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|
(define (try-two-ways thunk1 thunk2)
(let ((value) (done? #f))
(let ((thread1
(conspire:make-thread
conspire:runnable
(lambda ()
(set! value (thunk1))
(set! done? #t))))
(thread2
(conspire:make-thread
conspire:runnable
(lambda ()
(set! value (thunk2))
(set! done? #t)))))
(conspire:switch-threads
(lambda () done?))
(conspire:kill-threads
(list thread1 thread2))
value)))
(define (test n1 n2)
(with-conspiracy
(lambda ()
(try-two-ways
(lambda ()
(let lp ((n n1))
(if (= n 0)
'a-done
(begin
(if (= (remainder n 100000) 0)
(begin (display 'a)
(conspire:thread-yield)))
(lp (- n 1))))))
(lambda ()
(let lp ((n n2))
(if (= n 0)
'b-done
(begin
(if (= (remainder n 100000) 0)
(begin (display 'b)
(conspire:thread-yield)))
(lp (- n 1))))))))))
#|
(test 1000000 1200000)
ababababababababababab
;Value: a-done
(test 1200000 1000000)
babababababababababaa
;Value: b-done
|#
(define (test1 n1 n2)
(with-time-sharing-conspiracy
(lambda ()
(try-two-ways
(lambda ()
(let lp ((n n1))
(if (= n 0)
'a-done
(begin
(if (= (remainder n 100000) 0)
(display 'a))
(lp (- n 1))))))
(lambda ()
(let lp ((n n2))
(if (= n 0)
'b-done
(begin
(if (= (remainder n 100000) 0)
(display 'b))
(lp (- n 1))))))))))
#|
(test1 1000000 1200000)
baabbaabbaabbaabbaabb
;Value: a-done
(test1 1200000 1000000)
babaabbaabbaabbaabbaa
;Value: b-done
|#
;;; Interesting example
;;; Suppose we want to search a list, that
;;; may be infinite (circular). We could
;;; use the fast algorithm, but sometimes
;;; go into an infinite loop, or we could
;;; use the slow algorithm that marks the
;;; list (with a hash table) but always
;;; works. If the statistics are right,
;;; a better strategy is to time-share the
;;; two methods and take the one which
;;; finishes first:
(define (safe-mem? item lst)
(let ((table (make-eq-hash-table)))
(let lp ((lst lst))
(if (pair? lst)
(if (hash-table/get table lst #f)
#f ;circular
(if (eq? item (car lst))
#t
(begin
(hash-table/put! table lst #t)
(lp (cdr lst)))))
#f))))
(define (unsafe-mem? item lst)
(let lp ((lst lst))
(if (pair? lst)
(if (eq? item (car lst))
#t
(lp (cdr lst)))
#f)))
#|
(define foo (list 'a 'b 'c 'd))
;Value: foo
(begin (set-cdr! (last-pair foo) foo) 'foo)
;Value: foo
(unsafe-mem? 'b foo)
;Value: #t
(unsafe-mem? 'e foo)
;Quit!
(safe-mem? 'b foo)
;Value: #t
(safe-mem? 'e foo)
;Value: #f
|#
(define (mem? item lst)
(with-time-sharing-conspiracy
(lambda ()
(try-two-ways
(lambda ()
(unsafe-mem? item lst))
(lambda ()
(safe-mem? item lst))))))
#|
(mem? 'b foo)
;Value: #t
(mem? 'e foo)
;Value: #f
|#
|
