;;; -*- Mode: Scheme; scheme48-package: rendezvous -*-

;;;; Concurrent ML for Scheme
;;;; Scheme48: Time Rendezvous

;;; Copyright (c) 2009, Taylor R. Campbell
;;;
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(define (after-time-rendezvous duration)
  (make-time-rendezvous (lambda () (+ (real-time) duration))))

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

(define (make-time-rendezvous compute-resumption-time)

  (define (poll)
    (if (> (real-time) (compute-resumption-time))
        -1
        #f))

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

  (define (block suspension if-enabled if-blocked)
    (let ((resumption-time (compute-resumption-time)))
      (if (> (real-time) resumption-time)
          (if-enabled (lambda () (values)))
          (begin
            (register-dozer!
             resumption-time
             ;++ If we lie to Scheme48 that waking this dozer has the
             ;++ effect of resuming a thread, will it get angry? -- we
             ;++ can't know, without actually resuming it, whether it
             ;++ will be resumed.
             (lambda () #t)
             (lambda ()
               (maybe-resume suspension (lambda () (values)))))
            (if-blocked)))))

  (base-rendezvous poll enable block))