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

;;;; Concurrent ML for Scheme
;;;; SRFI 18: Time Rendezvous

;;; Copyright (c) 2009, Taylor R. Campbell
;;;
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(define (after-time-rendezvous duration-in-milliseconds)

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

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

  (define (block suspension if-enabled if-blocked)
    if-enabled                          ;ignore
    (spawn-timer suspension (/ duration-in-milliseconds 1000))
    (if-blocked))

  (base-rendezvous poll enable block))

(define (at-real-time-rendezvous real-time-in-milliseconds)
  (let ((real-time-in-seconds (/ real-time-in-milliseconds 1000)))

    (define (poll)
      (if (< (time->seconds (current-time)) real-time-in-seconds)
          -1
          #f))

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

    (define (block suspension if-enabled if-blocked)
      ;; Some small amount of time may have passed.  Is this worth
      ;; checking?
      (if (< (time->seconds (current-time)) real-time-in-seconds)
          (begin
            (spawn-timer suspension (seconds->time real-time-in-seconds))
            (if-blocked))
          (if-enabled (lambda () (values)))))

    (base-rendezvous poll enable block)))

(define (spawn-timer suspension timeout)
  ;; It would be nice if we could terminate this thread on negative
  ;; acknowledgement, but the base rendezvous layer doesn't have any
  ;; way to do that at the moment.
  (thread-start!
   (make-thread
    (lambda ()
      (thread-sleep! timeout)
      (maybe-resume suspension (lambda () (values)))))))