tor/src/or/hibernate.c

/* Copyright 2004 Roger Dingledine, Nick Mathewson. */
/* See LICENSE for licensing information */
/* $Id$ */
const char hibernate_c_id[] = "$Id$";

/**
 * \file hibernate.c
 * \brief Functions to close listeners, stop allowing new circuits,
 * etc in preparation for closing down or going dormant; and to track
 * bandwidth and time intervals to know when to hibernate and when to
 * stop hibernating.
 **/

/*
hibernating, phase 1:
  - send destroy in response to create cells
  - send end (policy failed) in response to begin cells
  - close an OR conn when it has no circuits

hibernating, phase 2:
  (entered when bandwidth hard limit reached)
  - close all OR/AP/exit conns)
*/

#include "or.h"

#define HIBERNATE_STATE_LIVE 1
#define HIBERNATE_STATE_EXITING 2
#define HIBERNATE_STATE_LOWBANDWIDTH 3
#define HIBERNATE_STATE_DORMANT 4

#define SHUTDOWN_WAIT_LENGTH 30 /* seconds */

static int hibernate_state = HIBERNATE_STATE_LIVE;
/** If are hibernating, when do we plan to wake up? Set to 0 if we
 * aren't hibernating. */
static time_t hibernate_end_time = 0;

typedef enum {
  UNIT_MONTH=1, UNIT_WEEK=2, UNIT_DAY=3,
} time_unit_t;

/* Fields for accounting logic.  Accounting overview:
 *
 * Accounting is designed to ensure that no more than N bytes are sent
 * in either direction over a given interval (currently, one month,
 * starting at 0:00 GMT an arbitrary day within the month).  We could
 * try to do this by choking our bandwidth to a trickle, but that
 * would make our streams useless.  Instead, we estimate what our
 * bandwidth usage will be, and guess how long we'll be able to
 * provide that much bandwidth before hitting our limit.  We then
 * choose a random time within the accounting interval to come up (so
 * that we don't get 50 Tors running on the 1st of the month and none
 * on the 30th).
 *
 * Each interval runs as follows:
 *
 * 1. We guess our bandwidth usage, based on how much we used
 *     last time.  We choose a "wakeup time" within the interval to come up.
 * 2. Until the chosen wakeup time, we hibernate.
 * 3. We come up at the wakeup time, and provide bandwidth until we are
 *    "very close" to running out.
 * 4. Then we go into low-bandwidth mode, and stop accepting new
 *    connections, but provide bandwidth until we run out.
 * 5. Then we hibernate until the end of the interval.
 *
 * If the interval ends before we run out of bandwdith, we go back to
 * step one.
 */

/** How many bytes have we read/written in this accounting interval? */
static uint64_t n_bytes_read_in_interval = 0;
static uint64_t n_bytes_written_in_interval = 0;
/** How many seconds have we been running this interval? */
static uint32_t n_seconds_active_in_interval = 0;
/** When did this accounting interval start? */
static time_t interval_start_time = 0;
/** When will this accounting interval end? */
static time_t interval_end_time = 0;
/** How far into the accounting interval should we hibernate? */
static time_t interval_wakeup_time = 0;
/** How much bandwidth do we 'expect' to use per minute?  (0 if we have no
 * info from the last period.) */
static uint32_t expected_bandwidth_usage = 0;
/** What unit are we using for our accounting? */
static time_unit_t cfg_unit = UNIT_MONTH;
/** How many days,hours,minutes into each unit does our accounting interval
 * start? */
static int cfg_start_day = 0;
static int cfg_start_hour = 0;
static int cfg_start_min = 0;

static void reset_accounting(time_t now);
static int read_bandwidth_usage(void);
static time_t start_of_accounting_period_after(time_t now);
static time_t start_of_accounting_period_containing(time_t now);
static void accounting_set_wakeup_time(void);

/* ************
 * Functions for bandwidth accounting.
 * ************/

/** Configure accounting start/end time settings based on
 * options->AccountingStart.  Return 0 on success, -1 on failure. If
 * <b>validate_only</b> is true, do not change the current settings. */
int
accounting_parse_options(or_options_t *options, int validate_only)
{
  time_unit_t unit;
  int ok, idx;
  long d,h,m;
  smartlist_t *items;
  const char *v = options->AccountingStart;
  const char *s;
  char *cp;

  if (!v) {
    if (!validate_only) {
      cfg_unit = UNIT_MONTH;
      cfg_start_day = 1;
      cfg_start_hour = 0;
      cfg_start_min = 0;
    }
    return 0;
  }

  items = smartlist_create();
  smartlist_split_string(items, v, " ", SPLIT_SKIP_SPACE|SPLIT_IGNORE_BLANK,0);
  if (smartlist_len(items)<2) {
    log_fn(LOG_WARN, "Too few arguments to AccountingStart");
    goto err;
  }
  s = smartlist_get(items,0);
  if (0==strcasecmp(s, "month")) {
    unit = UNIT_MONTH;
  } else if (0==strcasecmp(s, "week")) {
    unit = UNIT_WEEK;
  } else if (0==strcasecmp(s, "day")) {
    unit = UNIT_DAY;
  } else {
    log_fn(LOG_WARN, "Unrecognized accounting unit '%s': only 'month', 'week', and 'day' are supported.", s);
    goto err;
  }

  switch (unit) {
  case UNIT_WEEK:
    d = tor_parse_long(smartlist_get(items,1), 10, 1, 7, &ok, NULL);
    if (!ok) {
      log_fn(LOG_WARN, "Weekly accounting must start begin on a day between 1(Monday) and 7 (Sunday)");
      goto err;
    }
    break;
  case UNIT_MONTH:
    d = tor_parse_long(smartlist_get(items,1), 10, 1, 28, &ok, NULL);
    if (!ok) {
      log_fn(LOG_WARN, "Monthy accounting must start begin on a day between 1 and 28");
      goto err;
    }
    break;
  case UNIT_DAY:
    d = 0;
    break;
  default:
    tor_assert(0);
  }

  idx = unit==UNIT_DAY?1:2;
  if (smartlist_len(items) != (idx+1)) {
    log_fn(LOG_WARN, "Accounting unit '%s' requires %d arguments",
           s, idx+1);
    goto err;
  }
  s = smartlist_get(items, idx);
  h = tor_parse_long(s, 10, 0, 23, &ok, &cp);
  if (!ok) {
    log_fn(LOG_WARN, "Accounting start time not parseable: bad hour.");
    goto err;
  }
  if (!cp || *cp!=':') {
    log_fn(LOG_WARN,"Accounting start time not parseable: not in HH:MM format");
    goto err;
  }
  m = tor_parse_long(cp+1, 10, 0, 59, &ok, &cp);
  if (!ok) {
    log_fn(LOG_WARN, "Accounting start time not parseable: bad minute");
    goto err;
  }
  if (!cp || *cp!='\0') {
    log_fn(LOG_WARN,"Accounting start time not parseable: not in HH:MM format");
    goto err;
  }

  if (!validate_only) {
    cfg_unit = unit;
    cfg_start_day = (int)d;
    cfg_start_hour = (int)h;
    cfg_start_min = (int)m;
  }
  SMARTLIST_FOREACH(items, char *, s, tor_free(s));
  smartlist_free(items);
  return 0;
 err:
  SMARTLIST_FOREACH(items, char *, s, tor_free(s));
  smartlist_free(items);
  return -1;
}

/** If we want to manage the accounting system and potentially
 * hibernate, return 1, else return 0.
 */
int accounting_is_enabled(or_options_t *options) {
  if (options->AccountingMax)
    return 1;
  return 0;
}

/** Called from main.c to tell us that <b>seconds</b> seconds have
 * passed, <b>n_read</b> bytes have been read, and <b>n_written</b>
 * bytes have been written. */
void
accounting_add_bytes(size_t n_read, size_t n_written, int seconds)
{
  n_bytes_read_in_interval += n_read;
  n_bytes_written_in_interval += n_written;
  /* If we haven't been called in 10 seconds, we're probably jumping
   * around in time. */
  n_seconds_active_in_interval += (seconds < 10) ? seconds : 0;
}

/** If get_end, return the end of the accounting period that contains
 * the time <b>now</b>.  Else, return the start of the accounting
 * period that contains the time <b>now</b> */
static time_t
edge_of_accounting_period_containing(time_t now, int get_end)
{
  int before;
  struct tm *tm;
  tm = localtime(&now);

  /* Set 'before' to true iff the current time is before the hh:mm
   * changeover time for today. */
  before = tm->tm_hour < cfg_start_hour ||
    (tm->tm_hour == cfg_start_hour && tm->tm_min < cfg_start_min);

  /* Dispatch by unit.  First, find the start day of the given period;
   * then, if get_end is true, increment to the end day. */
  switch (cfg_unit)
    {
    case UNIT_MONTH: {
      /* If this is before the Nth, we want the Nth of last month. */
      if (tm->tm_mday < cfg_start_day ||
          (tm->tm_mday < cfg_start_day && before)) {
        --tm->tm_mon;
      }
      /* Otherwise, the month is correct. */
      tm->tm_mday = cfg_start_day;
      if (get_end)
        ++tm->tm_mon;
      break;
    }
    case UNIT_WEEK: {
      /* What is the 'target' day of the week in struct tm format? (We
         say Sunday==7; struct tm says Sunday==0.) */
      int wday = cfg_start_day % 7;
      /* How many days do we subtract from today to get to the right day? */
      int delta = (7+tm->tm_wday-wday)%7;
      /* If we are on the right day, but the changeover hasn't happened yet,
       * then subtract a whole week. */
      if (delta == 0 && before)
        delta = 7;
      tm->tm_mday -= delta;
      if (get_end)
        tm->tm_mday += 7;
      break;
    }
    case UNIT_DAY:
      if (before)
        --tm->tm_mday;
      if (get_end)
        ++tm->tm_mday;
      break;
    default:
      tor_assert(0);
  }

  tm->tm_hour = cfg_start_hour;
  tm->tm_min = cfg_start_min;
  tm->tm_sec = 0;
  tm->tm_isdst = -1; /* Autodetect DST */
  return mktime(tm);
}

/** Return the start of the accounting period containing the time
 * <b>now</b>. */
static time_t
start_of_accounting_period_containing(time_t now)
{
  return edge_of_accounting_period_containing(now, 0);
}

/** Return the start of the accounting period that comes after the one
 * containing the time <b>now</b>. */
static time_t
start_of_accounting_period_after(time_t now)
{
  return edge_of_accounting_period_containing(now, 1);
}

/** Initialize the accounting subsystem. */
void
configure_accounting(time_t now)
{
  /* Try to remember our recorded usage. */
  if (!interval_start_time)
    read_bandwidth_usage(); /* If we fail, we'll leave values at zero, and
                             * reset below.*/
  if (!interval_start_time ||
      start_of_accounting_period_after(interval_start_time) <= now) {
    /* We didn't have recorded usage, or we don't have recorded usage
     * for this interval. Start a new interval. */
    log_fn(LOG_INFO, "Starting new accounting interval.");
    reset_accounting(now);
  } else if (interval_start_time ==
        start_of_accounting_period_containing(interval_start_time)) {
    log_fn(LOG_INFO, "Continuing accounting interval.");
    /* We are in the interval we thought we were in. Do nothing.*/
    interval_end_time = start_of_accounting_period_after(interval_start_time);
  } else {
    log_fn(LOG_WARN, "Mismatched accounting interval; starting a fresh one.");
    reset_accounting(now);
  }
  accounting_set_wakeup_time();
}

/** Set expected_bandwidth_usage based on how much we sent/received
 * per minute last interval (if we were up for at least 30 minutes),
 * or based on our declared bandwidth otherwise. */
static void
update_expected_bandwidth(void)
{
  uint64_t used, expected;
  uint64_t max_configured = (get_options()->BandwidthRate * 60);

  if (n_seconds_active_in_interval < 1800) {
    /* If we haven't gotten enough data last interval, set 'expected'
     * to 0.  This will set our wakeup to the start of the interval.
     * Next interval, we'll choose our starting time based on how much
     * we sent this interval.
     */
    expected = 0;
  } else {
    used = n_bytes_written_in_interval < n_bytes_read_in_interval ?
      n_bytes_read_in_interval : n_bytes_written_in_interval;
    expected = used / (n_seconds_active_in_interval / 60);
    if (expected > max_configured)
      expected = max_configured;
  }
  if (expected > UINT32_MAX)
    expected = UINT32_MAX;
  expected_bandwidth_usage = (uint32_t) expected;
}

/** Called at the start of a new accounting interval: reset our
 * expected bandwidth usage based on what happened last time, set up
 * the start and end of the interval, and clear byte/time totals.
 */
static void
reset_accounting(time_t now) {
  log_fn(LOG_INFO, "Starting new accounting interval.");
  update_expected_bandwidth();
  interval_start_time = start_of_accounting_period_containing(now);
  interval_end_time = start_of_accounting_period_after(interval_start_time);
  n_bytes_read_in_interval = 0;
  n_bytes_written_in_interval = 0;
  n_seconds_active_in_interval = 0;
}

/** Return true iff we should save our bandwidth usage to disk. */
static INLINE int
time_to_record_bandwidth_usage(time_t now)
{
  /* Note every 60 sec */
#define NOTE_INTERVAL (60)
  /* Or every 20 megabytes */
#define NOTE_BYTES 20*(1024*1024)
  static uint64_t last_read_bytes_noted = 0;
  static uint64_t last_written_bytes_noted = 0;
  static time_t last_time_noted = 0;

  if (last_time_noted + NOTE_INTERVAL <= now ||
      last_read_bytes_noted + NOTE_BYTES <= n_bytes_read_in_interval ||
      last_written_bytes_noted + NOTE_BYTES <= n_bytes_written_in_interval ||
      (interval_end_time && interval_end_time <= now)) {
    last_time_noted = now;
    last_read_bytes_noted = n_bytes_read_in_interval;
    last_written_bytes_noted = n_bytes_written_in_interval;
    return 1;
  }
  return 0;
}

void
accounting_run_housekeeping(time_t now)
{
  if (now >= interval_end_time) {
    configure_accounting(now);
  }
  if (time_to_record_bandwidth_usage(now)) {
    if (accounting_record_bandwidth_usage(now)) {
      log_fn(LOG_ERR, "Couldn't record bandwidth usage; exiting.");
      exit(1);
    }
  }
}

/** Based on our interval and our estimated bandwidth, choose a
 * deterministic (but random-ish) time to wake up. */
static void
accounting_set_wakeup_time(void)
{
  char buf[ISO_TIME_LEN+1];
  char digest[DIGEST_LEN];
  crypto_digest_env_t *d_env;
  int time_in_interval;
  int time_to_exhaust_bw;
  int time_to_consider;

  if (! identity_key_is_set()) {
    if (init_keys() < 0) {
      log_fn(LOG_ERR, "Error initializing keys");
      tor_assert(0);
    }
  }

  format_iso_time(buf, interval_start_time);
  crypto_pk_get_digest(get_identity_key(), digest);

  d_env = crypto_new_digest_env();
  crypto_digest_add_bytes(d_env, buf, ISO_TIME_LEN);
  crypto_digest_add_bytes(d_env, digest, DIGEST_LEN);
  crypto_digest_get_digest(d_env, digest, DIGEST_LEN);
  crypto_free_digest_env(d_env);

  if (!expected_bandwidth_usage) {
    char buf1[ISO_TIME_LEN+1];
    char buf2[ISO_TIME_LEN+1];
    format_local_iso_time(buf1, interval_start_time);
    format_local_iso_time(buf2, interval_end_time);
    time_to_exhaust_bw = 24*60*60;
    interval_wakeup_time = interval_start_time;

    log_fn(LOG_NOTICE, "Configured hibernation.  This interval begins at %s "
        "and ends at %s.  We have no prior estimate for bandwidth, so "
        "we will start out awake and hibernate when we exhaust our bandwidth.",
        buf1, buf2);
    return;
  }

  time_to_exhaust_bw = (int)
    (get_options()->AccountingMax/expected_bandwidth_usage)*60;
  time_in_interval = interval_end_time - interval_start_time;
  time_to_consider = time_in_interval - time_to_exhaust_bw;

  if (time_to_consider<=0) {
    interval_wakeup_time = interval_start_time;
  } else {
    /* XXX can we simplify this just by picking a random (non-deterministic)
     * time to be up? If we go down and come up, then we pick a new one. Is
     * that good enough? -RD */

    /* This is not a perfectly unbiased conversion, but it is good enough:
     * in the worst case, the first half of the day is 0.06 percent likelier
     * to be chosen than the last half. */
    interval_wakeup_time = interval_start_time +
      (get_uint32(digest) % time_to_consider);

    format_iso_time(buf, interval_wakeup_time);
  }

  {
    char buf1[ISO_TIME_LEN+1];
    char buf2[ISO_TIME_LEN+1];
    char buf3[ISO_TIME_LEN+1];
    char buf4[ISO_TIME_LEN+1];
    time_t down_time = interval_wakeup_time+time_to_exhaust_bw;
    if (down_time>interval_end_time)
      down_time = interval_end_time;
    format_local_iso_time(buf1, interval_start_time);
    format_local_iso_time(buf2, interval_wakeup_time);
    format_local_iso_time(buf3,
                   down_time<interval_end_time?down_time:interval_end_time);
    format_local_iso_time(buf4, interval_end_time);

    log_fn(LOG_NOTICE, "Configured hibernation.  This interval began at %s; "
           "the scheduled wake-up time %s %s; "
           "we expect%s to exhaust our bandwidth for this interval around %s; "
           "the next interval begins at %s (all times local)",
           buf1,
           time(NULL)<interval_wakeup_time?"is":"was", buf2,
           time(NULL)<down_time?"":"ed", buf3,
           buf4);
  }
}

#define BW_ACCOUNTING_VERSION 1
/** Save all our bandwidth tracking information to disk. Return 0 on
 * success, -1 on failure*/
int
accounting_record_bandwidth_usage(time_t now)
{
  char buf[128];
  char fname[512];
  char time1[ISO_TIME_LEN+1];
  char time2[ISO_TIME_LEN+1];
  char *cp = buf;
  /* Format is:
     Version\nTime\nTime\nRead\nWrite\nSeconds\nExpected-Rate\n */

  format_iso_time(time1, interval_start_time);
  format_iso_time(time2, now);
  tor_snprintf(cp, sizeof(buf),
               "%d\n%s\n%s\n"U64_FORMAT"\n"U64_FORMAT"\n%lu\n%lu\n",
               BW_ACCOUNTING_VERSION,
               time1,
               time2,
               U64_PRINTF_ARG(n_bytes_read_in_interval),
               U64_PRINTF_ARG(n_bytes_written_in_interval),
               (unsigned long)n_seconds_active_in_interval,
               (unsigned long)expected_bandwidth_usage);
  tor_snprintf(fname, sizeof(fname), "%s/bw_accounting",
               get_options()->DataDirectory);

  return write_str_to_file(fname, buf, 0);
}

/** Read stored accounting information from disk. Return 0 on success;
 * return -1 and change nothing on failure. */
static int
read_bandwidth_usage(void)
{
  char *s = NULL;
  char fname[512];
  time_t t1, t2;
  uint64_t n_read, n_written;
  uint32_t expected_bw, n_seconds;
  smartlist_t *elts;
  int ok;

  tor_snprintf(fname, sizeof(fname), "%s/bw_accounting",
               get_options()->DataDirectory);
  if (!(s = read_file_to_str(fname, 0))) {
    return 0;
  }
  elts = smartlist_create();
  smartlist_split_string(elts, s, "\n", SPLIT_SKIP_SPACE|SPLIT_IGNORE_BLANK,0);
  tor_free(s);

  if (smartlist_len(elts)<1 ||
      atoi(smartlist_get(elts,0)) != BW_ACCOUNTING_VERSION) {
    log_fn(LOG_WARN, "Unrecognized bw_accounting file version: %s",
           (const char*)smartlist_get(elts,0));
    goto err;
  }
  if (smartlist_len(elts) < 7) {
    log_fn(LOG_WARN, "Corrupted bw_accounting file: %d lines",
           smartlist_len(elts));
    goto err;
  }
  if (parse_iso_time(smartlist_get(elts,1), &t1)) {
    log_fn(LOG_WARN, "Error parsing bandwidth usage start time.");
    goto err;
  }
  if (parse_iso_time(smartlist_get(elts,2), &t2)) {
    log_fn(LOG_WARN, "Error parsing bandwidth usage last-written time");
    goto err;
  }
  n_read = tor_parse_uint64(smartlist_get(elts,3), 10, 0, UINT64_MAX,
                            &ok, NULL);
  if (!ok) {
    log_fn(LOG_WARN, "Error parsing number of bytes read");
    goto err;
  }
  n_written = tor_parse_uint64(smartlist_get(elts,4), 10, 0, UINT64_MAX,
                               &ok, NULL);
  if (!ok) {
    log_fn(LOG_WARN, "Error parsing number of bytes read");
    goto err;
  }
  n_seconds = (uint32_t)tor_parse_ulong(smartlist_get(elts,5), 10,0,ULONG_MAX,
                                        &ok, NULL);
  if (!ok) {
    log_fn(LOG_WARN, "Error parsing number of seconds live");
    goto err;
  }
  expected_bw =(uint32_t)tor_parse_ulong(smartlist_get(elts,6), 10,0,ULONG_MAX,
                                        &ok, NULL);
  if (!ok) {
    log_fn(LOG_WARN, "Error parsing expected bandwidth");
    goto err;
  }

  n_bytes_read_in_interval = n_read;
  n_bytes_written_in_interval = n_written;
  n_seconds_active_in_interval = n_seconds;
  interval_start_time = t1;
  expected_bandwidth_usage = expected_bw;

  return 0;
 err:
  SMARTLIST_FOREACH(elts, char *, cp, tor_free(cp));
  smartlist_free(elts);
  return -1;
}

/** Return true iff we have sent/received all the bytes we are willing
 * to send/receive this interval. */
static int
hibernate_hard_limit_reached(void)
{
  uint64_t hard_limit = get_options()->AccountingMax;
  if (!hard_limit)
    return 0;
  return n_bytes_read_in_interval >= hard_limit
    || n_bytes_written_in_interval >= hard_limit;
}

/** Return true iff we have sent/received almost all the bytes we are willing
 * to send/receive this interval. */
static int hibernate_soft_limit_reached(void)
{
  uint64_t soft_limit = (uint64_t) ((get_options()->AccountingMax) * .99);
  if (!soft_limit)
    return 0;
  return n_bytes_read_in_interval >= soft_limit
    || n_bytes_written_in_interval >= soft_limit;
}

/** Called when we get a SIGINT, or when bandwidth soft limit is
 * reached. Puts us into "loose hibernation": we don't accept new
 * connections, but we continue handling old ones. */
static void hibernate_begin(int new_state, time_t now) {
  connection_t *conn;

  if (hibernate_state == HIBERNATE_STATE_EXITING) {
    /* we've been called twice now. close immediately. */
    log(LOG_NOTICE,"Second sigint received; exiting now.");
    tor_cleanup();
    exit(0);
  }

  /* close listeners. leave control listener(s). */
  while ((conn = connection_get_by_type(CONN_TYPE_OR_LISTENER)) ||
         (conn = connection_get_by_type(CONN_TYPE_AP_LISTENER)) ||
         (conn = connection_get_by_type(CONN_TYPE_DIR_LISTENER))) {
    log_fn(LOG_INFO,"Closing listener type %d", conn->type);
    connection_mark_for_close(conn);
  }

  /* XXX kill intro point circs */
  /* XXX upload rendezvous service descriptors with no intro points */

  if (new_state == HIBERNATE_STATE_EXITING) {
    log(LOG_NOTICE,"Interrupt: will shut down in %d seconds. Interrupt again to exit now.", SHUTDOWN_WAIT_LENGTH);
    hibernate_end_time = time(NULL) + SHUTDOWN_WAIT_LENGTH;
  } else { /* soft limit reached */
    hibernate_end_time = interval_end_time;
  }

  hibernate_state = new_state;
  accounting_record_bandwidth_usage(now);
}

/** Called when we've been hibernating and our timeout is reached. */
static void
hibernate_end(int new_state) {

  tor_assert(hibernate_state == HIBERNATE_STATE_LOWBANDWIDTH ||
             hibernate_state == HIBERNATE_STATE_DORMANT);

  /* listeners will be relaunched in run_scheduled_events() in main.c */
  log_fn(LOG_NOTICE,"Hibernation period ended. Resuming normal activity.");

  hibernate_state = new_state;
  hibernate_end_time = 0; /* no longer hibernating */
}

/** A wrapper around hibernate_begin, for when we get SIGINT. */
void
hibernate_begin_shutdown(void) {
  hibernate_begin(HIBERNATE_STATE_EXITING, time(NULL));
}

/** Return true iff we are currently hibernating. */
int
we_are_hibernating(void) {
  return hibernate_state != HIBERNATE_STATE_LIVE;
}

/** If we aren't currently dormant, close all connections and become
 * dormant. */
static void
hibernate_go_dormant(time_t now) {
  connection_t *conn;

  if (hibernate_state == HIBERNATE_STATE_DORMANT)
    return;
  else if (hibernate_state == HIBERNATE_STATE_LOWBANDWIDTH)
    hibernate_state = HIBERNATE_STATE_DORMANT;
  else
    hibernate_begin(HIBERNATE_STATE_DORMANT, now);

  log_fn(LOG_NOTICE,"Going dormant. Blowing away remaining connections.");

  /* Close all OR/AP/exit conns. Leave dir conns because we still want
   * to be able to upload server descriptors so people know we're still
   * running, and download directories so we can detect if we're obsolete.
   * Leave control conns because we still want to be controllable.
   */
  while ((conn = connection_get_by_type(CONN_TYPE_OR)) ||
         (conn = connection_get_by_type(CONN_TYPE_AP)) ||
         (conn = connection_get_by_type(CONN_TYPE_EXIT))) {
    log_fn(LOG_INFO,"Closing conn type %d", conn->type);
    connection_mark_for_close(conn);
  }

  accounting_record_bandwidth_usage(now);
}

/** Called when hibernate_end_time has arrived. */
static void
hibernate_end_time_elapsed(time_t now)
{
  char buf[ISO_TIME_LEN+1];

  /* The interval has ended, or it is wakeup time.  Find out which. */
  accounting_run_housekeeping(now);
  if (interval_wakeup_time <= now) {
    /* The interval hasn't changed, but interval_wakeup_time has passed.
     * It's time to wake up and start being a server. */
    hibernate_end(HIBERNATE_STATE_LIVE);
    return;
  } else {
    /* The interval has changed, and it isn't time to wake up yet. */
    hibernate_end_time = interval_wakeup_time;
    format_iso_time(buf,interval_wakeup_time);
    if (hibernate_state != HIBERNATE_STATE_DORMANT) {
      /* We weren't sleeping before; we should sleep now. */
      log_fn(LOG_NOTICE, "Accounting period ended. Commencing hibernation until %s GMT",buf);
      hibernate_go_dormant(now);
    } else {
      log_fn(LOG_NOTICE, "Accounting period ended. This period, we will hibernate until %s GMT",buf);
    }
  }
}

/** The big function. Consider our environment and decide if it's time
 * to start/stop hibernating.
 */
void consider_hibernation(time_t now) {
  int accounting_enabled = get_options()->AccountingMax != 0;
  char buf[ISO_TIME_LEN+1];

  /* If we're in 'exiting' mode, then we just shut down after the interval
   * elapses. */
  if (hibernate_state == HIBERNATE_STATE_EXITING) {
    tor_assert(hibernate_end_time);
    if (hibernate_end_time <= now) {
      log(LOG_NOTICE,"Clean shutdown finished. Exiting.");
      tor_cleanup();
      exit(0);
    }
    return; /* if exiting soon, don't worry about bandwidth limits */
  }

  if (hibernate_state == HIBERNATE_STATE_DORMANT) {
    /* We've been hibernating because of bandwidth accounting. */
    tor_assert(hibernate_end_time);
    if (hibernate_end_time > now && accounting_enabled) {
      /* If we're hibernating, don't wake up until it's time, regardless of
       * whether we're in a new interval. */
      return ;
    } else {
      hibernate_end_time_elapsed(now);
    }
  }

  /* Else, we aren't hibernating. See if it's time to start hibernating, or to
   * go dormant. */
  if (hibernate_state == HIBERNATE_STATE_LIVE) {
    if (hibernate_soft_limit_reached()) {
      log_fn(LOG_NOTICE,"Bandwidth soft limit reached; commencing hibernation.");
      hibernate_begin(HIBERNATE_STATE_LOWBANDWIDTH, now);
    } else if (accounting_enabled && now < interval_wakeup_time) {
      format_iso_time(buf,interval_wakeup_time);
      log_fn(LOG_NOTICE, "Commencing hibernation. We will wake up at %s GMT",buf);
      hibernate_go_dormant(now);
    }
  }

  if (hibernate_state == HIBERNATE_STATE_LOWBANDWIDTH) {
    if (!accounting_enabled) {
      hibernate_end_time_elapsed(now);
    } else if (hibernate_hard_limit_reached()) {
      hibernate_go_dormant(now);
    } else if (hibernate_end_time <= now) {
      /* The hibernation period ended while we were still in lowbandwidth.*/
      hibernate_end_time_elapsed(now);
    }
  }
}