102 lines
2.7 KiB
Scheme
102 lines
2.7 KiB
Scheme
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; Copyright (c) 1993, 1994 Richard Kelsey and Jonathan Rees. See file COPYING.
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; New, more efficient SLEEP 1/23/92
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; Earlier, simpler (and probably better) version:
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;(define (sleep n)
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; (let ((until (+ (time) n)))
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; (with-interrupts-inhibited
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; (lambda ()
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; (let loop ()
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; (if (>= (time) until)
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; #t
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; (begin (dispatch)
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; (loop))))))))
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; NYI: If there are no dozers to awake, and no runnable threads, and
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; we're running under time sharing, we really ought to be polite and
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; relinquish the processor to other processes by doing an appropriate
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; system call (on unix, this means pause, sleep, or select).
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(define (sleep n)
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(let ((cv (make-condvar)))
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(with-lock dozers-lock
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(lambda ()
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(set! *dozers*
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(insert (cons (+ (time) n) cv)
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*dozers*
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(lambda (frob1 frob2)
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(< (car frob1) (car frob2)))))
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(if (not *wakeup-service*)
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(set! *wakeup-service* (spawn wakeup-service 'wakeup-service)))))
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(condvar-ref cv)))
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(define dozers-lock (make-lock))
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(define *dozers* '()) ;List of (wakeup-time . condvar)
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; Wakeup service
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(define *wakeup-service* #f)
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(define (wakeup-service)
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(dynamic-wind
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relinquish-timeslice
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(lambda ()
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(let loop ()
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(obtain-lock dozers-lock)
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(if (not (null? *dozers*))
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(begin (wake-up-some-threads)
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(release-lock dozers-lock)
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(relinquish-timeslice)
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(loop)))))
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(lambda ()
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;; If wakeup service gets killed, propagate kill to the threads
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;; it was going to wake up, so their unwind forms can run.
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(for-each (lambda (dozer)
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(kill-condvar (cdr dozer)))
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*dozers*)
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(set! *dozers* '()) ;in case of kill-thread
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(set! *wakeup-service* #f)
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(if (eq? (lock-owner dozers-lock) (current-thread))
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(release-lock dozers-lock)))))
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(define (wake-up-some-threads)
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(if (null? *dozers*)
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#f
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(if (< (time) (car (car *dozers*)))
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#f
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(let ((cv (cdr (car *dozers*))))
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(set! *dozers* (cdr *dozers*))
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(condvar-set! cv #t)
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(wake-up-some-threads)))))
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(define (insert x l <)
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(cond ((null? l) (list x))
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((< x (car l)) (cons x l))
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(else (cons (car l) (insert x (cdr l) <)))))
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; Real time in seconds since some arbitrary origin.
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(define (time)
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(primitive-time time-option/real-time #f))
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(define primitive-time (structure-ref primitives time))
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(define time-option/real-time (enum time-option real-time))
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(define (read-char-with-timeout port t)
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(with-interrupts-inhibited
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(lambda ()
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(let ((deadline (+ (time) t)))
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(let loop ()
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(cond ((char-ready? port)
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(read-char port))
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((< (time) deadline)
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(dispatch)
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(loop))
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(else 'timeout)))))))
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