1 (define (make-semaphore-mtx maximal)
2   (let ((count maximal)
3 	(mutex (make-mutex)))
4     (define (the-sema m)
5       (cond ((eq? m 'release)
6 	     (mutex 'acquire)
7 	     (unless (= count maximal)
8 	       (set! count (+ 1 count)))
9 	     (mutex 'release))
10 	    ((eq? m 'acquire)
11 	     (mutex 'acquire)
12 	     (cond ((> count 0)
13 		    (set! count (- count 1))
14 		    (mutex 'release))
15 		   (else
16 		    (mutex 'release)
17 		    (the-sema 'acquire))))
18 	    (else 
19 	     (error "Unknown request -- " m))))
20     the-sema))