17.1.3 Condition Variables

SRFI-18 function: condition-variable? obj

SRFI-18 function: make-condition-variable [name]

SRFI-18 function: condition-variable-name cv

SRFI-18 function: condition-variable-specific cv

SRFI-18 function: condition-variable-specific-set! cv obj

Bigloo function: condition-variable-wait! cv mutex [timeout]

SRFI-18 function: condition-variable-signal! cv

SRFI-18 function: condition-variable-broadcast! cv

(let ((res 0))
   (define (make-semaphore n)
      (vector n (make-mutex) (make-condition-variable)))
   (define (semaphore-wait! sema)
      (mutex-lock! (vector-ref sema 1))
      (let ((n (vector-ref sema 0)))
         (if (> n 0)
             (begin
                (vector-set! sema 0 (- n 1))
                (mutex-unlock! (vector-ref sema 1)))
             (begin
                (condition-variable-wait! (vector-ref sema 2) (vector-ref sema 1))
                (mutex-unlock! (vector-ref sema 1))
                (semaphore-wait! sema)))))
   (define (semaphore-signal-by! sema increment)
      (mutex-lock! (vector-ref sema 1))
      (let ((n (+ (vector-ref sema 0) increment)))
         (vector-set! sema 0 n)
         (if (> n 0)
             (condition-variable-broadcast! (vector-ref sema 2)))
         (mutex-unlock! (vector-ref sema 1))))
   (let ((sema (make-semaphore 10)))
      (let ((t1 (thread-start!
                 (instantiate::thread
                    (body (lambda ()
                             (semaphore-wait! sema)
                             (set! res (current-time)))))))
            (t2 (thread-start!
                 (instantiate::thread
                    (body (lambda ()
                             (let loop ((n 10))
                                (if (> n 0)
                                    (begin
                                       (semaphore-signal-by! sema 1)
                                       (thread-yield!)
                                       (loop (- n 1)))))))))))
         (scheduler-start!)
         res)))
  ⇒ 2

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