1 (define (make-serializer)
2   (let ((mutex (make-mutex)))
3     (lambda (p)
4       (define (serialized-p . args)
5 	(mutex 'acqure)
6 	(let ((val (apply p args)))
7 	  (mutex 'release)
8 	  val))
9       serialized-p)))
10 
11 (define (make-mutex)
12   (let ((cell (list false)))
13     (define (the-mutex m)
14       (cond ((eq? m 'acquire)
15 	     (if (test-and-set! cell)
16 		 (the-mutex 'acquire)))
17 	    ((eq? m 'release) (clear! cell))))
18     the-mutex))
19 (define (clear! cell)
20   (set-car! cell false))
21 (define (test-and-set! cell)
22   (if (car cell)
23       true
24       (begin (set-car! cell true)
25 	     false)))