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#lang racket
(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 (table)
(random-sleep)
(define forks (list (make-semaphore 1)
(make-semaphore 1)
(make-semaphore 1)
(make-semaphore 1)
(make-semaphore 1)))
(define (pick-fork i)
(random-sleep)
(semaphore-wait (list-ref forks i)))
(define (put-fork i)
(random-sleep)
(semaphore-post (list-ref forks i)))
(define (dispatch m)
(cond [(eq? m 'pick-fork) pick-fork]
[(eq? m 'put-fork) put-fork]
[else (error "Unknown request -- TABLE"
m)]))
dispatch)
(define dtable (table))
(define (philosopher dining-table number)
(define my-turn (make-serializer))
(define (eat)
(display number)
(newline)
((dining-table 'pick-fork) number)
((dining-table 'put-fork) number)
((dining-table 'pick-fork) (modulo (+ number 1) 5))
((dining-table 'put-fork) (modulo (+ number 1) 5)))
(my-turn eat))
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