timers.c

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/* Copyright (c) 2016-2019, The Tor Project, Inc. */
/* See LICENSE for licensing information */

/* Notes:
 *
 * Having a way to free all timers on shutdown would free people from the
 * need to track them.  Not sure if that's clever though.
 *
 * In an ideal world, Libevent would just switch to use this backend, and we
 * could throw this file away.  But even if Libevent does switch, we'll be
 * stuck with legacy libevents for some time.
 */

#include "orconfig.h"

#define TOR_TIMERS_PRIVATE

#include "lib/evloop/compat_libevent.h"
#include "lib/evloop/timers.h"
#include "lib/intmath/muldiv.h"
#include "lib/log/log.h"
#include "lib/log/util_bug.h"
#include "lib/malloc/malloc.h"
#include "lib/time/compat_time.h"

#ifdef HAVE_SYS_TIME_H
#include <sys/time.h>
#endif

#ifdef _WIN32
// For struct timeval.
#include <winsock2.h>
#endif

struct timeout_cb {
  timer_cb_fn_t cb;
  void *arg;
};

/*
 * These definitions are for timeouts.c  and timeouts.h.
 */
#ifdef __GNUC__
/* We're not exposing any of the functions outside this file. */
#define TIMEOUT_PUBLIC __attribute__((__unused__)) static
#else
/* We're not exposing any of the functions outside this file. */
#define TIMEOUT_PUBLIC static
#endif /* defined(__GNUC__) */
/* We're not using periodic events. */
#define TIMEOUT_DISABLE_INTERVALS
/* We always know the global_timeouts object, so we don't need each timeout
 * to keep a pointer to it. */
#define TIMEOUT_DISABLE_RELATIVE_ACCESS
/* We're providing our own struct timeout_cb. */
#define TIMEOUT_CB_OVERRIDE
/* We're going to support timers that are pretty far out in advance. Making
 * this big can be inefficient, but having a significant number of timers
 * above TIMEOUT_MAX can also be super-inefficient. Choosing 5 here sets
 * timeout_max to 2^30 ticks, or 29 hours with our value for USEC_PER_TICK */
#define WHEEL_NUM 5
#if SIZEOF_VOID_P == 4
/* On 32-bit platforms, we want to override wheel_bit, so that timeout.c will
 * use 32-bit math. */
#define WHEEL_BIT 5
#endif

#include "ext/timeouts/timeout.c"

static struct timeouts *global_timeouts = NULL;
static struct mainloop_event_t *global_timer_event = NULL;

static monotime_t start_of_time;

#define USEC_PER_TICK 100

#define USEC_PER_SEC 1000000

#define MIN_CHECK_SECONDS 3600

#define MIN_CHECK_TICKS \
  (((timeout_t)MIN_CHECK_SECONDS) * (1000000 / USEC_PER_TICK))

static timeout_t
tv_to_timeout(const struct timeval *tv)
{
  uint64_t usec = tv->tv_usec;
  usec += ((uint64_t)USEC_PER_SEC) * tv->tv_sec;
  return usec / USEC_PER_TICK;
}

static void
timeout_to_tv(timeout_t t, struct timeval *tv_out)
{
  t *= USEC_PER_TICK;
  tv_out->tv_usec = (int)(t % USEC_PER_SEC);
  tv_out->tv_sec = (time_t)(t / USEC_PER_SEC);
}

static void
timer_advance_to_cur_time(const monotime_t *now)
{
  timeout_t cur_tick = CEIL_DIV(monotime_diff_usec(&start_of_time, now),
                                USEC_PER_TICK);
  timeouts_update(global_timeouts, cur_tick);
}

static void
libevent_timer_reschedule(void)
{
  monotime_t now;
  monotime_get(&now);
  timer_advance_to_cur_time(&now);

  timeout_t delay = timeouts_timeout(global_timeouts);

  struct timeval d;
  if (delay > MIN_CHECK_TICKS)
    delay = MIN_CHECK_TICKS;
  timeout_to_tv(delay, &d);
  mainloop_event_schedule(global_timer_event, &d);
}

STATIC void
timers_run_pending(void)
{
  monotime_t now;
  monotime_get(&now);
  timer_advance_to_cur_time(&now);

  tor_timer_t *t;
  while ((t = timeouts_get(global_timeouts))) {
    t->callback.cb(t, t->callback.arg, &now);
  }
}

static void
libevent_timer_callback(mainloop_event_t *ev, void *arg)
{
  (void)ev;
  (void)arg;

  timers_run_pending();

  libevent_timer_reschedule();
}

void
timers_initialize(void)
{
  if (BUG(global_timeouts))
    return; // LCOV_EXCL_LINE

  timeout_error_t err = 0;
  global_timeouts = timeouts_open(0, &err);
  if (!global_timeouts) {
    // LCOV_EXCL_START -- this can only fail on malloc failure.
    log_err(LD_BUG, "Unable to open timer backend: %s", strerror(err));
    tor_assert(0);
    // LCOV_EXCL_STOP
  }

  monotime_init();
  monotime_get(&start_of_time);

  mainloop_event_t *timer_event;
  timer_event = mainloop_event_new(libevent_timer_callback, NULL);
  tor_assert(timer_event);
  global_timer_event = timer_event;

  libevent_timer_reschedule();
}

void
timers_shutdown(void)
{
  if (global_timer_event) {
    mainloop_event_free(global_timer_event);
    global_timer_event = NULL;
  }
  if (global_timeouts) {
    timeouts_close(global_timeouts);
    global_timeouts = NULL;
  }
}

tor_timer_t *
timer_new(timer_cb_fn_t cb, void *arg)
{
  tor_timer_t *t = tor_malloc(sizeof(tor_timer_t));
  timeout_init(t, 0);
  timer_set_cb(t, cb, arg);
  return t;
}

void
timer_free_(tor_timer_t *t)
{
  if (! t)
    return;

  timeouts_del(global_timeouts, t);
  tor_free(t);
}

void
timer_set_cb(tor_timer_t *t, timer_cb_fn_t cb, void *arg)
{
  t->callback.cb = cb;
  t->callback.arg = arg;
}

void
timer_get_cb(const tor_timer_t *t,
             timer_cb_fn_t *cb_out, void **arg_out)
{
  if (cb_out)
    *cb_out = t->callback.cb;
  if (arg_out)
    *arg_out = t->callback.arg;
}

void
timer_schedule(tor_timer_t *t, const struct timeval *tv)
{
  const timeout_t delay = tv_to_timeout(tv);

  monotime_t now;
  monotime_get(&now);
  timer_advance_to_cur_time(&now);

  /* Take the old timeout value. */
  timeout_t to = timeouts_timeout(global_timeouts);

  timeouts_add(global_timeouts, t, delay);

  /* Should we update the libevent timer? */
  if (to <= delay) {
    return; /* we're already going to fire before this timer would trigger. */
  }
  libevent_timer_reschedule();
}

void
timer_disable(tor_timer_t *t)
{
  timeouts_del(global_timeouts, t);
  /* We don't reschedule the libevent timer here, since it's okay if it fires
   * early. */
}