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