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;;;; Copyright (C) 1999, 2000, 2001, 2003, 2006, 2009, 2012, 2015 Free Software Foundation, Inc.
;;;;
;;;; This library is free software; you can redistribute it and/or
;;;; modify it under the terms of the GNU Lesser General Public
;;;; License as published by the Free Software Foundation; either
;;;; version 3 of the License, or (at your option) any later version.
;;;;
;;;; This library is distributed in the hope that it will be useful,
;;;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
;;;; Lesser General Public License for more details.
;;;;
;;;; You should have received a copy of the GNU Lesser General Public
;;;; License along with this library; if not, write to the Free Software
;;;; Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
;;;;
;; There are circularities here; you can't import (oop goops compile)
;; before (oop goops). So when compiling, make sure that things are
;; kosher.
(eval-when (expand) (resolve-module '(oop goops)))
(define-module (oop goops dispatch)
#:use-module (oop goops)
#:use-module (oop goops util)
#:use-module (system base target)
#:export (memoize-method!)
#:no-backtrace)
(define *dispatch-module* (current-module))
;;;
;;; Generic functions have an applicable-methods cache associated with
;;; them. Every distinct set of types that is dispatched through a
;;; generic adds an entry to the cache. This cache gets compiled out to
;;; a dispatch procedure. In steady-state, this dispatch procedure is
;;; never recompiled; but during warm-up there is some churn, both to
;;; the cache and to the dispatch procedure.
;;;
;;; So what is the deal if warm-up happens in a multithreaded context?
;;; There is indeed a window between missing the cache for a certain set
;;; of arguments, and then updating the cache with the newly computed
;;; applicable methods. One of the updaters is liable to lose their new
;;; entry.
;;;
;;; This is actually OK though, because a subsequent cache miss for the
;;; race loser will just cause memoization to try again. The cache will
;;; eventually be consistent. We're not mutating the old part of the
;;; cache, just consing on the new entry.
;;;
;;; It doesn't even matter if the dispatch procedure and the cache are
;;; inconsistent -- most likely the type-set that lost the dispatch
;;; procedure race will simply re-trigger a memoization, but since the
;;; winner isn't in the effective-methods cache, it will likely also
;;; re-trigger a memoization, and the cache will finally be consistent.
;;; As you can see there is a possibility for ping-pong effects, but
;;; it's unlikely given the shortness of the window between slot-set!
;;; invocations. We could add a mutex, but it is strictly unnecessary,
;;; and would add runtime cost and complexity.
;;;
(define (emit-linear-dispatch gf-sym nargs methods free rest?)
(define (gen-syms n stem)
(let lp ((n (1- n)) (syms '()))
(if (< n 0)
syms
(lp (1- n) (cons (gensym stem) syms)))))
(let* ((args (gen-syms nargs "a"))
(types (gen-syms nargs "t")))
(let lp ((methods methods)
(free free)
(exp `(cache-miss ,gf-sym
,(if rest?
`(cons* ,@args rest)
`(list ,@args)))))
(cond
((null? methods)
(values `(,(if rest? `(,@args . rest) args)
(let ,(map (lambda (t a)
`(,t (class-of ,a)))
types args)
,exp))
free))
(else
;; jeez
(let preddy ((free free)
(types types)
(specs (vector-ref (car methods) 1))
(checks '()))
(if (null? types)
(let ((m-sym (gensym "p")))
(lp (cdr methods)
(acons (vector-ref (car methods) 3)
m-sym
free)
`(if (and . ,checks)
,(if rest?
`(apply ,m-sym ,@args rest)
`(,m-sym . ,args))
,exp)))
(let ((var (assq-ref free (car specs))))
(if var
(preddy free
(cdr types)
(cdr specs)
(cons `(eq? ,(car types) ,var)
checks))
(let ((var (gensym "c")))
(preddy (acons (car specs) var free)
(cdr types)
(cdr specs)
(cons `(eq? ,(car types) ,var)
checks))))))))))))
(define (compute-dispatch-procedure gf cache)
(define (scan)
(let lp ((ls cache) (nreq -1) (nrest -1))
(cond
((null? ls)
(collate (make-vector (1+ nreq) '())
(make-vector (1+ nrest) '())))
((vector-ref (car ls) 2) ; rest
(lp (cdr ls) nreq (max nrest (vector-ref (car ls) 0))))
(else ; req
(lp (cdr ls) (max nreq (vector-ref (car ls) 0)) nrest)))))
(define (collate req rest)
(let lp ((ls cache))
(cond
((null? ls)
(emit req rest))
((vector-ref (car ls) 2) ; rest
(let ((n (vector-ref (car ls) 0)))
(vector-set! rest n (cons (car ls) (vector-ref rest n)))
(lp (cdr ls))))
(else ; req
(let ((n (vector-ref (car ls) 0)))
(vector-set! req n (cons (car ls) (vector-ref req n)))
(lp (cdr ls)))))))
(define (emit req rest)
(let ((gf-sym (gensym "g")))
(define (emit-rest n clauses free)
(if (< n (vector-length rest))
(let ((methods (vector-ref rest n)))
(cond
((null? methods)
(emit-rest (1+ n) clauses free))
;; FIXME: hash dispatch
(else
(call-with-values
(lambda ()
(emit-linear-dispatch gf-sym n methods free #t))
(lambda (clause free)
(emit-rest (1+ n) (cons clause clauses) free))))))
(emit-req (1- (vector-length req)) clauses free)))
(define (emit-req n clauses free)
(if (< n 0)
(comp `(lambda ,(map cdr free)
(case-lambda ,@clauses))
(map car free))
(let ((methods (vector-ref req n)))
(cond
((null? methods)
(emit-req (1- n) clauses free))
;; FIXME: hash dispatch
(else
(call-with-values
(lambda ()
(emit-linear-dispatch gf-sym n methods free #f))
(lambda (clause free)
(emit-req (1- n) (cons clause clauses) free))))))))
(emit-rest 0
(if (or (zero? (vector-length rest))
(null? (vector-ref rest 0)))
(list `(args (cache-miss ,gf-sym args)))
'())
(acons gf gf-sym '()))))
(define (comp exp vals)
;; When cross-compiling Guile itself, the native Guile must generate
;; code for the host.
(with-target %host-type
(lambda ()
(let ((p ((@ (system base compile) compile) exp
#:env *dispatch-module*
#:from 'scheme
#:opts '(#:partial-eval? #f #:cse? #f))))
(apply p vals)))))
;; kick it.
(scan))
;; o/~ ten, nine, eight
;; sometimes that's just how it goes
;; three, two, one
;;
;; get out before it blows o/~
;;
(define timer-init 30)
(define (delayed-compile gf)
(let ((timer timer-init))
(lambda args
(set! timer (1- timer))
(cond
((zero? timer)
(let ((dispatch (compute-dispatch-procedure
gf (slot-ref gf 'effective-methods))))
(slot-set! gf 'procedure dispatch)
(apply dispatch args)))
(else
;; interestingly, this catches recursive compilation attempts as
;; well; in that case, timer is negative
(cache-dispatch gf args))))))
(define (cache-dispatch gf args)
(define (map-until n f ls)
(if (or (zero? n) (null? ls))
'()
(cons (f (car ls)) (map-until (1- n) f (cdr ls)))))
(define (equal? x y) ; can't use the stock equal? because it's a generic...
(cond ((pair? x) (and (pair? y)
(eq? (car x) (car y))
(equal? (cdr x) (cdr y))))
((null? x) (null? y))
(else #f)))
(if (slot-ref gf 'n-specialized)
(let ((types (map-until (slot-ref gf 'n-specialized) class-of args)))
(let lp ((cache (slot-ref gf 'effective-methods)))
(cond ((null? cache)
(cache-miss gf args))
((equal? (vector-ref (car cache) 1) types)
(apply (vector-ref (car cache) 3) args))
(else (lp (cdr cache))))))
(cache-miss gf args)))
(define (cache-miss gf args)
(apply (memoize-method! gf args) args))
(define (memoize-effective-method! gf args applicable)
(define (first-n ls n)
(if (or (zero? n) (null? ls))
'()
(cons (car ls) (first-n (cdr ls) (- n 1)))))
(define (parse n ls)
(cond ((null? ls)
(memoize n #f (map class-of args)))
((= n (slot-ref gf 'n-specialized))
(memoize n #t (map class-of (first-n args n))))
(else
(parse (1+ n) (cdr ls)))))
(define (memoize len rest? types)
(let* ((cmethod ((@@ (oop goops) compute-cmethod) applicable types))
(cache (cons (vector len types rest? cmethod)
(slot-ref gf 'effective-methods))))
(slot-set! gf 'effective-methods cache)
(slot-set! gf 'procedure (delayed-compile gf))
cmethod))
(parse 0 args))
;;;
;;; Memoization
;;;
(define (memoize-method! gf args)
(let ((applicable ((if (eq? gf compute-applicable-methods)
%compute-applicable-methods
compute-applicable-methods)
gf args)))
(cond (applicable
(memoize-effective-method! gf args applicable))
(else
(no-applicable-method gf args)))))
(set-procedure-property! memoize-method! 'system-procedure #t)
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