1 files changed, 85 insertions, 0 deletions
diff --git a/semestr-2/racket/l15/solution.rkt b/semestr-2/racket/l15/solution.rkt
new file mode 100644
index 0000000..915502e
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+++ b/semestr-2/racket/l15/solution.rkt
@@ -0,0 +1,85 @@
+#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))
+\ No newline at end of file