src/code/timer.lisp

   1 ;;;; a timer facility based heavily on the timer package by Zach Beane
   2
   3 ;;;; This software is part of the SBCL system. See the README file for
   4 ;;;; more information.
   5 ;;;;
   6 ;;;; This software is derived from the CMU CL system, which was
   7 ;;;; written at Carnegie Mellon University and released into the
   8 ;;;; public domain. The software is in the public domain and is
   9 ;;;; provided with absolutely no warranty. See the COPYING and CREDITS
  10 ;;;; files for more information.
  11
  12 (in-package "SB!IMPL")
  13
  14 ;;; Heap (for the priority queue)
  15
  16 (declaim (inline heap-parent heap-left heap-right))
  17
  18 (defun heap-parent (i)
  19   (ash i -1))
  20
  21 (defun heap-left (i)
  22   (1+ (ash i 1)))
  23
  24 (defun heap-right (i)
  25   (+ 2 (ash i 1)))
  26
  27 (defun heapify (heap start &key (key #'identity) (test #'>=))
  28   (declare (function key test))
  29   (flet ((key (obj) (funcall key obj))
  30          (ge (i j) (funcall test i j)))
  31     (let ((l (heap-left start))
  32           (r (heap-right start))
  33           (size (length heap))
  34           largest)
  35       (setf largest (if (and (< l size)
  36                              (not (ge (key (aref heap start))
  37                                       (key (aref heap l)))))
  38                         l
  39                         start))
  40       (when (and (< r size)
  41                  (not (ge (key (aref heap largest))
  42                           (key (aref heap r)))))
  43         (setf largest r))
  44       (when (/= largest start)
  45         (rotatef (aref heap largest) (aref heap start))
  46         (heapify heap largest :key key :test test)))
  47     heap))
  48
  49 (defun heap-insert (heap new-item &key (key #'identity) (test #'>=))
  50   (declare (function key test))
  51   (flet ((key (obj) (funcall key obj))
  52          (ge (i j) (funcall test i j)))
  53     (vector-push-extend nil heap)
  54     (loop for i = (1- (length heap)) then parent-i
  55           for parent-i = (heap-parent i)
  56           while (and (> i 0)
  57                      (not (ge (key (aref heap parent-i))
  58                               (key new-item))))
  59           do (setf (aref heap i) (aref heap parent-i))
  60           finally (setf (aref heap i) new-item)
  61           (return-from heap-insert i))))
  62
  63 (defun heap-maximum (heap)
  64   (unless (zerop (length heap))
  65     (aref heap 0)))
  66
  67 (defun heap-extract (heap i &key (key #'identity) (test #'>=))
  68   (unless (> (length heap) i)
  69     (error "Heap underflow"))
  70   (prog1
  71       (aref heap i)
  72     (setf (aref heap i) (aref heap (1- (length heap))))
  73     (decf (fill-pointer heap))
  74     (heapify heap i :key key :test test)))
  75
  76 (defun heap-extract-maximum (heap &key (key #'identity) (test #'>=))
  77   (heap-extract heap 0 :key key :test test))
  78
  79 ;;; Priority queue
  80
  81 (defstruct (priority-queue
  82              (:conc-name %pqueue-)
  83              (:constructor %make-priority-queue))
  84   contents
  85   keyfun)
  86
  87 (defun make-priority-queue (&key (key #'identity) (element-type t))
  88   (let ((contents (make-array 100
  89                               :adjustable t
  90                               :fill-pointer 0
  91                               :element-type element-type)))
  92     (%make-priority-queue :keyfun key
  93                           :contents contents)))
  94
  95 (def!method print-object ((object priority-queue) stream)
  96   (print-unreadable-object (object stream :type t :identity t)
  97     (format stream "~[empty~:;~:*~D item~:P~]"
  98             (length (%pqueue-contents object)))))
  99
 100 (defun priority-queue-maximum (priority-queue)
 101   "Return the item in PRIORITY-QUEUE with the largest key."
 102   (symbol-macrolet ((contents (%pqueue-contents priority-queue)))
 103     (unless (zerop (length contents))
 104       (heap-maximum contents))))
 105
 106 (defun priority-queue-extract-maximum (priority-queue)
 107   "Remove and return the item in PRIORITY-QUEUE with the largest key."
 108   (symbol-macrolet ((contents (%pqueue-contents priority-queue))
 109                     (keyfun (%pqueue-keyfun priority-queue)))
 110     (unless (zerop (length contents))
 111       (heap-extract-maximum contents :key keyfun :test #'<=))))
 112
 113 (defun priority-queue-insert (priority-queue new-item)
 114   "Add NEW-ITEM to PRIOIRITY-QUEUE."
 115   (symbol-macrolet ((contents (%pqueue-contents priority-queue))
 116                     (keyfun (%pqueue-keyfun priority-queue)))
 117     (heap-insert contents new-item :key keyfun :test #'<=)))
 118
 119 (defun priority-queue-empty-p (priority-queue)
 120   (zerop (length (%pqueue-contents priority-queue))))
 121
 122 (defun priority-queue-remove (priority-queue item &key (test #'eq))
 123   "Remove and return ITEM from PRIORITY-QUEUE."
 124   (symbol-macrolet ((contents (%pqueue-contents priority-queue))
 125                     (keyfun (%pqueue-keyfun priority-queue)))
 126     (let ((i (position item contents :test test)))
 127       (when i
 128         (heap-extract contents i :key keyfun :test #'<=)
 129         i))))
 130
 131 ;;; thread utility
 132
 133 (defun make-cancellable-interruptor (function)
 134   ;; return a list of two functions: one that does the same as
 135   ;; FUNCTION until the other is called, from when it does nothing.
 136   (let ((mutex (sb!thread:make-mutex))
 137         (cancelled-p nil))
 138     (list
 139      #'(lambda ()
 140          (sb!thread:with-recursive-lock (mutex)
 141            (unless cancelled-p
 142              (funcall function))))
 143      #'(lambda ()
 144          (sb!thread:with-recursive-lock (mutex)
 145            (setq cancelled-p t))))))
 146
 147 ;;; timers
 148
 149 (defstruct (timer
 150              (:conc-name %timer-)
 151              (:constructor %make-timer))
 152   #!+sb-doc
 153   "Timer type. Do not rely on timers being structs as it may change in
 154 future versions."
 155   name
 156   function
 157   expire-time
 158   repeat-interval
 159   (thread nil :type (or sb!thread:thread (member t nil)))
 160   interrupt-function
 161   cancel-function)
 162
 163 (def!method print-object ((timer timer) stream)
 164   (let ((name (%timer-name timer)))
 165     (if name
 166         (print-unreadable-object (timer stream :type t :identity t)
 167           (prin1 name stream))
 168         (print-unreadable-object (timer stream :type t :identity t)
 169           ;; body is empty => there is only one space between type and
 170           ;; identity
 171           ))))
 172
 173 (defun make-timer (function &key name (thread sb!thread:*current-thread*))
 174   #!+sb-doc
 175   "Create a timer object that's when scheduled runs FUNCTION. If
 176 THREAD is a thread then that thread is to be interrupted with
 177 FUNCTION. If THREAD is T then a new thread is created each timer
 178 FUNCTION is run. If THREAD is NIL then FUNCTION can be run in any
 179 thread."
 180   (%make-timer :name name :function function :thread thread))
 181
 182 (defun timer-name (timer)
 183   #!+sb-doc
 184   "Return the name of TIMER."
 185   (%timer-name timer))
 186
 187 (defun timer-scheduled-p (timer &key (delta 0))
 188   #!+sb-doc
 189   "See if TIMER will still need to be triggered after DELTA seconds
 190 from now. For timers with a repeat interval it returns true."
 191   (symbol-macrolet ((expire-time (%timer-expire-time timer))
 192                     (repeat-interval (%timer-repeat-interval timer)))
 193       (or (and repeat-interval (plusp repeat-interval))
 194           (and expire-time
 195                (<= (+ (get-internal-real-time) delta)
 196                    expire-time)))))
 197
 198 ;;; The scheduler
 199
 200 (defvar *scheduler-lock* (sb!thread:make-mutex :name "Scheduler lock"))
 201
 202 (defmacro with-scheduler-lock ((&optional) &body body)
 203   ;; don't let the SIGALRM handler mess things up
 204   `(sb!thread::call-with-system-mutex (lambda () ,@body) *scheduler-lock*))
 205
 206 (defun under-scheduler-lock-p ()
 207   #!-sb-thread
 208   t
 209   #!+sb-thread
 210   (eq sb!thread:*current-thread* (sb!thread:mutex-value *scheduler-lock*)))
 211
 212 (defparameter *schedule* (make-priority-queue :key #'%timer-expire-time))
 213
 214 (defun peek-schedule ()
 215   (priority-queue-maximum *schedule*))
 216
 217 (defun time-left (timer)
 218   (- (%timer-expire-time timer) (get-internal-real-time)))
 219
 220 ;;; real time conversion
 221
 222 (defun delta->real (delta)
 223   (floor (* delta internal-time-units-per-second)))
 224
 225 ;;; Public interface
 226
 227 (defun %schedule-timer (timer)
 228   (let ((changed-p nil)
 229         (old-position (priority-queue-remove *schedule* timer)))
 230     ;; Make sure interruptors are cancelled even if this timer was
 231     ;; scheduled again since our last attempt.
 232     (when old-position
 233       (funcall (%timer-cancel-function timer)))
 234     (when (eql 0 old-position)
 235       (setq changed-p t))
 236     (when (zerop (priority-queue-insert *schedule* timer))
 237       (setq changed-p t))
 238     (setf (values (%timer-interrupt-function timer)
 239                   (%timer-cancel-function timer))
 240           (values-list (make-cancellable-interruptor
 241                         (%timer-function timer))))
 242     (when changed-p
 243       (set-system-timer)))
 244   (values))
 245
 246 (defun schedule-timer (timer time &key repeat-interval absolute-p)
 247   #!+sb-doc
 248   "Schedule TIMER to be triggered at TIME. If ABSOLUTE-P then TIME is
 249 universal time, but non-integral values are also allowed, else TIME is
 250 measured as the number of seconds from the current time. If
 251 REPEAT-INTERVAL is given, TIMER is automatically rescheduled upon
 252 expiry."
 253   ;; CANCEL-FUNCTION may block until all interruptors finish, let's
 254   ;; try to cancel without the scheduler lock first.
 255   (when (%timer-cancel-function timer)
 256     (funcall (%timer-cancel-function timer)))
 257   (with-scheduler-lock ()
 258     (setf (%timer-expire-time timer) (+ (get-internal-real-time)
 259                                         (delta->real
 260                                          (if absolute-p
 261                                              (- time (get-universal-time))
 262                                              time)))
 263           (%timer-repeat-interval timer) (if repeat-interval
 264                                              (delta->real repeat-interval)
 265                                              nil))
 266     (%schedule-timer timer)))
 267
 268 (defun unschedule-timer (timer)
 269   #!+sb-doc
 270   "Cancel TIMER. Once this function returns it is guaranteed that
 271 TIMER shall not be triggered again and there are no unfinished
 272 triggers."
 273   (let ((cancel-function (%timer-cancel-function timer)))
 274     (when cancel-function
 275       (funcall cancel-function)))
 276   (with-scheduler-lock ()
 277     (setf (%timer-expire-time timer) nil
 278           (%timer-repeat-interval timer) nil)
 279     (let ((old-position (priority-queue-remove *schedule* timer)))
 280       (when old-position
 281         (funcall (%timer-cancel-function timer)))
 282       (when (eql 0 old-position)
 283         (set-system-timer))))
 284   (values))
 285
 286 (defun list-all-timers ()
 287   #!+sb-doc
 288   "Return a list of all timers in the system."
 289   (with-scheduler-lock ()
 290     (concatenate 'list (%pqueue-contents *schedule*))))
 291
 292 ;;; Not public, but related
 293
 294 (defun reschedule-timer (timer)
 295   (with-scheduler-lock ()
 296     (setf (%timer-expire-time timer) (+ (get-internal-real-time)
 297                                         (%timer-repeat-interval timer)))
 298     (%schedule-timer timer)))
 299
 300 ;;; Expiring timers
 301
 302 (defun real-time->sec-and-usec(time)
 303   (if (minusp time)
 304       (list 0 1)
 305       (multiple-value-bind (s u) (floor time internal-time-units-per-second)
 306         (setf u (floor (* (/ u internal-time-units-per-second) 1000000)))
 307         (if (= 0 s u)
 308             ;; 0 0 means "shut down the timer" for setitimer
 309             (list 0 1)
 310             (list s u)))))
 311
 312 (defun set-system-timer ()
 313   (assert (under-scheduler-lock-p))
 314   (let ((next-timer (peek-schedule)))
 315     (if next-timer
 316         (let ((delta (- (%timer-expire-time next-timer)
 317                         (get-internal-real-time))))
 318           (apply #'sb!unix:unix-setitimer
 319                  :real 0 0 (real-time->sec-and-usec delta)))
 320         (sb!unix:unix-setitimer :real 0 0 0 0))))
 321
 322 (defun run-timer (timer)
 323   (symbol-macrolet ((function (%timer-function timer))
 324                     (repeat-interval (%timer-repeat-interval timer))
 325                     (thread (%timer-thread timer)))
 326     (when repeat-interval
 327       (reschedule-timer timer))
 328     (cond ((null thread)
 329            (funcall function))
 330           ((eq t thread)
 331            (sb!thread:make-thread function))
 332           (t
 333            (handler-case
 334                (sb!thread:interrupt-thread thread function)
 335              (sb!thread:interrupt-thread-error (c)
 336                (declare (ignore c))
 337                (warn "Timer ~S failed to interrupt thread ~S."
 338                      timer thread)))))))
 339
 340 ;; Called from the signal handler.
 341 (defun run-expired-timers ()
 342   (unwind-protect
 343        (with-interrupts
 344          (let (timer)
 345            (loop
 346             (with-scheduler-lock ()
 347               (setq timer (peek-schedule))
 348               (unless (and timer
 349                            (> (get-internal-real-time)
 350                               (%timer-expire-time timer)))
 351                 (return-from run-expired-timers nil))
 352               (assert (eq timer (priority-queue-extract-maximum *schedule*))))
 353             ;; run the timer without the lock
 354             (run-timer timer))))
 355     (with-scheduler-lock ()
 356       (set-system-timer))))
 357
 358 (defmacro sb!ext:with-timeout (expires &body body)
 359   #!+sb-doc
 360   "Execute the body, asynchronously interrupting it and signalling a TIMEOUT
 361 condition after at least EXPIRES seconds have passed.
 362
 363 Note that it is never safe to unwind from an asynchronous condition. Consider:
 364
 365   (defun call-with-foo (function)
 366     (let (foo)
 367       (unwind-protect
 368          (progn
 369            (setf foo (get-foo))
 370            (funcall function foo))
 371        (when foo
 372          (release-foo foo)))))
 373
 374 If TIMEOUT occurs after GET-FOO has executed, but before the assignment, then
 375 RELEASE-FOO will be missed. While individual sites like this can be made proof
 376 against asynchronous unwinds, this doesn't solve the fundamental issue, as all
 377 the frames potentially unwound through need to be proofed, which includes both
 378 system and application code -- and in essence proofing everything will make
 379 the system uninterruptible."
 380   (with-unique-names (timer)
 381     ;; FIXME: a temporary compatibility workaround for CLX, if unsafe
 382     ;; unwinds are handled revisit it.
 383     `(if (> ,expires 0)
 384          (let ((,timer (make-timer (lambda ()
 385                                      (cerror "Continue" 'sb!ext::timeout)))))
 386            (schedule-timer ,timer ,expires)
 387            (unwind-protect
 388                 (progn ,@body)
 389              (unschedule-timer ,timer)))
 390          (progn ,@body))))