emacs/src/atimer.c

/* Asynchronous timers.
   Copyright (C) 2000-2013 Free Software Foundation, Inc.

This file is part of GNU Emacs.

GNU Emacs is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.

GNU Emacs is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */

#include <config.h>
#include <stdio.h>

#include "lisp.h"
#include "syssignal.h"
#include "systime.h"
#include "blockinput.h"
#include "atimer.h"
#include <unistd.h>

/* Free-list of atimer structures.  */

static struct atimer *free_atimers;

/* List of currently not running timers due to a call to
   lock_atimer.  */

static struct atimer *stopped_atimers;

/* List of active atimers, sorted by expiration time.  The timer that
   will become ripe next is always at the front of this list.  */

static struct atimer *atimers;

/* The alarm timer and whether it was properly initialized, if
   POSIX timers are available.  */
#ifdef HAVE_ITIMERSPEC
static timer_t alarm_timer;
static bool alarm_timer_ok;
#endif

/* Block/unblock SIGALRM.  */

static void
sigmask_atimers (int how)
{
  sigset_t blocked;
  sigemptyset (&blocked);
  sigaddset (&blocked, SIGALRM);
  pthread_sigmask (how, &blocked, 0);
}
static void
block_atimers (void)
{
  sigmask_atimers (SIG_BLOCK);
}
static void
unblock_atimers (void)
{
  sigmask_atimers (SIG_UNBLOCK);
}

/* Function prototypes.  */

static void set_alarm (void);
static void schedule_atimer (struct atimer *);
static struct atimer *append_atimer_lists (struct atimer *,
                                           struct atimer *);

/* Start a new atimer of type TYPE.  TIME specifies when the timer is
   ripe.  FN is the function to call when the timer fires.
   CLIENT_DATA is stored in the client_data member of the atimer
   structure returned and so made available to FN when it is called.

   If TYPE is ATIMER_ABSOLUTE, TIME is the absolute time at which the
   timer fires.

   If TYPE is ATIMER_RELATIVE, the timer is ripe TIME s/us in the
   future.

   In both cases, the timer is automatically freed after it has fired.

   If TYPE is ATIMER_CONTINUOUS, the timer fires every TIME s/us.

   Value is a pointer to the atimer started.  It can be used in calls
   to cancel_atimer; don't free it yourself.  */

struct atimer *
start_atimer (enum atimer_type type, EMACS_TIME timestamp, atimer_callback fn,
	      void *client_data)
{
  struct atimer *t;

  /* Round TIME up to the next full second if we don't have
     itimers.  */
#ifndef HAVE_SETITIMER
  if (EMACS_NSECS (timestamp) != 0
      && EMACS_SECS (timestamp) < TYPE_MAXIMUM (time_t))
    timestamp = make_emacs_time (EMACS_SECS (timestamp) + 1, 0);
#endif /* not HAVE_SETITIMER */

  /* Get an atimer structure from the free-list, or allocate
     a new one.  */
  if (free_atimers)
    {
      t = free_atimers;
      free_atimers = t->next;
    }
  else
    t = xmalloc (sizeof *t);

  /* Fill the atimer structure.  */
  memset (t, 0, sizeof *t);
  t->type = type;
  t->fn = fn;
  t->client_data = client_data;

  block_atimers ();

  /* Compute the timer's expiration time.  */
  switch (type)
    {
    case ATIMER_ABSOLUTE:
      t->expiration = timestamp;
      break;

    case ATIMER_RELATIVE:
      t->expiration = add_emacs_time (current_emacs_time (), timestamp);
      break;

    case ATIMER_CONTINUOUS:
      t->expiration = add_emacs_time (current_emacs_time (), timestamp);
      t->interval = timestamp;
      break;
    }

  /* Insert the timer in the list of active atimers.  */
  schedule_atimer (t);
  unblock_atimers ();

  /* Arrange for a SIGALRM at the time the next atimer is ripe.  */
  set_alarm ();

  return t;
}


/* Cancel and free atimer TIMER.  */

void
cancel_atimer (struct atimer *timer)
{
  int i;

  block_atimers ();

  for (i = 0; i < 2; ++i)
    {
      struct atimer *t, *prev;
      struct atimer **list = i ? &stopped_atimers : &atimers;

      /* See if TIMER is active or stopped.  */
      for (t = *list, prev = NULL; t && t != timer; prev = t, t = t->next)
	;

      /* If it is, take it off its list, and put in on the free-list.
	 We don't bother to arrange for setting a different alarm time,
	 since a too early one doesn't hurt.  */
      if (t)
	{
	  if (prev)
	    prev->next = t->next;
	  else
	    *list = t->next;

	  t->next = free_atimers;
	  free_atimers = t;
	  break;
	}
    }

  unblock_atimers ();
}


/* Append two lists of atimers LIST_1 and LIST_2 and return the
   result list.  */

static struct atimer *
append_atimer_lists (struct atimer *list_1, struct atimer *list_2)
{
  if (list_1 == NULL)
    return list_2;
  else if (list_2 == NULL)
    return list_1;
  else
    {
      struct atimer *p;

      for (p = list_1; p->next; p = p->next)
	;
      p->next = list_2;
      return list_1;
    }
}


/* Stop all timers except timer T.  T null means stop all timers.  */

void
stop_other_atimers (struct atimer *t)
{
  block_atimers ();

  if (t)
    {
      struct atimer *p, *prev;

      /* See if T is active.  */
      for (p = atimers, prev = NULL; p && p != t; prev = p, p = p->next)
	;

      if (p == t)
	{
	  if (prev)
	    prev->next = t->next;
	  else
	    atimers = t->next;
	  t->next = NULL;
	}
      else
	/* T is not active.  Let's handle this like T == 0.  */
	t = NULL;
    }

  stopped_atimers = append_atimer_lists (atimers, stopped_atimers);
  atimers = t;
  unblock_atimers ();
}


/* Run all timers again, if some have been stopped with a call to
   stop_other_atimers.  */

void
run_all_atimers (void)
{
  if (stopped_atimers)
    {
      struct atimer *t = atimers;
      struct atimer *next;

      block_atimers ();
      atimers = stopped_atimers;
      stopped_atimers = NULL;

      while (t)
	{
	  next = t->next;
	  schedule_atimer (t);
	  t = next;
	}

      unblock_atimers ();
    }
}


/* Arrange for a SIGALRM to arrive when the next timer is ripe.  */

static void
set_alarm (void)
{
  if (atimers)
    {
#ifdef HAVE_SETITIMER
      struct itimerval it;
#endif
      EMACS_TIME now, interval;

#ifdef HAVE_ITIMERSPEC
      if (alarm_timer_ok)
	{
	  struct itimerspec ispec;
	  ispec.it_value = atimers->expiration;
	  ispec.it_interval.tv_sec = ispec.it_interval.tv_nsec = 0;
	  if (timer_settime (alarm_timer, 0, &ispec, 0) == 0)
	    return;
	}
#endif

      /* Determine interval till the next timer is ripe.
	 Don't set the interval to 0; this disables the timer.  */
      now = current_emacs_time ();
      interval = (EMACS_TIME_LE (atimers->expiration, now)
		  ? make_emacs_time (0, 1000 * 1000)
		  : sub_emacs_time (atimers->expiration, now));

#ifdef HAVE_SETITIMER

      memset (&it, 0, sizeof it);
      it.it_value = make_timeval (interval);
      setitimer (ITIMER_REAL, &it, 0);
#else /* not HAVE_SETITIMER */
      alarm (max (EMACS_SECS (interval), 1));
#endif /* not HAVE_SETITIMER */
    }
}


/* Insert timer T into the list of active atimers `atimers', keeping
   the list sorted by expiration time.  T must not be in this list
   already.  */

static void
schedule_atimer (struct atimer *t)
{
  struct atimer *a = atimers, *prev = NULL;

  /* Look for the first atimer that is ripe after T.  */
  while (a && EMACS_TIME_LT (a->expiration, t->expiration))
    prev = a, a = a->next;

  /* Insert T in front of the atimer found, if any.  */
  if (prev)
    prev->next = t;
  else
    atimers = t;

  t->next = a;
}

static void
run_timers (void)
{
  EMACS_TIME now = current_emacs_time ();

  while (atimers && EMACS_TIME_LE (atimers->expiration, now))
    {
      struct atimer *t = atimers;
      atimers = atimers->next;
      t->fn (t);

      if (t->type == ATIMER_CONTINUOUS)
	{
	  t->expiration = add_emacs_time (now, t->interval);
	  schedule_atimer (t);
	}
      else
	{
	  t->next = free_atimers;
	  free_atimers = t;
	}
    }

  set_alarm ();
}


/* Signal handler for SIGALRM.  SIGNO is the signal number, i.e.
   SIGALRM.  */

static void
handle_alarm_signal (int sig)
{
  pending_signals = 1;
}


/* Do pending timers.  */

void
do_pending_atimers (void)
{
  if (atimers)
    {
      block_atimers ();
      run_timers ();
      unblock_atimers ();
    }
}


/* Turn alarms on/off.  This seems to be temporarily necessary on
   some systems like HPUX (see process.c).  */

void
turn_on_atimers (bool on)
{
  if (on)
    set_alarm ();
  else
    alarm (0);
}


void
init_atimer (void)
{
  struct sigaction action;
#ifdef HAVE_ITIMERSPEC
  struct sigevent sigev;
  sigev.sigev_notify = SIGEV_SIGNAL;
  sigev.sigev_signo = SIGALRM;
  sigev.sigev_value.sival_ptr = &alarm_timer;
  alarm_timer_ok = timer_create (CLOCK_REALTIME, &sigev, &alarm_timer) == 0;
#endif
  free_atimers = stopped_atimers = atimers = NULL;
  /* pending_signals is initialized in init_keyboard.*/
  emacs_sigaction_init (&action, handle_alarm_signal);
  sigaction (SIGALRM, &action, 0);
}