src/atimer.c

   1 /* Asynchronous timers.
   2    Copyright (C) 2000-2015 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
   9 (at 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 "blockinput.h"
  26 #include "atimer.h"
  27 #include <unistd.h>
  28
  29 #ifdef HAVE_TIMERFD
  30 #include <errno.h>
  31 # include <sys/timerfd.h>
  32 #endif
  33
  34 /* Free-list of atimer structures.  */
  35
  36 static struct atimer *free_atimers;
  37
  38 /* List of currently not running timers due to a call to
  39    lock_atimer.  */
  40
  41 static struct atimer *stopped_atimers;
  42
  43 /* List of active atimers, sorted by expiration time.  The timer that
  44    will become ripe next is always at the front of this list.  */
  45
  46 static struct atimer *atimers;
  47
  48 #ifdef HAVE_ITIMERSPEC
  49 /* The alarm timer and whether it was properly initialized, if
  50    POSIX timers are available.  */
  51 static timer_t alarm_timer;
  52 static bool alarm_timer_ok;
  53
  54 # ifdef HAVE_TIMERFD
  55 /* File descriptor for timer, or -1 if it could not be created.  */
  56 static int timerfd;
  57 # else
  58 enum { timerfd = -1 };
  59 # endif
  60 #endif
  61
  62 /* Block/unblock SIGALRM.  */
  63
  64 static void
  65 block_atimers (sigset_t *oldset)
  66 {
  67   sigset_t blocked;
  68   sigemptyset (&blocked);
  69   sigaddset (&blocked, SIGALRM);
  70   sigaddset (&blocked, SIGINT);
  71   pthread_sigmask (SIG_BLOCK, &blocked, oldset);
  72 }
  73 static void
  74 unblock_atimers (sigset_t const *oldset)
  75 {
  76   pthread_sigmask (SIG_SETMASK, oldset, 0);
  77 }
  78
  79 /* Function prototypes.  */
  80
  81 static void set_alarm (void);
  82 static void schedule_atimer (struct atimer *);
  83 static struct atimer *append_atimer_lists (struct atimer *,
  84                                            struct atimer *);
  85
  86 /* Start a new atimer of type TYPE.  TIMESTAMP specifies when the timer is
  87    ripe.  FN is the function to call when the timer fires.
  88    CLIENT_DATA is stored in the client_data member of the atimer
  89    structure returned and so made available to FN when it is called.
  90
  91    If TYPE is ATIMER_ABSOLUTE, TIMESTAMP is the absolute time at which the
  92    timer fires.
  93
  94    If TYPE is ATIMER_RELATIVE, the timer is ripe TIMESTAMP seconds in the
  95    future.
  96
  97    In both cases, the timer is automatically freed after it has fired.
  98
  99    If TYPE is ATIMER_CONTINUOUS, the timer fires every TIMESTAMP seconds.
 100
 101    Value is a pointer to the atimer started.  It can be used in calls
 102    to cancel_atimer; don't free it yourself.  */
 103
 104 struct atimer *
 105 start_atimer (enum atimer_type type, struct timespec timestamp,
 106               atimer_callback fn, void *client_data)
 107 {
 108   struct atimer *t;
 109   sigset_t oldset;
 110
 111   /* Round TIMESTAMP up to the next full second if we don't have itimers.  */
 112 #ifndef HAVE_SETITIMER
 113   if (timestamp.tv_nsec != 0 && timestamp.tv_sec < TYPE_MAXIMUM (time_t))
 114     timestamp = make_timespec (timestamp.tv_sec + 1, 0);
 115 #endif /* not HAVE_SETITIMER */
 116
 117   /* Get an atimer structure from the free-list, or allocate
 118      a new one.  */
 119   if (free_atimers)
 120     {
 121       t = free_atimers;
 122       free_atimers = t->next;
 123     }
 124   else
 125     t = xmalloc (sizeof *t);
 126
 127   /* Fill the atimer structure.  */
 128   memset (t, 0, sizeof *t);
 129   t->type = type;
 130   t->fn = fn;
 131   t->client_data = client_data;
 132
 133   block_atimers (&oldset);
 134
 135   /* Compute the timer's expiration time.  */
 136   switch (type)
 137     {
 138     case ATIMER_ABSOLUTE:
 139       t->expiration = timestamp;
 140       break;
 141
 142     case ATIMER_RELATIVE:
 143       t->expiration = timespec_add (current_timespec (), timestamp);
 144       break;
 145
 146     case ATIMER_CONTINUOUS:
 147       t->expiration = timespec_add (current_timespec (), timestamp);
 148       t->interval = timestamp;
 149       break;
 150     }
 151
 152   /* Insert the timer in the list of active atimers.  */
 153   schedule_atimer (t);
 154   unblock_atimers (&oldset);
 155
 156   /* Arrange for a SIGALRM at the time the next atimer is ripe.  */
 157   set_alarm ();
 158
 159   return t;
 160 }
 161
 162
 163 /* Cancel and free atimer TIMER.  */
 164
 165 void
 166 cancel_atimer (struct atimer *timer)
 167 {
 168   int i;
 169   sigset_t oldset;
 170
 171   block_atimers (&oldset);
 172
 173   for (i = 0; i < 2; ++i)
 174     {
 175       struct atimer *t, *prev;
 176       struct atimer **list = i ? &stopped_atimers : &atimers;
 177
 178       /* See if TIMER is active or stopped.  */
 179       for (t = *list, prev = NULL; t && t != timer; prev = t, t = t->next)
 180         ;
 181
 182       /* If it is, take it off its list, and put in on the free-list.
 183          We don't bother to arrange for setting a different alarm time,
 184          since a too early one doesn't hurt.  */
 185       if (t)
 186         {
 187           if (prev)
 188             prev->next = t->next;
 189           else
 190             *list = t->next;
 191
 192           t->next = free_atimers;
 193           free_atimers = t;
 194           break;
 195         }
 196     }
 197
 198   unblock_atimers (&oldset);
 199 }
 200
 201
 202 /* Append two lists of atimers LIST_1 and LIST_2 and return the
 203    result list.  */
 204
 205 static struct atimer *
 206 append_atimer_lists (struct atimer *list_1, struct atimer *list_2)
 207 {
 208   if (list_1 == NULL)
 209     return list_2;
 210   else if (list_2 == NULL)
 211     return list_1;
 212   else
 213     {
 214       struct atimer *p;
 215
 216       for (p = list_1; p->next; p = p->next)
 217         ;
 218       p->next = list_2;
 219       return list_1;
 220     }
 221 }
 222
 223
 224 /* Stop all timers except timer T.  T null means stop all timers.  */
 225
 226 void
 227 stop_other_atimers (struct atimer *t)
 228 {
 229   sigset_t oldset;
 230   block_atimers (&oldset);
 231
 232   if (t)
 233     {
 234       struct atimer *p, *prev;
 235
 236       /* See if T is active.  */
 237       for (p = atimers, prev = NULL; p && p != t; prev = p, p = p->next)
 238         ;
 239
 240       if (p == t)
 241         {
 242           if (prev)
 243             prev->next = t->next;
 244           else
 245             atimers = t->next;
 246           t->next = NULL;
 247         }
 248       else
 249         /* T is not active.  Let's handle this like T == 0.  */
 250         t = NULL;
 251     }
 252
 253   stopped_atimers = append_atimer_lists (atimers, stopped_atimers);
 254   atimers = t;
 255   unblock_atimers (&oldset);
 256 }
 257
 258
 259 /* Run all timers again, if some have been stopped with a call to
 260    stop_other_atimers.  */
 261
 262 void
 263 run_all_atimers (void)
 264 {
 265   if (stopped_atimers)
 266     {
 267       struct atimer *t = atimers;
 268       struct atimer *next;
 269       sigset_t oldset;
 270
 271       block_atimers (&oldset);
 272       atimers = stopped_atimers;
 273       stopped_atimers = NULL;
 274
 275       while (t)
 276         {
 277           next = t->next;
 278           schedule_atimer (t);
 279           t = next;
 280         }
 281
 282       unblock_atimers (&oldset);
 283     }
 284 }
 285
 286
 287 /* Arrange for a SIGALRM to arrive when the next timer is ripe.  */
 288
 289 static void
 290 set_alarm (void)
 291 {
 292   if (atimers)
 293     {
 294 #ifdef HAVE_SETITIMER
 295       struct itimerval it;
 296 #endif
 297       struct timespec now, interval;
 298
 299 #ifdef HAVE_ITIMERSPEC
 300       if (0 <= timerfd || alarm_timer_ok)
 301         {
 302           struct itimerspec ispec;
 303           ispec.it_value = atimers->expiration;
 304           ispec.it_interval.tv_sec = ispec.it_interval.tv_nsec = 0;
 305 # ifdef HAVE_TIMERFD
 306           if (timerfd_settime (timerfd, TFD_TIMER_ABSTIME, &ispec, 0) == 0)
 307             {
 308               add_timer_wait_descriptor (timerfd);
 309               return;
 310             }
 311 # endif
 312           if (alarm_timer_ok
 313               && timer_settime (alarm_timer, TIMER_ABSTIME, &ispec, 0) == 0)
 314             return;
 315         }
 316 #endif
 317
 318       /* Determine interval till the next timer is ripe.
 319          Don't set the interval to 0; this disables the timer.  */
 320       now = current_timespec ();
 321       interval = (timespec_cmp (atimers->expiration, now) <= 0
 322                   ? make_timespec (0, 1000 * 1000)
 323                   : timespec_sub (atimers->expiration, now));
 324
 325 #ifdef HAVE_SETITIMER
 326
 327       memset (&it, 0, sizeof it);
 328       it.it_value = make_timeval (interval);
 329       setitimer (ITIMER_REAL, &it, 0);
 330 #else /* not HAVE_SETITIMER */
 331       alarm (max (interval.tv_sec, 1));
 332 #endif /* not HAVE_SETITIMER */
 333     }
 334 }
 335
 336
 337 /* Insert timer T into the list of active atimers `atimers', keeping
 338    the list sorted by expiration time.  T must not be in this list
 339    already.  */
 340
 341 static void
 342 schedule_atimer (struct atimer *t)
 343 {
 344   struct atimer *a = atimers, *prev = NULL;
 345
 346   /* Look for the first atimer that is ripe after T.  */
 347   while (a && timespec_cmp (a->expiration, t->expiration) < 0)
 348     prev = a, a = a->next;
 349
 350   /* Insert T in front of the atimer found, if any.  */
 351   if (prev)
 352     prev->next = t;
 353   else
 354     atimers = t;
 355
 356   t->next = a;
 357 }
 358
 359 static void
 360 run_timers (void)
 361 {
 362   struct timespec now = current_timespec ();
 363
 364   while (atimers && timespec_cmp (atimers->expiration, now) <= 0)
 365     {
 366       struct atimer *t = atimers;
 367       atimers = atimers->next;
 368       t->fn (t);
 369
 370       if (t->type == ATIMER_CONTINUOUS)
 371         {
 372           t->expiration = timespec_add (now, t->interval);
 373           schedule_atimer (t);
 374         }
 375       else
 376         {
 377           t->next = free_atimers;
 378           free_atimers = t;
 379         }
 380     }
 381
 382   set_alarm ();
 383 }
 384
 385
 386 /* Signal handler for SIGALRM.  SIGNO is the signal number, i.e.
 387    SIGALRM.  */
 388
 389 static void
 390 handle_alarm_signal (int sig)
 391 {
 392   pending_signals = 1;
 393 }
 394
 395 #ifdef HAVE_TIMERFD
 396
 397 /* Called from wait_reading_process_output when FD, which
 398    should be equal to TIMERFD, is available for reading.  */
 399
 400 void
 401 timerfd_callback (int fd, void *arg)
 402 {
 403   ptrdiff_t nbytes;
 404   uint64_t expirations;
 405
 406   eassert (fd == timerfd);
 407   nbytes = emacs_read (fd, &expirations, sizeof (expirations));
 408
 409   if (nbytes == sizeof (expirations))
 410     {
 411       /* Timer should expire just once.  */
 412       eassert (expirations == 1);
 413       do_pending_atimers ();
 414     }
 415   else if (nbytes < 0)
 416     /* For some not yet known reason, we may get weird event and no
 417        data on timer descriptor.  This can break Gnus at least, see:
 418        http://lists.gnu.org/archive/html/emacs-devel/2014-07/msg00503.html.  */
 419     eassert (errno == EAGAIN);
 420   else
 421     /* I don't know what else can happen with this descriptor.  */
 422     emacs_abort ();
 423 }
 424
 425 #endif /* HAVE_TIMERFD */
 426
 427 /* Do pending timers.  */
 428
 429 void
 430 do_pending_atimers (void)
 431 {
 432   if (atimers)
 433     {
 434       sigset_t oldset;
 435       block_atimers (&oldset);
 436       run_timers ();
 437       unblock_atimers (&oldset);
 438     }
 439 }
 440
 441
 442 /* Turn alarms on/off.  This seems to be temporarily necessary on
 443    some systems like HPUX (see process.c).  */
 444
 445 void
 446 turn_on_atimers (bool on)
 447 {
 448   if (on)
 449     set_alarm ();
 450   else
 451     {
 452 #ifdef HAVE_ITIMERSPEC
 453       struct itimerspec ispec;
 454       memset (&ispec, 0, sizeof ispec);
 455       if (alarm_timer_ok)
 456         timer_settime (alarm_timer, TIMER_ABSTIME, &ispec, 0);
 457 # ifdef HAVE_TIMERFD
 458       timerfd_settime (timerfd, TFD_TIMER_ABSTIME, &ispec, 0);
 459 # endif
 460 #endif
 461       alarm (0);
 462     }
 463 }
 464
 465 /* This is intended to use from automated tests.  */
 466
 467 #ifdef ENABLE_CHECKING
 468
 469 #define MAXTIMERS 10
 470
 471 struct atimer_result
 472 {
 473   /* Time when we expect this timer to trigger.  */
 474   struct timespec expected;
 475
 476   /* Timer status: -1 if not triggered, 0 if triggered
 477      too early or too late, 1 if triggered timely.  */
 478   int intime;
 479 };
 480
 481 static void
 482 debug_timer_callback (struct atimer *t)
 483 {
 484   struct timespec now = current_timespec ();
 485   struct atimer_result *r = (struct atimer_result *) t->client_data;
 486   int result = timespec_cmp (now, r->expected);
 487
 488   if (result < 0)
 489     /* Too early.  */
 490     r->intime = 0;
 491   else if (result >= 0)
 492     {
 493 #ifdef HAVE_SETITIMER
 494       struct timespec delta = timespec_sub (now, r->expected);
 495       /* Too late if later than expected + 0.01s.  FIXME:
 496          this should depend from system clock resolution.  */
 497       if (timespec_cmp (delta, make_timespec (0, 10000000)) > 0)
 498         r->intime = 0;
 499       else
 500 #endif /* HAVE_SETITIMER */
 501         r->intime = 1;
 502     }
 503 }
 504
 505 DEFUN ("debug-timer-check", Fdebug_timer_check, Sdebug_timer_check, 0, 0, 0,
 506        doc: /* Run internal self-tests to check timers subsystem.
 507 Return t if all self-tests are passed, nil otherwise.  */)
 508   (void)
 509 {
 510   int i, ok;
 511   struct atimer *timer;
 512   struct atimer_result *results[MAXTIMERS];
 513   struct timespec t = make_timespec (0, 0);
 514
 515   /* Arm MAXTIMERS relative timers to trigger with 0.1s intervals.  */
 516   for (i = 0; i < MAXTIMERS; i++)
 517     {
 518       results[i] = xmalloc (sizeof (struct atimer_result));
 519       t = timespec_add (t, make_timespec (0, 100000000));
 520       results[i]->expected = timespec_add (current_timespec (), t);
 521       results[i]->intime = -1;
 522       timer = start_atimer (ATIMER_RELATIVE, t,
 523                             debug_timer_callback, results[i]);
 524     }
 525
 526   /* Wait for 1s but process timers.  */
 527   wait_reading_process_output (1, 0, 0, false, Qnil, NULL, 0);
 528   /* Shut up the compiler by "using" this variable.  */
 529   (void) timer;
 530
 531   for (i = 0, ok = 0; i < MAXTIMERS; i++)
 532     ok += results[i]->intime, xfree (results[i]);
 533
 534   return ok == MAXTIMERS ? Qt : Qnil;
 535 }
 536
 537 #endif /* ENABLE_CHECKING */
 538
 539 void
 540 init_atimer (void)
 541 {
 542 #ifdef HAVE_ITIMERSPEC
 543 # ifdef HAVE_TIMERFD
 544   /* Until this feature is considered stable, you can ask to not use it.  */
 545   timerfd = (egetenv ("EMACS_IGNORE_TIMERFD") ? -1 :
 546              timerfd_create (CLOCK_REALTIME, TFD_NONBLOCK | TFD_CLOEXEC));
 547 # endif
 548   if (timerfd < 0)
 549     {
 550       struct sigevent sigev;
 551       sigev.sigev_notify = SIGEV_SIGNAL;
 552       sigev.sigev_signo = SIGALRM;
 553       sigev.sigev_value.sival_ptr = &alarm_timer;
 554       alarm_timer_ok
 555         = timer_create (CLOCK_REALTIME, &sigev, &alarm_timer) == 0;
 556     }
 557 #endif
 558   free_atimers = stopped_atimers = atimers = NULL;
 559
 560   /* pending_signals is initialized in init_keyboard.  */
 561   struct sigaction action;
 562   emacs_sigaction_init (&action, handle_alarm_signal);
 563   sigaction (SIGALRM, &action, 0);
 564
 565 #ifdef ENABLE_CHECKING
 566   defsubr (&Sdebug_timer_check);
 567 #endif
 568 }