93 lines
3.1 KiB
Racket
93 lines
3.1 KiB
Racket
#lang racket/base
|
|
;; Timer driver.
|
|
|
|
;; Uses mutable state internally, but because the scope of the
|
|
;; mutation is limited to each timer process alone, it's easy to show
|
|
;; correct linear use of the various pointers.
|
|
|
|
(require racket/set)
|
|
(require racket/match)
|
|
(require data/heap)
|
|
(require "../main.rkt")
|
|
|
|
(struct pending-timer (deadline label) #:transparent)
|
|
|
|
(provide (struct-out set-timer)
|
|
(struct-out timer-expired)
|
|
spawn-timer-driver)
|
|
|
|
(struct set-timer (label msecs kind) #:prefab)
|
|
(struct timer-expired (label msecs) #:prefab)
|
|
|
|
(define (spawn-timer-driver)
|
|
(define control-ch (make-channel))
|
|
(thread (lambda () (timer-driver-thread-main control-ch)))
|
|
(define (timer-driver e count)
|
|
(match e
|
|
[(message (at-meta (and expiry (timer-expired _ _))))
|
|
(transition (- count 1)
|
|
(list (message expiry)
|
|
(when (= count 1)
|
|
(scn/union (subscription (set-timer ? ? ?))
|
|
(advertisement (timer-expired ? ?))))))]
|
|
[(message (and instruction (set-timer _ _ _)))
|
|
(channel-put control-ch instruction)
|
|
(transition (+ count 1)
|
|
(when (= count 0)
|
|
(scn/union (subscription (set-timer ? ? ?))
|
|
(advertisement (timer-expired ? ?))
|
|
(subscription (timer-expired ? ?) #:meta-level 1))))]
|
|
[_ #f]))
|
|
(spawn timer-driver
|
|
0 ;; initial count
|
|
(scn/union (subscription (set-timer ? ? ?))
|
|
(advertisement (timer-expired ? ?)))))
|
|
|
|
(define (timer-driver-thread-main control-ch)
|
|
(define heap (make-timer-heap))
|
|
(let loop ()
|
|
(sync (match (next-timer heap)
|
|
[#f never-evt]
|
|
[t (handle-evt (timer-evt (pending-timer-deadline t))
|
|
(lambda (now)
|
|
(for-each send-ground-message (fire-timers! heap now))
|
|
(loop)))])
|
|
(handle-evt control-ch
|
|
(match-lambda
|
|
[(set-timer label msecs 'relative)
|
|
(install-timer! heap label (+ (current-inexact-milliseconds) msecs))
|
|
(loop)]
|
|
[(set-timer label msecs 'absolute)
|
|
(install-timer! heap label msecs)
|
|
(loop)]
|
|
['quit (void)])))))
|
|
|
|
(define (make-timer-heap)
|
|
(make-heap (lambda (t1 t2) (<= (pending-timer-deadline t1) (pending-timer-deadline t2)))))
|
|
|
|
(define (next-timer heap)
|
|
(and (positive? (heap-count heap))
|
|
(heap-min heap)))
|
|
|
|
(define (fire-timers! heap now)
|
|
(if (zero? (heap-count heap))
|
|
'()
|
|
(let ((m (heap-min heap)))
|
|
(if (<= (pending-timer-deadline m) now)
|
|
(begin (heap-remove-min! heap)
|
|
(cons (timer-expired (pending-timer-label m) now)
|
|
(fire-timers! heap now)))
|
|
'()))))
|
|
|
|
(define (install-timer! heap label deadline)
|
|
(define now (current-inexact-milliseconds))
|
|
(heap-add! heap (pending-timer deadline label)))
|
|
|
|
;; Racket's alarm-evt is almost the right design for timeouts: its
|
|
;; synchronisation value should be the (or some) value of the clock
|
|
;; after the asked-for time. That way it serves as timeout and
|
|
;; clock-reader in one.
|
|
(define (timer-evt msecs)
|
|
(handle-evt (alarm-evt msecs)
|
|
(lambda (_) (current-inexact-milliseconds))))
|