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|
#lang racket
(provide philosopher)
;; Do debugu
(define (run-concurrent . thunks)
(define threads (map thread thunks))
(for-each thread-wait threads))
(define (random-sleep)
(sleep (/ (random) 100)))
(define (with-random-sleep proc)
(lambda args
(random-sleep)
(apply proc args)))
(define (make-serializer)
(define sem (make-semaphore 1))
(lambda (proc)
(lambda args
(semaphore-wait sem)
(define ret (apply proc args))
(semaphore-post sem)
ret)))
(define (make-table)
(define forks (map (lambda (x) (make-semaphore 1)) '(0 1 2 3 4)))
(define (get-fork i)
(list-ref forks i))
(define (pick-fork i)
(random-sleep)
(semaphore-wait (get-fork i)))
(define (put-fork i)
(random-sleep)
(semaphore-post (get-fork i)))
(define (dispatch m)
(cond [(eq? m 'pick-fork) pick-fork]
[(eq? m 'put-fork) put-fork]
[else (error "Unknown request -- MAKE-TABLE" m)]))
dispatch)
;(define dining-table (make-table))
;(define (repeat proc n)
; (if (> n 0)
; (begin
; (proc)
; (repeat proc (- n 1)))
; #f))
;
;(define (hungry nr x)
; (lambda () (repeat (lambda () (philosopher dining-table nr)) x)))
;; Rozwiązanie:
(define forks-sem (map (lambda (x) (make-semaphore 1)) '(0 0 0 0 0)))
(define (get-fork i)
(list-ref forks-sem i))
(define (is-free? i)
(semaphore-try-wait? (get-fork i)))
(define (put-fork dining-table i)
((dining-table 'put-fork) i)
(semaphore-post (get-fork i)))
(define (philosopher dining-table i)
(define left-fork i)
(define right-fork (modulo (+ i 1) 5))
(define (loop)
(if (is-free? left-fork)
(if (is-free? right-fork)
(begin
((dining-table 'pick-fork) left-fork)
((dining-table 'pick-fork) right-fork)
(put-fork dining-table left-fork)
(put-fork dining-table right-fork))
(loop))
(begin
(semaphore-post (get-fork left-fork))
(loop))))
(loop))
|
