src/atimer.c

   1 /* Asynchronous timers.
   2    Copyright (C) 2000-2016 Free Software Foundation, Inc.
   3
   4 This file is part of GNU Emacs.
   5
   6 GNU Emacs is free software: you can redistribute it and/or modify
   7 it under the terms of the GNU General Public License as published by
   8 the Free Software Foundation, either version 3 of the License, or (at
   9 your option) any later version.
  10
  11 GNU Emacs is distributed in the hope that it will be useful,
  12 but WITHOUT ANY WARRANTY; without even the implied warranty of
  13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14 GNU General Public License for more details.
  15
  16 You should have received a copy of the GNU General Public License
  17 along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
  18
  19 #include <config.h>
  20 #include <stdio.h>
  21
  22 #include "lisp.h"
  23 #include "syssignal.h"
  24 #include "systime.h"
  25 #include "atimer.h"
  26 #include <unistd.h>
  27
  28 #ifdef HAVE_TIMERFD
  29 #include <errno.h>
  30 # include <sys/timerfd.h>
  31 #endif
  32
  33 /* Free-list of atimer structures.  */
  34
  35 static struct atimer *free_atimers;
  36
  37 /* List of currently not running timers due to a call to
  38    lock_atimer.  */
  39
  40 static struct atimer *stopped_atimers;
  41
  42 /* List of active atimers, sorted by expiration time.  The timer that
  43    will become ripe next is always at the front of this list.  */
  44
  45 static struct atimer *atimers;
  46
  47 #ifdef HAVE_ITIMERSPEC
  48 /* The alarm timer and whether it was properly initialized, if
  49    POSIX timers are available.  */
  50 static timer_t alarm_timer;
  51 static bool alarm_timer_ok;
  52
  53 # ifdef HAVE_TIMERFD
  54 /* File descriptor for timer, or -1 if it could not be created.  */
  55 static int timerfd;
  56 # else
  57 enum { timerfd = -1 };
  58 # endif
  59 #endif
  60
  61 /* Block/unblock SIGALRM.  */
  62
  63 static void
  64 block_atimers (sigset_t *oldset)
  65 {
  66   sigset_t blocked;
  67   sigemptyset (&blocked);
  68   sigaddset (&blocked, SIGALRM);
  69   sigaddset (&blocked, SIGINT);
  70   pthread_sigmask (SIG_BLOCK, &blocked, oldset);
  71 }
  72 static void
  73 unblock_atimers (sigset_t const *oldset)
  74 {
  75   pthread_sigmask (SIG_SETMASK, oldset, 0);
  76 }
  77
  78 /* Function prototypes.  */
  79
  80 static void set_alarm (void);
  81 static void schedule_atimer (struct atimer *);
  82 static struct atimer *append_atimer_lists (struct atimer *,
  83                                            struct atimer *);
  84
  85 /* Start a new atimer of type TYPE.  TIMESTAMP specifies when the timer is
  86    ripe.  FN is the function to call when the timer fires.
  87    CLIENT_DATA is stored in the client_data member of the atimer
  88    structure returned and so made available to FN when it is called.
  89
  90    If TYPE is ATIMER_ABSOLUTE, TIMESTAMP is the absolute time at which the
  91    timer fires.
  92
  93    If TYPE is ATIMER_RELATIVE, the timer is ripe TIMESTAMP seconds in the
  94    future.
  95
  96    In both cases, the timer is automatically freed after it has fired.
  97
  98    If TYPE is ATIMER_CONTINUOUS, the timer fires every TIMESTAMP seconds.
  99
 100    Value is a pointer to the atimer started.  It can be used in calls
 101    to cancel_atimer; don't free it yourself.  */
 102
 103 struct atimer *
 104 start_atimer (enum atimer_type type, struct timespec timestamp,
 105               atimer_callback fn, void *client_data)
 106 {
 107   struct atimer *t;
 108   sigset_t oldset;
 109
 110   /* Round TIMESTAMP up to the next full second if we don't have itimers.  */
 111 #ifndef HAVE_SETITIMER
 112   if (timestamp.tv_nsec != 0 && timestamp.tv_sec < TYPE_MAXIMUM (time_t))
 113     timestamp = make_timespec (timestamp.tv_sec + 1, 0);
 114 #endif /* not HAVE_SETITIMER */
 115
 116   /* Get an atimer structure from the free-list, or allocate
 117      a new one.  */
 118   if (free_atimers)
 119     {
 120       t = free_atimers;
 121       free_atimers = t->next;
 122     }
 123   else
 124     t = xmalloc (sizeof *t);
 125
 126   /* Fill the atimer structure.  */
 127   memset (t, 0, sizeof *t);
 128   t->type = type;
 129   t->fn = fn;
 130   t->client_data = client_data;
 131
 132   block_atimers (&oldset);
 133
 134   /* Compute the timer's expiration time.  */
 135   switch (type)
 136     {
 137     case ATIMER_ABSOLUTE:
 138       t->expiration = timestamp;
 139       break;
 140
 141     case ATIMER_RELATIVE:
 142       t->expiration = timespec_add (current_timespec (), timestamp);
 143       break;
 144
 145     case ATIMER_CONTINUOUS:
 146       t->expiration = timespec_add (current_timespec (), timestamp);
 147       t->interval = timestamp;
 148       break;
 149     }
 150
 151   /* Insert the timer in the list of active atimers.  */
 152   schedule_atimer (t);
 153   unblock_atimers (&oldset);
 154
 155   /* Arrange for a SIGALRM at the time the next atimer is ripe.  */
 156   set_alarm ();
 157
 158   return t;
 159 }
 160
 161
 162 /* Cancel and free atimer TIMER.  */
 163
 164 void
 165 cancel_atimer (struct atimer *timer)
 166 {
 167   int i;
 168   sigset_t oldset;
 169
 170   block_atimers (&oldset);
 171
 172   for (i = 0; i < 2; ++i)
 173     {
 174       struct atimer *t, *prev;
 175       struct atimer **list = i ? &stopped_atimers : &atimers;
 176
 177       /* See if TIMER is active or stopped.  */
 178       for (t = *list, prev = NULL; t && t != timer; prev = t, t = t->next)
 179         ;
 180
 181       /* If it is, take it off its list, and put in on the free-list.
 182          We don't bother to arrange for setting a different alarm time,
 183          since a too early one doesn't hurt.  */
 184       if (t)
 185         {
 186           if (prev)
 187             prev->next = t->next;
 188           else
 189             *list = t->next;
 190
 191           t->next = free_atimers;
 192           free_atimers = t;
 193           break;
 194         }
 195     }
 196
 197   unblock_atimers (&oldset);
 198 }
 199
 200
 201 /* Append two lists of atimers LIST_1 and LIST_2 and return the
 202    result list.  */
 203
 204 static struct atimer *
 205 append_atimer_lists (struct atimer *list_1, struct atimer *list_2)
 206 {
 207   if (list_1 == NULL)
 208     return list_2;
 209   else if (list_2 == NULL)
 210     return list_1;
 211   else
 212     {
 213       struct atimer *p;
 214
 215       for (p = list_1; p->next; p = p->next)
 216         ;
 217       p->next = list_2;
 218       return list_1;
 219     }
 220 }
 221
 222
 223 /* Stop all timers except timer T.  T null means stop all timers.  */
 224
 225 void
 226 stop_other_atimers (struct atimer *t)
 227 {
 228   sigset_t oldset;
 229   block_atimers (&oldset);
 230
 231   if (t)
 232     {
 233       struct atimer *p, *prev;
 234
 235       /* See if T is active.  */
 236       for (p = atimers, prev = NULL; p && p != t; prev = p, p = p->next)
 237         ;
 238
 239       if (p == t)
 240         {
 241           if (prev)
 242             prev->next = t->next;
 243           else
 244             atimers = t->next;
 245           t->next = NULL;
 246         }
 247       else
 248         /* T is not active.  Let's handle this like T == 0.  */
 249         t = NULL;
 250     }
 251
 252   stopped_atimers = append_atimer_lists (atimers, stopped_atimers);
 253   atimers = t;
 254   unblock_atimers (&oldset);
 255 }
 256
 257
 258 /* Run all timers again, if some have been stopped with a call to
 259    stop_other_atimers.  */
 260
 261 void
 262 run_all_atimers (void)
 263 {
 264   if (stopped_atimers)
 265     {
 266       struct atimer *t = atimers;
 267       struct atimer *next;
 268       sigset_t oldset;
 269
 270       block_atimers (&oldset);
 271       atimers = stopped_atimers;
 272       stopped_atimers = NULL;
 273
 274       while (t)
 275         {
 276           next = t->next;
 277           schedule_atimer (t);
 278           t = next;
 279         }
 280
 281       unblock_atimers (&oldset);
 282     }
 283 }
 284
 285
 286 /* Arrange for a SIGALRM to arrive when the next timer is ripe.  */
 287
 288 static void
 289 set_alarm (void)
 290 {
 291   if (atimers)
 292     {
 293 #ifdef HAVE_SETITIMER
 294       struct itimerval it;
 295 #endif
 296       struct timespec now, interval;
 297
 298 #ifdef HAVE_ITIMERSPEC
 299       if (0 <= timerfd || alarm_timer_ok)
 300         {
 301           struct itimerspec ispec;
 302           ispec.it_value = atimers->expiration;
 303           ispec.it_interval.tv_sec = ispec.it_interval.tv_nsec = 0;
 304 # ifdef HAVE_TIMERFD
 305           if (timerfd_settime (timerfd, TFD_TIMER_ABSTIME, &ispec, 0) == 0)
 306             {
 307               add_timer_wait_descriptor (timerfd);
 308               return;
 309             }
 310 # endif
 311           if (alarm_timer_ok
 312               && timer_settime (alarm_timer, TIMER_ABSTIME, &ispec, 0) == 0)
 313             return;
 314         }
 315 #endif
 316
 317       /* Determine interval till the next timer is ripe.
 318          Don't set the interval to 0; this disables the timer.  */
 319       now = current_timespec ();
 320       interval = (timespec_cmp (atimers->expiration, now) <= 0
 321                   ? make_timespec (0, 1000 * 1000)
 322                   : timespec_sub (atimers->expiration, now));
 323
 324 #ifdef HAVE_SETITIMER
 325
 326       memset (&it, 0, sizeof it);
 327       it.it_value = make_timeval (interval);
 328       setitimer (ITIMER_REAL, &it, 0);
 329 #else /* not HAVE_SETITIMER */
 330       alarm (max (interval.tv_sec, 1));
 331 #endif /* not HAVE_SETITIMER */
 332     }
 333 }
 334
 335
 336 /* Insert timer T into the list of active atimers `atimers', keeping
 337    the list sorted by expiration time.  T must not be in this list
 338    already.  */
 339
 340 static void
 341 schedule_atimer (struct atimer *t)
 342 {
 343   struct atimer *a = atimers, *prev = NULL;
 344
 345   /* Look for the first atimer that is ripe after T.  */
 346   while (a && timespec_cmp (a->expiration, t->expiration) < 0)
 347     prev = a, a = a->next;
 348
 349   /* Insert T in front of the atimer found, if any.  */
 350   if (prev)
 351     prev->next = t;
 352   else
 353     atimers = t;
 354
 355   t->next = a;
 356 }
 357
 358 static void
 359 run_timers (void)
 360 {
 361   struct timespec now = current_timespec ();
 362
 363   while (atimers && timespec_cmp (atimers->expiration, now) <= 0)
 364     {
 365       struct atimer *t = atimers;
 366       atimers = atimers->next;
 367       t->fn (t);
 368
 369       if (t->type == ATIMER_CONTINUOUS)
 370         {
 371           t->expiration = timespec_add (now, t->interval);
 372           schedule_atimer (t);
 373         }
 374       else
 375         {
 376           t->next = free_atimers;
 377           free_atimers = t;
 378         }
 379     }
 380
 381   set_alarm ();
 382 }
 383
 384
 385 /* Signal handler for SIGALRM.  SIGNO is the signal number, i.e.
 386    SIGALRM.  */
 387
 388 static void
 389 handle_alarm_signal (int sig)
 390 {
 391   pending_signals = 1;
 392 }
 393
 394 #ifdef HAVE_TIMERFD
 395
 396 /* Called from wait_reading_process_output when FD, which
 397    should be equal to TIMERFD, is available for reading.  */
 398
 399 void
 400 timerfd_callback (int fd, void *arg)
 401 {
 402   ptrdiff_t nbytes;
 403   uint64_t expirations;
 404
 405   eassert (fd == timerfd);
 406   nbytes = emacs_read (fd, &expirations, sizeof (expirations));
 407
 408   if (nbytes == sizeof (expirations))
 409     {
 410       /* Timer should expire just once.  */
 411       eassert (expirations == 1);
 412       do_pending_atimers ();
 413     }
 414   else if (nbytes < 0)
 415     /* For some not yet known reason, we may get weird event and no
 416        data on timer descriptor.  This can break Gnus at least, see:
 417        http://lists.gnu.org/archive/html/emacs-devel/2014-07/msg00503.html.  */
 418     eassert (errno == EAGAIN);
 419   else
 420     /* I don't know what else can happen with this descriptor.  */
 421     emacs_abort ();
 422 }
 423
 424 #endif /* HAVE_TIMERFD */
 425
 426 /* Do pending timers.  */
 427
 428 void
 429 do_pending_atimers (void)
 430 {
 431   if (atimers)
 432     {
 433       sigset_t oldset;
 434       block_atimers (&oldset);
 435       run_timers ();
 436       unblock_atimers (&oldset);
 437     }
 438 }
 439
 440
 441 /* Turn alarms on/off.  This seems to be temporarily necessary on
 442    some systems like HPUX (see process.c).  */
 443
 444 void
 445 turn_on_atimers (bool on)
 446 {
 447   if (on)
 448     set_alarm ();
 449   else
 450     {
 451 #ifdef HAVE_ITIMERSPEC
 452       struct itimerspec ispec;
 453       memset (&ispec, 0, sizeof ispec);
 454       if (alarm_timer_ok)
 455         timer_settime (alarm_timer, TIMER_ABSTIME, &ispec, 0);
 456 # ifdef HAVE_TIMERFD
 457       timerfd_settime (timerfd, TFD_TIMER_ABSTIME, &ispec, 0);
 458 # endif
 459 #endif
 460       alarm (0);
 461     }
 462 }
 463
 464 /* This is intended to use from automated tests.  */
 465
 466 #ifdef ENABLE_CHECKING
 467
 468 #define MAXTIMERS 10
 469
 470 struct atimer_result
 471 {
 472   /* Time when we expect this timer to trigger.  */
 473   struct timespec expected;
 474
 475   /* Timer status: -1 if not triggered, 0 if triggered
 476      too early or too late, 1 if triggered timely.  */
 477   int intime;
 478 };
 479
 480 static void
 481 debug_timer_callback (struct atimer *t)
 482 {
 483   struct timespec now = current_timespec ();
 484   struct atimer_result *r = (struct atimer_result *) t->client_data;
 485   int result = timespec_cmp (now, r->expected);
 486
 487   if (result < 0)
 488     /* Too early.  */
 489     r->intime = 0;
 490   else if (result >= 0)
 491     {
 492 #ifdef HAVE_SETITIMER
 493       struct timespec delta = timespec_sub (now, r->expected);
 494       /* Too late if later than expected + 0.02s.  FIXME:
 495          this should depend from system clock resolution.  */
 496       if (timespec_cmp (delta, make_timespec (0, 20000000)) > 0)
 497         r->intime = 0;
 498       else
 499 #endif /* HAVE_SETITIMER */
 500         r->intime = 1;
 501     }
 502 }
 503
 504 DEFUN ("debug-timer-check", Fdebug_timer_check, Sdebug_timer_check, 0, 0, 0,
 505        doc: /* Run internal self-tests to check timers subsystem.
 506 Return t if all self-tests are passed, nil otherwise.  */)
 507   (void)
 508 {
 509   int i, ok;
 510   struct atimer *timer;
 511   struct atimer_result *results[MAXTIMERS];
 512   struct timespec t = make_timespec (0, 0);
 513
 514   /* Arm MAXTIMERS relative timers to trigger with 0.1s intervals.  */
 515   for (i = 0; i < MAXTIMERS; i++)
 516     {
 517       results[i] = xmalloc (sizeof (struct atimer_result));
 518       t = timespec_add (t, make_timespec (0, 100000000));
 519       results[i]->expected = timespec_add (current_timespec (), t);
 520       results[i]->intime = -1;
 521       timer = start_atimer (ATIMER_RELATIVE, t,
 522                             debug_timer_callback, results[i]);
 523     }
 524
 525 #ifdef HAVE_TIMERFD
 526   /* Wait for 1s but process timers.  */
 527   wait_reading_process_output (1, 0, 0, false, Qnil, NULL, 0);
 528 #else
 529   /* If timerfd is not supported, wait_reading_process_output won't
 530      pay attention to timers that expired, and the callbacks won't be
 531      called.  So we need to run the expired timers' callbacks by
 532      hand.  */
 533   /* Wait 1.2 sec for the timers to expire.  */
 534   struct timespec tend =
 535     timespec_add (current_timespec (), make_timespec (1, 200000000));
 536
 537   while (timespec_cmp (current_timespec (), tend) < 0)
 538     {
 539       /* Wait for 5 msec between iterations.  */
 540       wait_reading_process_output (0, 5000000, 0, false, Qnil, NULL, 0);
 541       if (pending_signals)
 542         do_pending_atimers ();
 543     }
 544 #endif
 545   /* Shut up the compiler by "using" this variable.  */
 546   (void) timer;
 547
 548   for (i = 0, ok = 0; i < MAXTIMERS; i++)
 549     ok += results[i]->intime, xfree (results[i]);
 550
 551   return ok == MAXTIMERS ? Qt : Qnil;
 552 }
 553
 554 #endif /* ENABLE_CHECKING */
 555
 556 void
 557 init_atimer (void)
 558 {
 559 #ifdef HAVE_ITIMERSPEC
 560 # ifdef HAVE_TIMERFD
 561   /* Until this feature is considered stable, you can ask to not use it.  */
 562   timerfd = (egetenv ("EMACS_IGNORE_TIMERFD") ? -1 :
 563              timerfd_create (CLOCK_REALTIME, TFD_NONBLOCK | TFD_CLOEXEC));
 564 # endif
 565   if (timerfd < 0)
 566     {
 567       struct sigevent sigev;
 568       sigev.sigev_notify = SIGEV_SIGNAL;
 569       sigev.sigev_signo = SIGALRM;
 570       sigev.sigev_value.sival_ptr = &alarm_timer;
 571       alarm_timer_ok
 572         = timer_create (CLOCK_REALTIME, &sigev, &alarm_timer) == 0;
 573     }
 574 #endif
 575   free_atimers = stopped_atimers = atimers = NULL;
 576
 577   /* pending_signals is initialized in init_keyboard.  */
 578   struct sigaction action;
 579   emacs_sigaction_init (&action, handle_alarm_signal);
 580   sigaction (SIGALRM, &action, 0);
 581
 582 #ifdef ENABLE_CHECKING
 583   defsubr (&Sdebug_timer_check);
 584 #endif
 585 }