;;; -*- Mode: Scheme -*-

;;;; Concurrent ML for Scheme
;;;; MIT Scheme: Time Rendezvous

;;; Copyright (c) 2009--2010, Taylor R. Campbell
;;;
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;;; modification, are permitted provided that the following conditions
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;;;
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;;;   notice, this list of conditions and the following disclaimer.
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;;;   software without specific prior written permission.
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(declare (usual-integrations))

(define (after-time-rendezvous duration)
  (time-rendezvous (lambda () duration)))

(define (at-real-time-rendezvous time)
  (time-rendezvous (lambda () (- time (real-time-clock)))))

(define (time-rendezvous compute-duration)
  (delayed-rendezvous-with-nack
   (lambda (nack-rv)
     (base-time-rendezvous compute-duration nack-rv))))

(define (base-time-rendezvous compute-duration nack-rv)

  (define (poll)
    (if (positive? (compute-duration))
        #f
        -1))

  (define (enable if-enabled if-disabled)
    if-disabled                         ;ignore
    (if-enabled (lambda () (values))))

  (define (block suspension if-enabled if-blocked)
    (let ((duration (compute-duration)))
      (if (positive? duration)
          (let ((registration
                 (register-timer-event duration
                   (lambda ()
                     (maybe-resume suspension (lambda () (values)))))))
            (spawn (lambda ()
                     (synchronize nack-rv)
                     (deregister-timer-event registration)))
            (if-blocked))
          (if-enabled (lambda () (values))))))

  (base-rendezvous poll enable block))