The control structure for the NonBlockingHashMap"
 (defstruct (chm
             (:constructor make-chm (size))
             (:conc-name %chm-))
   (size (error "no size?") :type counter)
   (slots (make-counter) :type counter)
   (newkvs NIL :type (or null simple-vector))
   (resizers 0 :type fixnum)
   (copy-idx 0 :type fixnum)
   (copy-done 0 :type fixnum))
 (declaim (ftype (function (chm) fixnum)
                 %chm-resizers %chm-copy-idx %chm-copy-done))
 
 ;; L716, int size()
 (declaim (inline chm-size))
 (defun chm-size (chm)
   (counter-value (%chm-size chm)))
 
 ;; L729, int slots()
 (declaim (inline chm-slots))
 (defun chm-slots (chm)
   (counter-value (%chm-slots chm)))
 
 (declaim (inline cas-newkvs))
 ;; L742, boolean CAS_newkvs(Object[])
 (defun cas-newkvs (chm newkvs)
   (loop while (null (%chm-newkvs chm))
         do (when (sb-ext:cas (%chm-newkvs chm) NIL newkvs)
              (return T))
         finally (return NIL)))
 
 ;; Heuristic to test if the table is too full and we should make a new one.
 (declaim (inline table-full-p))
 ;; L780, boolean tableFull(int, int)
 (defun table-full-p (chm reprobe-cnt len)
   (and (<= REPROBE-LIMIT reprobe-cnt)
        (<= (reprobe-limit len) (counter-value~ (%chm-slots chm)))))
 
 (defstruct (castable
             (:constructor %make-castable (kvs last-resize test hasher))
             (:conc-name %castable-))
   (kvs (error "no KVS?") :type simple-vector)
   (last-resize (error "no LAST-RESIZE?") :type fixnum)
   (reprobes (make-counter) :type counter)
   (test (error "no TEST?") :type (function (T T) boolean))
   (hasher (error "no HASHER?") :type (function (T) fixnum)))
 
 (declaim (inline chm))
 (declaim (ftype (function (simple-vector) chm) chm))
 ;; L138, static CHM chm(Object[])
 (defun chm (kvs)
   (svref kvs 0))
 
 (declaim (inline hashes))
 (declaim (ftype (function (simple-vector) (simple-array fixnum)) hashes))
 ;; L139, static int[] hashes(Object[]) 
 (defun hashes (kvs)
   (svref kvs 1))
 
 (declaim (inline len))
 (declaim (ftype (function (simple-vector) (unsigned-byte 32)) len))
 ;; L140, static int len(Object[])
 (defun len (kvs)
   (the (unsigned-byte 32) (ash (- (length kvs) 2) -1)))
 
 (declaim (inline key))
 (declaim (ftype (function (simple-vector (unsigned-byte 32)) T) key))
 ;; L175 static Object key(Object[], int)
 (defun key (kvs idx)
   (svref kvs (+ 2 (ash idx 1))))
 
 (declaim (inline val))
 (declaim (ftype (function (simple-vector (unsigned-byte 32)) T) val))
 ;; L176 static Object val(Object[], int)
 (defun val (kvs idx)
   (svref kvs (+ 3 (ash idx 1))))
 
 (declaim (inline cas-key))
 ;; L177 static boolean CAS_key(Object[], int, Object, Object)
 (defun cas-key (kvs idx old key)
   (declare (simple-vector kvs))
   (sb-ext:cas (svref kvs (+ 2 (ash idx 1))) old key))
 
 (declaim (inline cas-val))
 ;; L180 static boolean CAS_val(Object[], int, Object, Object)
 (defun cas-val (kvs idx old val)
   (declare (simple-vector kvs))
   (sb-ext:cas (svref kvs (+ 3 (ash idx 1))) old val))
 
 ;; L237 long reprobes()
 (defun reprobes (table)
   (prog1 (counter-value (%castable-reprobes table))
     (setf (%castable-reprobes table) (make-counter))))
 
 (defun determine-hasher (test)
   ;; TODO 2024-09-23: 
   (or (cond ;; ((eq test #'eq) #'sb-impl::eq-hash) ;; package-lock violation
             ((eq test #'eql) #'sb-impl::eql-hash)
             ((eq test #'equal) #'sb-impl::equal-hash)
             ((eq test #'equalp) #'sb-impl::equalp-hash)
              ;; FIXME: implement own equalp hash
             (t (third (find test sb-impl::*user-hash-table-tests* :key #'second))))
       (error "Don't know a hasher for ~a." test)))
 
 (defvar *maximum-size* (* 8 1024 1024))
 (defun make-castable (&key test size hash-function)
   (let* ((size (min *maximum-size* (max MIN-SIZE (or size 0))))
          (test (etypecase test
                  (null #'eql)
                  (function test)
                  (symbol (fdefinition test))))
          (hash-function (etypecase hash-function
                           (null (determine-hasher test))
                           (function hash-function)
                           (symbol (fdefinition hash-function)))))
     (let ((power-of-two (expt 2 (integer-length size))))
       (let ((kvs (make-array (+ 2 (ash power-of-two 1)) :initial-element NO-VALUE)))
         (setf (svref kvs 0) (make-chm (make-counter)))
         (setf (svref kvs 1) (make-array power-of-two :element-type 'fixnum :initial-element 0))
         (%make-castable kvs (get-internal-real-time) test hash-function)))))
 
 (declaim (inline hash))
 (defun hash (table thing)
   (rehash (funcall (%castable-hasher table) thing)))
 
 ;; Not `int size()` from the original! This is more like HASH-TABLE-SIZE, as
 ;; it is the number of mappings that can be held right now.
 (defun castable-size (table)
   (/ (- (length (%castable-kvs table)) 2) 2))
 
 ;; L281 int size()
 (defun castable-count (table)
   (chm-size (chm (%castable-kvs table))))
 
 (defun castable-test (table)
   (%castable-test table))
 
 (defun castable-hasher (table)
   (%castable-hasher table))
 
 ;; L321 TypeV putIfAbsent(TypeK, TypeV)
 (defun put-if-absent (table key value)
   (multiple-value-bind (out present?)
       (put-if-match table key value TOMBSTONE)
     (declare (ignore out))
     (not present?)))
 ;; Missing: containsValue
 ;; L342 boolean replace(TypeK, TypeV)
 (defun put-if-present (table key value)
   (multiple-value-bind (out present?)
       (put-if-match table key value MATCH-ANY)
     (if present?
         (funcall (%castable-test table) out value)
         nil)))
 ;; L347 boolean replace(TypeK, TypeV, TypeV)
 (defun put-if-equal (table key new-value old-value)
   (multiple-value-bind (out present?)
       (put-if-match table key new-value old-value)
     (if present?
         (funcall (%castable-test table) old-value out)
         nil)))
 ;; Missing: clone
 
 ;; L313 put(TypeK, TypeV)
 (defun (setf getchash) (value key table &key (if-exists :overwrite) (if-does-not-exist :overwrite))
   (ecase if-exists
     (:overwrite
      (ecase if-does-not-exist
        (:overwrite
         (put-if-match table key value NO-MATCH-OLD))
        (:error
         (unless (put-if-present table key value)
           (error "Key does not exist in table.")))
        ((NIL)
         (put-if-present table key value))))
     (:error
      (ecase if-does-not-exist
        (:overwrite
         (unless (put-if-absent table key value)
           (error "Key already exists in table.")))
        (:error
         (error "Key either does or does not exist in table."))
        ((NIL)
         (when (nth-value 1 (getchash key table))
           (error "Key already exists in table.")))))
     ((NIL)
      (ecase if-does-not-exist
        (:overwrite
         (put-if-absent table key value))
        (:error
         (unless (nth-value 1 (getchash key table))
           (error "Key does not exist in table.")))
        ((NIL)
         NIL))))
   value)
 
 (define-compiler-macro (setf getchash) (value key table &key (if-exists :overwrite) (if-does-not-exist :create))
   (let ((v (gensym "VALUE")))
     `(let ((,v ,value))
        ,(ecase if-exists
           (:overwrite
            (ecase if-does-not-exist
              (:create
               `(put-if-match ,table ,key ,v NO-MATCH-OLD))
              (:error
               `(unless (put-if-present ,table ,key ,v)
                  (error "Key does not exist in table.")))
              ((NIL)
               `(put-if-present ,table ,key ,v))))
           (:error
            (ecase if-does-not-exist
              (:create
               `(unless (put-if-absent ,table ,key ,v)
                  (error "Key already exists in table.")))
              (:error
               `(error "Key either does or does not exist in table."))
              ((NIL)
               `(when (nth-value 1 (getchash ,key ,table))
                  (error "Key already exists in table.")))))
           ((NIL)
            (ecase if-does-not-exist
              (:create
               `(put-if-absent ,table ,key ,v))
              (:error
               `(unless (nth-value 1 (getchash ,key ,table))
                  (error "Key does not exist in table.")))
              ((NIL)
               NIL))))
        ,v)))
 
 ;; Close to L329 TypeV remove(Object)
 ;; REMHASH returns true if there was a mapping and false otherwise, but
 ;; remove() returns `null` or the old value.
 (defun remchash (key table)
   (if (eq TOMBSTONE (%put-if-match table (%castable-kvs table) key TOMBSTONE NO-MATCH-OLD))
       NIL
       T))
 
 ;; Close to L334 boolean remove(Object, Object)
 (defun try-remchash (table key val)
   (multiple-value-bind (out present?)
       (put-if-match table key TOMBSTONE val)
     (if present?
         (funcall (%castable-test table) out val)
         nil)))
 ;; L352 TypeV putIfMatch(Object, Object, Object)
 (defun put-if-match (table key new old)
   (let ((res (%put-if-match table (%castable-kvs table) key new old)))
     (assert (not (prime-p res)))
     (assert (not (eq res NO-VALUE)))
     (if (eq res TOMBSTONE)
         (values NIL NIL)
         (values res T))))
 ;; L372 void clear()
 (defun clrchash (table)
   (let ((new (%castable-kvs (make-castable))))
     (loop until (sb-ext:cas (%castable-kvs table) (%castable-kvs table) new))))
 
 (declaim (inline keyeq))
 ;; L467 boolean keyeq(Object, Object, int[], int, int)
 (defun keyeq (k key hashes hash fullhash test)
   (declare (type fixnum hash fullhash))
   (declare (type (function (T T) boolean) test))
   (declare (type (simple-array fixnum (*)) hashes))
   (declare (optimize speed))
   (or (eq k key)
       ;; Key does not match exactly, so try more expensive comparison.
       (and ;; If the hash exists, does it match?
            (or (= (aref hashes hash) 0)
                (= (aref hashes hash) fullhash))
            ;; Avoid testing tombstones
            (not (eq k TOMBSTONE))
            ;; Call test function for real comparison
            (funcall test key k))))
 ;; L502 Object get_impl(NonBlockingHashMap, Object[], Object, int)
 (defun %getchash (table kvs key fullhash)
   (declare (type castable table))
   (declare (type simple-vector kvs))
   (declare (type fixnum fullhash))
   (declare (optimize speed))
   (let* ((len (len kvs))
          (chm (chm kvs))
          (hashes (hashes kvs))
          (idx (logand fullhash (1- len)))
          (test (%castable-test table))
          (reprobe-cnt 0))
     (declare (fixnum reprobe-cnt))
     ;; Spin for a hit
     (loop (let ((k (key kvs idx))
                 (v (val kvs idx)))
             ;; Early table miss
             (when (eq k NO-VALUE) (return NO-VALUE))
             (let ((newkvs (%chm-newkvs chm)))
               ;; Compare the keys
               (when (keyeq k key hashes idx fullhash test)
                 ;; If we are not copying at the moment, we're done.
                 (unless (prime-p v)
                   (return (if (eq v TOMBSTONE)
                               NO-VALUE
                               v)))
                 ;; Copy in progress, help with copying and retry.
                 (return (%getchash table
                                    (copy-slot-and-check chm table kvs idx key)
                                    key
                                    fullhash)))
               ;; If we exceed reprobes, help resizing.
               (when (or (<= (reprobe-limit len) (incf reprobe-cnt))
                         (eq key TOMBSTONE))
                 (if (null newkvs)
                     ;; Nothing here.
                     (return NO-VALUE)
                     ;; Retry in a new table copy
                     (return (%getchash table (help-copy table newkvs) key fullhash))))
               ;; Reprobe.
               (setf idx (logand (1+ idx) (1- len))))))))
 
 ;; L495 TypeV get(Object)
 (defun getchash (key table &optional default)
   (declare (optimize speed))
   (let* ((fullhash (hash table key))
          (value (%getchash table (%castable-kvs table) key fullhash)))
     ;; Make sure we never return primes
     (check-type value (not prime))
     (if (eql value NO-VALUE)
         (values default NIL)
         (values value T))))
 
 ;; L555 Object putIfMatch(NonBlockingHashMap, Object[], Object, Object, Object)
 (defun %put-if-match (table kvs key put exp)
   (declare (type castable table))
   (declare (type simple-vector kvs))
   (declare (optimize speed))
   (assert (and (not (prime-p put))
                (not (prime-p exp))))
   (let* ((fullhash (hash table key))
          (len (len kvs))
          (chm (chm kvs))
          (hashes (hashes kvs))
          (test (%castable-test table))
          (idx (logand fullhash (1- len)))
          (reprobe-cnt 0)
          (k NO-VALUE) (v NO-VALUE)
          (newkvs NIL))
     (declare (type fixnum idx reprobe-cnt))
     ;; Spin for a hit
     (loop (setf v (val kvs idx))
           (setf k (key kvs idx))
           ;; Is the slot free?
           (when (eq k NO-VALUE)
             ;; No need to put a tombstone in an empty field
             (when (eq put TOMBSTONE)
               (return-from %put-if-match put))
             ;; Claim the spot
             (when (cas-key kvs idx NO-VALUE key)
               (incf-counter (%chm-slots chm))
               (setf (aref hashes idx) fullhash)
               (return))
             ;; We failed, update the key
             (setf k (key kvs idx))
             (assert (not (eq k NO-VALUE))))
           ;; Okey, we have a key there
           (setf newkvs (%chm-newkvs chm))
           ;; Test if this is our key
           (when (keyeq k key hashes idx fullhash test)
             (return))
           ;; If we exceed reprobes, start resizing
           (when (or (<= (reprobe-limit len) (incf reprobe-cnt))
                     (eq key TOMBSTONE))
             (setf newkvs (resize chm table kvs))
             (unless (eq exp NO-VALUE) (help-copy table newkvs))
             (return-from %put-if-match
               (%put-if-match table newkvs key put exp)))
           ;; Reprobe.
           (setf idx (logand (1+ idx) (1- len))))
     ;; We found a key slot, time to update it
     ;; Fast-path
     (when (eq put v) (return-from %put-if-match v))
     ;; Check if we want to move to a new table
     (when (and ;; Do we have a new table already?
                (null newkvs)
                ;; Check the value
                (or (and (eq v NO-VALUE) (table-full-p chm reprobe-cnt len))
                    (prime-p v)))
       (setf newkvs (resize chm table kvs)))
     ;; Check if we are indeed moving and retry
     (unless (null newkvs)
       (return-from %put-if-match
         (%put-if-match table (copy-slot-and-check chm table kvs idx exp) key put exp)))
     ;; Finally we can do the update
     (loop (check-type v (not prime))
           ;; If we don't match the old, bail out
           (when (and (not (eq exp NO-MATCH-OLD))
                      (not (eq v exp))
                      (or (not (eq exp MATCH-ANY))
                          (eq v TOMBSTONE)
                          (eq v NO-VALUE))
                      (not (and (eq v NO-VALUE) (eq exp TOMBSTONE)))
                      (or (eq exp NO-VALUE) (not (funcall test exp v))))
             (return v))
           ;; Perform the change
           (when (cas-val kvs idx v put)
             ;; Okey, we got it, update the size
             (unless (eq exp NO-VALUE)
               (when (and (or (eq v NO-VALUE) (eq v TOMBSTONE))
                          (not (eq put TOMBSTONE)))
                 (incf-counter (%chm-size chm)))
               (when (and (not (or (eq v NO-VALUE) (eq v TOMBSTONE)))
                          (eq put TOMBSTONE))
                 (decf-counter (%chm-size chm))))
             (return (if (and (eq v NO-VALUE) (not (eq exp NO-VALUE)))
                         TOMBSTONE
                         v)))
           ;; CAS failed, retry
           (setf v (val kvs idx))
           ;; If we got a prime we need to restart from the beginning
           (when (prime-p v)
             (return (%put-if-match table (copy-slot-and-check chm table kvs idx exp) key put exp))))))
 
 ;; L699 Object[] help_copy(Object[])
 (declaim (inline help-copy))
 (defun help-copy (table helper)
   (declare (type castable table))
   (declare (optimize speed))
   (let* ((topkvs (%castable-kvs table))
          (topchm (chm topkvs)))
     (unless (null (%chm-newkvs topchm))
       (%help-copy topchm table topkvs NIL))
     helper))
 
 ;; L794 Object[] resize(NonBlockingHashMap, Object[])
 (defun resize (chm table kvs)
   (declare (type chm chm))
   (declare (type castable table))
   (declare (type simple-array kvs))
   (declare (optimize speed))
   (assert (eq chm (chm kvs)))
   ;; Check for resize in progress
   (let ((newkvs (%chm-newkvs chm)))
     (unless (null newkvs)
       ;; Use the new table already
       (return-from resize newkvs))
     (let* ((oldlen (len kvs))
            (sz (chm-size chm))
            (newsz sz))
       (declare (type fixnum oldlen sz newsz))
       ;; Heuristic for new size
       (when (<= (ash oldlen -2) sz)
         (setf newsz (ash oldlen 1))
         (when (<= sz (ash oldlen -1))
           (setf newsz (ash oldlen 2))))
       ;; Much denser table with more reprobes
       #+(or)
       (when (<= (ash oldlen -1) sz)
         (setf newsz (ash oldlen 1)))
       ;; Was the last resize recent? If so, double again
       ;; to accommodate tables with lots of inserts at the moment.
       (let ((tm (get-internal-real-time)))
         (when (and (<= newsz oldlen)
                    ;; If we resized less than a second ago
                    (<= tm (+ (%castable-last-resize table)
                              INTERNAL-TIME-UNITS-PER-SECOND))
                    ;; And we have plenty of dead keys
                    (<= (ash sz 1) (counter-value~ (%chm-slots chm))))
           (setf newsz (ash oldlen 1))))
       ;; Don't shrink
       (when (< newsz oldlen) (setf newsz oldlen))
       (let ((size MIN-SIZE)
             (r (%chm-resizers chm)))
         (declare (type fixnum size))
         ;; Convert to power of two
         (loop while (< size newsz)
               do (setf size (ash size 1)))
         ;; Limit the number of threads resizing things
         (loop until (sb-ext:cas (%chm-resizers chm) r (1+ r))
               do (setf r (%chm-resizers chm)))
         ;; Size calculation: 2 words per table + extra
         ;; NOTE: The original assumes 32 bit pointers, we conditionalise
         (let ((megs (ash (ash (+ (* size 2) 4)
                               #+64-BIT 4 #-64-BIT 3)
                          -20)))
           (declare (type fixnum megs))
           (when (and (<= 2 r) (< 0 megs))
             (setf newkvs (%chm-newkvs chm))
             (unless (null newkvs)
               (return-from resize newkvs))
             ;; We already have two threads trying a resize, wait
             (sleep (/ (* 8 megs) 1000))))
         ;; Last check
         (setf newkvs (%chm-newkvs chm))
         (unless (null newkvs)
           (return-from resize newkvs))
         ;; Allocate the array
         (setf newkvs (make-array (+ 2 (* 2 size)) :initial-element NO-VALUE))
         (setf (svref newkvs 0) (make-chm (%chm-size chm)))
         (setf (svref newkvs 1) (make-array size :element-type 'fixnum :initial-element 0))
         ;; Check again after the allocation
         (unless (null (%chm-newkvs chm))
           (return-from resize (%chm-newkvs chm)))
         ;; CAS the table in. We can let the GC handle deallocation. Thanks, GC!
         (if (cas-newkvs chm newkvs)
             newkvs
             (%chm-newkvs chm))))))
 
 ;; L906 help_copy_impl(NonBlockingHashMap, Object[], boolean)
 (defun %help-copy (chm table oldkvs copy-all)
   (declare (type chm chm))
   (declare (type castable table))
   (declare (type simple-array oldkvs))
   (declare (optimize speed))
   (assert (eq chm (chm oldkvs)))
   (let* ((newkvs (%chm-newkvs chm))
          (oldlen (len oldkvs))
          (min-copy-work (min oldlen 1024))
          (panic-start -1)
          (copy-idx -9999))
     (declare (type fixnum oldlen min-copy-work copy-idx panic-start))
     (assert (not (null newkvs)))
     ;; Loop while there's work to be done
     (loop while (< (%chm-copy-done chm) oldlen)
           do ;; We panic if we tried to copy twice and it failed.
           (when (= -1 panic-start)
             (setf copy-idx (%chm-copy-idx chm))
             (loop while (and (< copy-idx (ash oldlen 1))
                              (not (sb-ext:cas (%chm-copy-idx chm) copy-idx (+ copy-idx min-copy-work))))
                   do (setf copy-idx (%chm-copy-idx chm)))
             (unless (< copy-idx (ash oldlen 1))
               (setf panic-start copy-idx)))
           ;; Okey, now perform the copy.
           (let ((workdone 0))
             (declare (type fixnum workdone))
             (dotimes (i min-copy-work)
               (when (copy-slot table (logand (+ copy-idx i) (1- oldlen))
                                oldkvs newkvs)
                 (incf workdone)))
             ;; Promote our work
             (when (plusp workdone)
               (copy-check-and-promote chm table oldkvs workdone))
             (incf copy-idx min-copy-work)
             ;; End early if we shouldn't copy everything.
             (when (and (not copy-all) (= -1 panic-start))
               (return-from %help-copy))))
     ;; Promote again in case we race on end of copy
     (copy-check-and-promote chm table oldkvs 0)))
 
 ;; Copy the slot and check that we have done so successfully.
 ;; L970 Object[] copy_slot_and_check(NonBlockingHashMap, Object[], int, Object)
 (defun copy-slot-and-check (chm table oldkvs idx should-help)
   (declare (type chm chm))
   (declare (type castable table))
   (declare (type simple-array oldkvs))
   (declare (optimize speed))
   (assert (eq chm (chm oldkvs)))
   (let ((newkvs (%chm-newkvs chm)))
     (assert (not (null newkvs)))
     (when (copy-slot table idx oldkvs (%chm-newkvs chm))
       (copy-check-and-promote chm table oldkvs 1))
     (if should-help
         (help-copy table newkvs)
         newkvs)))
 
 ;; L983 copy_check_and_promote(NonBlockingHashMap, Object[], int)
 (defun copy-check-and-promote (chm table oldkvs work-done)
   (declare (type chm chm))
   (declare (type castable table))
   (declare (type simple-array oldkvs))
   (declare (type fixnum work-done))
   (declare (optimize speed))
   (assert (eq chm (chm oldkvs)))
   (let ((oldlen (len oldkvs))
         (copy-done (%chm-copy-done chm)))
     (assert (<= (+ copy-done work-done) oldlen))
     (when (< 0 work-done)
       (loop until (sb-ext:cas (%chm-copy-done chm) copy-done (+ copy-done work-done))
             do (setf copy-done (%chm-copy-done chm))
                (assert (<= (+ copy-done work-done) oldlen))))
     ;; Check for copy being completely done and promote
     (when (and (= (+ copy-done work-done) oldlen)
                (eq (%castable-kvs table) oldkvs)
                (sb-ext:cas (%castable-kvs table) oldkvs (%chm-newkvs chm)))
       (setf (%castable-last-resize table) (get-internal-real-time)))))
 
 ;; Copy one slot into the new table,
 ;; returns true if we are sure that the new table has a value.
 ;; L1023 boolean copy_slot(NonBlockingHashMap, int, Object[], Object[])
 (defun copy-slot (table idx oldkvs newkvs)
   (declare (type castable table))
   (declare (type fixnum idx))
   (declare (type simple-array oldkvs newkvs))
   (declare (optimize speed))
   ;; First tombstone the key blindly.
   (let (key)
     (loop while (eq (setf key (key oldkvs idx)) NO-VALUE)
           do (cas-key oldkvs idx NO-VALUE TOMBSTONE))
     ;; Prevent new values from showing up in the old table
     (let ((oldval (val oldkvs idx)))
       (loop until (prime-p oldval)
             for box = (if (or (eq oldval NO-VALUE)
                               (eq oldval TOMBSTONE))
                           TOMBPRIME
                           (prime oldval))
             do (when (cas-val oldkvs idx oldval box)
                  ;; We made sure to prime the value to prevent updates.
                  (when (eq box TOMBPRIME)
                    (return-from copy-slot T))
                  (setf oldval box)
                  (return))
                ;; Retry on CAS failure
                (setf oldval (val oldkvs idx)))
       (when (eq oldval TOMBPRIME)
         ;; We already completed the copy
         (return-from copy-slot NIL))
       ;; Finally do the actual copy, but only if we would write into
       ;; a null. Otherwise, someone else already copied.
       (let ((old-unboxed (prime-value oldval)))
         (assert (not (eq old-unboxed TOMBSTONE)))
         (prog1 (eq NO-VALUE (%put-if-match table newkvs key old-unboxed NO-VALUE))
           ;; Now that the copy is done, we can stub out the old key completely.
           (loop until (cas-val oldkvs idx oldval TOMBPRIME)
                 do (setf oldval (val oldkvs idx))))))))
 
 (defun mapchash (function table)
   (let (snapshot-kvs)
     (loop for top-kvs = (%castable-kvs table)
           for top-chm = (chm top-kvs)
           for newkvs  = (%chm-newkvs top-chm)
           until (null newkvs)
           do (help-copy table newkvs)
           finally (setf snapshot-kvs top-kvs))
     (loop for position from 2 below (length snapshot-kvs) by 2
           for key   = (aref snapshot-kvs position)
           for value = (aref snapshot-kvs (1+ position))
           unless (or (eq key   NO-VALUE)
                      (eq key   TOMBSTONE)
                      (eq value NO-VALUE))
             do (funcall function key value))))
 
 (defmethod print-object ((table castable) stream)
   (print-unreadable-object (table stream :type t :identity t)
     (format stream ":test ~s :count ~s :size ~s"
             (castable-test table)
             (castable-count table)
             (castable-size table))))