Adding upstream version 4.5.upstream/4.5

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 866 insertions, 0 deletions

diff --git a/sched.c b/sched.c
new file mode 100644
index 0000000..676866e
--- /dev/null
+++ b/sched.c
@@ -0,0 +1,866 @@
+/*
+  chronyd/chronyc - Programs for keeping computer clocks accurate.
+
+ **********************************************************************
+ * Copyright (C) Richard P. Curnow  1997-2003
+ * Copyright (C) Miroslav Lichvar  2011, 2013-2016
+ * 
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of version 2 of the GNU General Public License as
+ * published by the Free Software Foundation.
+ * 
+ * This program 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 this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+ * 
+ **********************************************************************
+
+  =======================================================================
+
+  This file contains the scheduling loop and the timeout queue.
+
+  */
+
+#include "config.h"
+
+#include "sysincl.h"
+
+#include "array.h"
+#include "sched.h"
+#include "memory.h"
+#include "util.h"
+#include "local.h"
+#include "logging.h"
+
+/* ================================================== */
+
+/* Flag indicating that we are initialised */
+static int initialised = 0;
+
+/* ================================================== */
+
+/* One more than the highest file descriptor that is registered */
+static unsigned int one_highest_fd;
+
+#ifndef FD_SETSIZE
+/* If FD_SETSIZE is not defined, assume that fd_set is implemented
+   as a fixed size array of bits, possibly embedded inside a record */
+#define FD_SETSIZE (sizeof(fd_set) * 8)
+#endif
+
+typedef struct {
+  SCH_FileHandler       handler;
+  SCH_ArbitraryArgument arg;
+  int                   events;
+} FileHandlerEntry;
+
+static ARR_Instance file_handlers;
+
+/* Timestamp when last select() returned */
+static struct timespec last_select_ts, last_select_ts_raw;
+static double last_select_ts_err;
+
+#define TS_MONO_PRECISION_NS 10000000U
+
+/* Monotonic low-precision timestamp measuring interval since the start */
+static double last_select_ts_mono;
+static uint32_t last_select_ts_mono_ns;
+
+/* ================================================== */
+
+/* Variables to handler the timer queue */
+
+typedef struct _TimerQueueEntry
+{
+  struct _TimerQueueEntry *next; /* Forward and back links in the list */
+  struct _TimerQueueEntry *prev;
+  struct timespec ts;           /* Local system time at which the
+                                   timeout is to expire.  Clearly this
+                                   must be in terms of what the
+                                   operating system thinks of as
+                                   system time, because it will be an
+                                   argument to select().  Therefore,
+                                   any fudges etc that our local time
+                                   driver module would apply to time
+                                   that we pass to clients etc doesn't
+                                   apply to this. */
+  SCH_TimeoutID id;             /* ID to allow client to delete
+                                   timeout */
+  SCH_TimeoutClass class;       /* The class that the epoch is in */
+  SCH_TimeoutHandler handler;   /* The handler routine to use */
+  SCH_ArbitraryArgument arg;    /* The argument to pass to the handler */
+
+} TimerQueueEntry;
+
+/* The timer queue.  We only use the next and prev entries of this
+   record, these chain to the real entries. */
+static TimerQueueEntry timer_queue;
+static unsigned long n_timer_queue_entries;
+static SCH_TimeoutID next_tqe_id;
+
+/* Pointer to head of free list */
+static TimerQueueEntry *tqe_free_list;
+
+/* Array of all allocated tqe blocks to be freed in finalisation */
+static ARR_Instance tqe_blocks;
+
+/* Timestamp when was last timeout dispatched for each class */
+static struct timespec last_class_dispatch[SCH_NumberOfClasses];
+
+/* ================================================== */
+
+/* Flag terminating the main loop, which can be set from a signal handler */
+static volatile int need_to_exit;
+
+/* ================================================== */
+
+static void
+handle_slew(struct timespec *raw,
+            struct timespec *cooked,
+            double dfreq,
+            double doffset,
+            LCL_ChangeType change_type,
+            void *anything);
+
+/* ================================================== */
+
+void
+SCH_Initialise(void)
+{
+  file_handlers = ARR_CreateInstance(sizeof (FileHandlerEntry));
+
+  n_timer_queue_entries = 0;
+  next_tqe_id = 0;
+  tqe_free_list = NULL;
+  tqe_blocks = ARR_CreateInstance(sizeof (TimerQueueEntry *));
+
+  timer_queue.next = &timer_queue;
+  timer_queue.prev = &timer_queue;
+
+  need_to_exit = 0;
+
+  LCL_AddParameterChangeHandler(handle_slew, NULL);
+
+  LCL_ReadRawTime(&last_select_ts_raw);
+  last_select_ts = last_select_ts_raw;
+  last_select_ts_mono = 0.0;
+  last_select_ts_mono_ns = 0;
+
+  initialised = 1;
+}
+
+
+/* ================================================== */
+
+void
+SCH_Finalise(void) {
+  unsigned int i;
+
+  ARR_DestroyInstance(file_handlers);
+
+  timer_queue.next = &timer_queue;
+  timer_queue.prev = &timer_queue;
+  for (i = 0; i < ARR_GetSize(tqe_blocks); i++)
+    Free(*(TimerQueueEntry **)ARR_GetElement(tqe_blocks, i));
+  ARR_DestroyInstance(tqe_blocks);
+
+  LCL_RemoveParameterChangeHandler(handle_slew, NULL);
+
+  initialised = 0;
+}
+
+/* ================================================== */
+
+void
+SCH_AddFileHandler
+(int fd, int events, SCH_FileHandler handler, SCH_ArbitraryArgument arg)
+{
+  FileHandlerEntry *ptr;
+
+  assert(initialised);
+  assert(events);
+  assert(fd >= 0);
+  
+  if (fd >= FD_SETSIZE)
+    LOG_FATAL("Too many file descriptors");
+
+  /* Resize the array if the descriptor is highest so far */
+  while (ARR_GetSize(file_handlers) <= fd) {
+    ptr = ARR_GetNewElement(file_handlers);
+    ptr->handler = NULL;
+    ptr->arg = NULL;
+    ptr->events = 0;
+  }
+
+  ptr = ARR_GetElement(file_handlers, fd);
+
+  /* Don't want to allow the same fd to register a handler more than
+     once without deleting a previous association - this suggests
+     a bug somewhere else in the program. */
+  assert(!ptr->handler);
+
+  ptr->handler = handler;
+  ptr->arg = arg;
+  ptr->events = events;
+
+  if (one_highest_fd < fd + 1)
+    one_highest_fd = fd + 1;
+}
+
+
+/* ================================================== */
+
+void
+SCH_RemoveFileHandler(int fd)
+{
+  FileHandlerEntry *ptr;
+
+  assert(initialised);
+
+  ptr = ARR_GetElement(file_handlers, fd);
+
+  /* Check that a handler was registered for the fd in question */
+  assert(ptr->handler);
+
+  ptr->handler = NULL;
+  ptr->arg = NULL;
+  ptr->events = 0;
+
+  /* Find new highest file descriptor */
+  while (one_highest_fd > 0) {
+    ptr = ARR_GetElement(file_handlers, one_highest_fd - 1);
+    if (ptr->handler)
+      break;
+    one_highest_fd--;
+  }
+}
+
+/* ================================================== */
+
+void
+SCH_SetFileHandlerEvent(int fd, int event, int enable)
+{
+  FileHandlerEntry *ptr;
+
+  ptr = ARR_GetElement(file_handlers, fd);
+
+  if (enable)
+    ptr->events |= event;
+  else
+    ptr->events &= ~event;
+}
+
+/* ================================================== */
+
+void
+SCH_GetLastEventTime(struct timespec *cooked, double *err, struct timespec *raw)
+{
+  if (cooked) {
+    *cooked = last_select_ts;
+    if (err)
+      *err = last_select_ts_err;
+  }
+  if (raw)
+    *raw = last_select_ts_raw;
+}
+
+/* ================================================== */
+
+double
+SCH_GetLastEventMonoTime(void)
+{
+  return last_select_ts_mono;
+}
+
+/* ================================================== */
+
+#define TQE_ALLOC_QUANTUM 32
+
+static TimerQueueEntry *
+allocate_tqe(void)
+{
+  TimerQueueEntry *new_block;
+  TimerQueueEntry *result;
+  int i;
+  if (tqe_free_list == NULL) {
+    new_block = MallocArray(TimerQueueEntry, TQE_ALLOC_QUANTUM);
+    for (i=1; i<TQE_ALLOC_QUANTUM; i++) {
+      new_block[i].next = &(new_block[i-1]);
+    }
+    new_block[0].next = NULL;
+    tqe_free_list = &(new_block[TQE_ALLOC_QUANTUM - 1]);
+    ARR_AppendElement(tqe_blocks, &new_block);
+  }
+
+  result = tqe_free_list;
+  tqe_free_list = tqe_free_list->next;
+  return result;
+}
+
+/* ================================================== */
+
+static void
+release_tqe(TimerQueueEntry *node)
+{
+  node->next = tqe_free_list;
+  tqe_free_list = node;
+}
+
+/* ================================================== */
+
+static SCH_TimeoutID
+get_new_tqe_id(void)
+{
+  TimerQueueEntry *ptr;
+
+try_again:
+  next_tqe_id++;
+  if (!next_tqe_id)
+    goto try_again;
+
+  /* Make sure the ID isn't already used */
+  for (ptr = timer_queue.next; ptr != &timer_queue; ptr = ptr->next)
+    if (ptr->id == next_tqe_id)
+      goto try_again;
+
+  return next_tqe_id;
+}
+
+/* ================================================== */
+
+SCH_TimeoutID
+SCH_AddTimeout(struct timespec *ts, SCH_TimeoutHandler handler, SCH_ArbitraryArgument arg)
+{
+  TimerQueueEntry *new_tqe;
+  TimerQueueEntry *ptr;
+
+  assert(initialised);
+
+  new_tqe = allocate_tqe();
+
+  new_tqe->id = get_new_tqe_id();
+  new_tqe->handler = handler;
+  new_tqe->arg = arg;
+  new_tqe->ts = *ts;
+  new_tqe->class = SCH_ReservedTimeoutValue;
+
+  /* Now work out where to insert the new entry in the list */
+  for (ptr = timer_queue.next; ptr != &timer_queue; ptr = ptr->next) {
+    if (UTI_CompareTimespecs(&new_tqe->ts, &ptr->ts) == -1) {
+      /* If the new entry comes before the current pointer location in
+         the list, we want to insert the new entry just before ptr. */
+      break;
+    }
+  }
+
+  /* At this stage, we want to insert the new entry immediately before
+     the entry identified by 'ptr' */
+
+  new_tqe->next = ptr;
+  new_tqe->prev = ptr->prev;
+  ptr->prev->next = new_tqe;
+  ptr->prev = new_tqe;
+
+  n_timer_queue_entries++;
+
+  return new_tqe->id;
+}
+
+/* ================================================== */
+/* This queues a timeout to elapse at a given delta time relative to
+   the current (raw) time */
+
+SCH_TimeoutID
+SCH_AddTimeoutByDelay(double delay, SCH_TimeoutHandler handler, SCH_ArbitraryArgument arg)
+{
+  struct timespec now, then;
+
+  assert(initialised);
+  assert(delay >= 0.0);
+
+  LCL_ReadRawTime(&now);
+  UTI_AddDoubleToTimespec(&now, delay, &then);
+  if (UTI_CompareTimespecs(&now, &then) > 0) {
+    LOG_FATAL("Timeout overflow");
+  }
+
+  return SCH_AddTimeout(&then, handler, arg);
+
+}
+
+/* ================================================== */
+
+SCH_TimeoutID
+SCH_AddTimeoutInClass(double min_delay, double separation, double randomness,
+                      SCH_TimeoutClass class,
+                      SCH_TimeoutHandler handler, SCH_ArbitraryArgument arg)
+{
+  TimerQueueEntry *new_tqe;
+  TimerQueueEntry *ptr;
+  struct timespec now;
+  double diff, r;
+  double new_min_delay;
+
+  assert(initialised);
+  assert(min_delay >= 0.0);
+  assert(class < SCH_NumberOfClasses);
+
+  if (randomness > 0.0) {
+    uint32_t rnd;
+
+    UTI_GetRandomBytes(&rnd, sizeof (rnd));
+    r = rnd * (randomness / (uint32_t)-1) + 1.0;
+    min_delay *= r;
+    separation *= r;
+  }
+  
+  LCL_ReadRawTime(&now);
+  new_min_delay = min_delay;
+
+  /* Check the separation from the last dispatched timeout */
+  diff = UTI_DiffTimespecsToDouble(&now, &last_class_dispatch[class]);
+  if (diff < separation && diff >= 0.0 && diff + new_min_delay < separation) {
+    new_min_delay = separation - diff;
+  }
+
+  /* Scan through list for entries in the same class and increase min_delay
+     if necessary to keep at least the separation away */
+  for (ptr = timer_queue.next; ptr != &timer_queue; ptr = ptr->next) {
+    if (ptr->class == class) {
+      diff = UTI_DiffTimespecsToDouble(&ptr->ts, &now);
+      if (new_min_delay > diff) {
+        if (new_min_delay - diff < separation) {
+          new_min_delay = diff + separation;
+        }
+      } else {
+        if (diff - new_min_delay < separation) {
+          new_min_delay = diff + separation;
+        }
+      }
+    }
+  }
+
+  for (ptr = timer_queue.next; ptr != &timer_queue; ptr = ptr->next) {
+    diff = UTI_DiffTimespecsToDouble(&ptr->ts, &now);
+    if (diff > new_min_delay) {
+      break;
+    }
+  }
+
+  /* We have located the insertion point */
+  new_tqe = allocate_tqe();
+
+  new_tqe->id = get_new_tqe_id();
+  new_tqe->handler = handler;
+  new_tqe->arg = arg;
+  UTI_AddDoubleToTimespec(&now, new_min_delay, &new_tqe->ts);
+  new_tqe->class = class;
+
+  new_tqe->next = ptr;
+  new_tqe->prev = ptr->prev;
+  ptr->prev->next = new_tqe;
+  ptr->prev = new_tqe;
+  n_timer_queue_entries++;
+
+  return new_tqe->id;
+}
+
+/* ================================================== */
+
+void
+SCH_RemoveTimeout(SCH_TimeoutID id)
+{
+  TimerQueueEntry *ptr;
+
+  assert(initialised);
+
+  if (!id)
+    return;
+
+  for (ptr = timer_queue.next; ptr != &timer_queue; ptr = ptr->next) {
+
+    if (ptr->id == id) {
+      /* Found the required entry */
+      
+      /* Unlink from the queue */
+      ptr->next->prev = ptr->prev;
+      ptr->prev->next = ptr->next;
+      
+      /* Decrement entry count */
+      --n_timer_queue_entries;
+      
+      /* Release memory back to the operating system */
+      release_tqe(ptr);
+
+      return;
+    }
+  }
+
+  /* Catch calls with invalid non-zero ID */
+  assert(0);
+}
+
+/* ================================================== */
+/* Try to dispatch any timeouts that have already gone by, and
+   keep going until all are done.  (The earlier ones may take so
+   long to do that the later ones come around by the time they are
+   completed). */
+
+static void
+dispatch_timeouts(struct timespec *now) {
+  unsigned long n_done, n_entries_on_start;
+  TimerQueueEntry *ptr;
+  SCH_TimeoutHandler handler;
+  SCH_ArbitraryArgument arg;
+
+  n_entries_on_start = n_timer_queue_entries;
+  n_done = 0;
+
+  do {
+    LCL_ReadRawTime(now);
+
+    if (!(n_timer_queue_entries > 0 &&
+          UTI_CompareTimespecs(now, &timer_queue.next->ts) >= 0)) {
+      break;
+    }
+
+    ptr = timer_queue.next;
+
+    last_class_dispatch[ptr->class] = *now;
+
+    handler = ptr->handler;
+    arg = ptr->arg;
+
+    SCH_RemoveTimeout(ptr->id);
+
+    /* Dispatch the handler */
+    (handler)(arg);
+
+    /* Increment count of timeouts handled */
+    ++n_done;
+
+    /* If the number of dispatched timeouts is significantly larger than the
+       length of the queue on start and now, assume there is a bug causing
+       an infinite loop by constantly adding a timeout with a zero or negative
+       delay.  Check the actual rate of timeouts to avoid false positives in
+       case the execution slowed down so much (e.g. due to memory thrashing)
+       that it repeatedly takes more time to handle the timeout than is its
+       delay.  This is a safety mechanism intended to stop a full-speed flood
+       of NTP requests due to a bug in the NTP polling. */
+
+    if (n_done > 20 &&
+        n_done > 4 * MAX(n_timer_queue_entries, n_entries_on_start) &&
+        fabs(UTI_DiffTimespecsToDouble(now, &last_select_ts_raw)) / n_done < 0.01)
+      LOG_FATAL("Possible infinite loop in scheduling");
+
+  } while (!need_to_exit);
+}
+
+/* ================================================== */
+
+/* nfd is the number of bits set in all fd_sets */
+
+static void
+dispatch_filehandlers(int nfd, fd_set *read_fds, fd_set *write_fds, fd_set *except_fds)
+{
+  FileHandlerEntry *ptr;
+  int fd;
+  
+  for (fd = 0; nfd && fd < one_highest_fd; fd++) {
+    if (except_fds && FD_ISSET(fd, except_fds)) {
+      /* This descriptor has an exception, dispatch its handler */
+      ptr = (FileHandlerEntry *)ARR_GetElement(file_handlers, fd);
+      if (ptr->handler)
+        (ptr->handler)(fd, SCH_FILE_EXCEPTION, ptr->arg);
+      nfd--;
+
+      /* Don't try to read from it now */
+      if (read_fds && FD_ISSET(fd, read_fds)) {
+        FD_CLR(fd, read_fds);
+        nfd--;
+      }
+    }
+
+    if (read_fds && FD_ISSET(fd, read_fds)) {
+      /* This descriptor can be read from, dispatch its handler */
+      ptr = (FileHandlerEntry *)ARR_GetElement(file_handlers, fd);
+      if (ptr->handler)
+        (ptr->handler)(fd, SCH_FILE_INPUT, ptr->arg);
+      nfd--;
+    }
+
+    if (write_fds && FD_ISSET(fd, write_fds)) {
+      /* This descriptor can be written to, dispatch its handler */
+      ptr = (FileHandlerEntry *)ARR_GetElement(file_handlers, fd);
+      if (ptr->handler)
+        (ptr->handler)(fd, SCH_FILE_OUTPUT, ptr->arg);
+      nfd--;
+    }
+  }
+}
+
+/* ================================================== */
+
+static void
+handle_slew(struct timespec *raw,
+            struct timespec *cooked,
+            double dfreq,
+            double doffset,
+            LCL_ChangeType change_type,
+            void *anything)
+{
+  TimerQueueEntry *ptr;
+  double delta;
+  int i;
+
+  if (change_type != LCL_ChangeAdjust) {
+    /* Make sure this handler is invoked first in order to not shift new timers
+       added from other handlers */
+    assert(LCL_IsFirstParameterChangeHandler(handle_slew));
+
+    /* If a step change occurs, just shift all raw time stamps by the offset */
+    
+    for (ptr = timer_queue.next; ptr != &timer_queue; ptr = ptr->next) {
+      UTI_AddDoubleToTimespec(&ptr->ts, -doffset, &ptr->ts);
+    }
+
+    for (i = 0; i < SCH_NumberOfClasses; i++) {
+      UTI_AddDoubleToTimespec(&last_class_dispatch[i], -doffset, &last_class_dispatch[i]);
+    }
+
+    UTI_AddDoubleToTimespec(&last_select_ts_raw, -doffset, &last_select_ts_raw);
+  }
+
+  UTI_AdjustTimespec(&last_select_ts, cooked, &last_select_ts, &delta, dfreq, doffset);
+}
+
+/* ================================================== */
+
+static void
+fill_fd_sets(fd_set **read_fds, fd_set **write_fds, fd_set **except_fds)
+{
+  FileHandlerEntry *handlers;
+  fd_set *rd, *wr, *ex;
+  int i, n, events;
+
+  n = ARR_GetSize(file_handlers);
+  handlers = ARR_GetElements(file_handlers);
+  rd = wr = ex = NULL;
+
+  for (i = 0; i < n; i++) {
+    events = handlers[i].events;
+
+    if (!events)
+      continue;
+
+    if (events & SCH_FILE_INPUT) {
+      if (!rd) {
+        rd = *read_fds;
+        FD_ZERO(rd);
+      }
+      FD_SET(i, rd);
+    }
+
+    if (events & SCH_FILE_OUTPUT) {
+      if (!wr) {
+        wr = *write_fds;
+        FD_ZERO(wr);
+      }
+      FD_SET(i, wr);
+    }
+
+    if (events & SCH_FILE_EXCEPTION) {
+      if (!ex) {
+        ex = *except_fds;
+        FD_ZERO(ex);
+      }
+      FD_SET(i, ex);
+    }
+  }
+
+  if (!rd)
+    *read_fds = NULL;
+  if (!wr)
+    *write_fds = NULL;
+  if (!ex)
+    *except_fds = NULL;
+}
+
+/* ================================================== */
+
+#define JUMP_DETECT_THRESHOLD 10
+
+static int
+check_current_time(struct timespec *prev_raw, struct timespec *raw, int timeout,
+                   struct timeval *orig_select_tv,
+                   struct timeval *rem_select_tv)
+{
+  struct timespec elapsed_min, elapsed_max, orig_select_ts, rem_select_ts;
+  double step, elapsed;
+
+  UTI_TimevalToTimespec(orig_select_tv, &orig_select_ts);
+
+  /* Get an estimate of the time spent waiting in the select() call. On some
+     systems (e.g. Linux) the timeout timeval is modified to return the
+     remaining time, use that information. */
+  if (timeout) {
+    elapsed_max = elapsed_min = orig_select_ts;
+  } else if (rem_select_tv && rem_select_tv->tv_sec >= 0 &&
+             rem_select_tv->tv_sec <= orig_select_tv->tv_sec &&
+             (rem_select_tv->tv_sec != orig_select_tv->tv_sec ||
+              rem_select_tv->tv_usec != orig_select_tv->tv_usec)) {
+    UTI_TimevalToTimespec(rem_select_tv, &rem_select_ts);
+    UTI_DiffTimespecs(&elapsed_min, &orig_select_ts, &rem_select_ts);
+    elapsed_max = elapsed_min;
+  } else {
+    if (rem_select_tv)
+      elapsed_max = orig_select_ts;
+    else
+      UTI_DiffTimespecs(&elapsed_max, raw, prev_raw);
+    UTI_ZeroTimespec(&elapsed_min);
+  }
+
+  if (last_select_ts_raw.tv_sec + elapsed_min.tv_sec >
+      raw->tv_sec + JUMP_DETECT_THRESHOLD) {
+    LOG(LOGS_WARN, "Backward time jump detected!");
+  } else if (prev_raw->tv_sec + elapsed_max.tv_sec + JUMP_DETECT_THRESHOLD <
+             raw->tv_sec) {
+    LOG(LOGS_WARN, "Forward time jump detected!");
+  } else {
+    return 1;
+  }
+
+  step = UTI_DiffTimespecsToDouble(&last_select_ts_raw, raw);
+  elapsed = UTI_TimespecToDouble(&elapsed_min);
+  step += elapsed;
+
+  /* Cooked time may no longer be valid after dispatching the handlers */
+  LCL_NotifyExternalTimeStep(raw, raw, step, fabs(step));
+
+  return 0;
+}
+
+/* ================================================== */
+
+static void
+update_monotonic_time(struct timespec *now, struct timespec *before)
+{
+  struct timespec diff;
+
+  /* Avoid frequent floating-point operations and handle small
+     increments to a large value */
+
+  UTI_DiffTimespecs(&diff, now, before);
+  if (diff.tv_sec == 0) {
+    last_select_ts_mono_ns += diff.tv_nsec;
+  } else {
+    last_select_ts_mono += fabs(UTI_TimespecToDouble(&diff) +
+                                last_select_ts_mono_ns / 1.0e9);
+    last_select_ts_mono_ns = 0;
+  }
+
+  if (last_select_ts_mono_ns > TS_MONO_PRECISION_NS) {
+    last_select_ts_mono += last_select_ts_mono_ns / 1.0e9;
+    last_select_ts_mono_ns = 0;
+  }
+}
+
+/* ================================================== */
+
+void
+SCH_MainLoop(void)
+{
+  fd_set read_fds, write_fds, except_fds;
+  fd_set *p_read_fds, *p_write_fds, *p_except_fds;
+  int status, errsv;
+  struct timeval tv, saved_tv, *ptv;
+  struct timespec ts, now, saved_now, cooked;
+  double err;
+
+  assert(initialised);
+
+  while (!need_to_exit) {
+    /* Dispatch timeouts and fill now with current raw time */
+    dispatch_timeouts(&now);
+    saved_now = now;
+    
+    /* The timeout handlers may request quit */
+    if (need_to_exit)
+      break;
+
+    /* Check whether there is a timeout and set it up */
+    if (n_timer_queue_entries > 0) {
+      UTI_DiffTimespecs(&ts, &timer_queue.next->ts, &now);
+      assert(ts.tv_sec > 0 || ts.tv_nsec > 0);
+
+      UTI_TimespecToTimeval(&ts, &tv);
+      ptv = &tv;
+      saved_tv = tv;
+    } else {
+      ptv = NULL;
+      saved_tv.tv_sec = saved_tv.tv_usec = 0;
+    }
+
+    p_read_fds = &read_fds;
+    p_write_fds = &write_fds;
+    p_except_fds = &except_fds;
+    fill_fd_sets(&p_read_fds, &p_write_fds, &p_except_fds);
+
+    /* if there are no file descriptors being waited on and no
+       timeout set, this is clearly ridiculous, so stop the run */
+    if (!ptv && !p_read_fds && !p_write_fds)
+      LOG_FATAL("Nothing to do");
+
+    status = select(one_highest_fd, p_read_fds, p_write_fds, p_except_fds, ptv);
+    errsv = errno;
+
+    LCL_ReadRawTime(&now);
+    LCL_CookTime(&now, &cooked, &err);
+
+    update_monotonic_time(&now, &last_select_ts_raw);
+
+    /* Check if the time didn't jump unexpectedly */
+    if (!check_current_time(&saved_now, &now, status == 0, &saved_tv, ptv)) {
+      /* Cook the time again after handling the step */
+      LCL_CookTime(&now, &cooked, &err);
+    }
+
+    last_select_ts_raw = now;
+    last_select_ts = cooked;
+    last_select_ts_err = err;
+
+    if (status < 0) {
+      if (!need_to_exit && errsv != EINTR) {
+        LOG_FATAL("select() failed : %s", strerror(errsv));
+      }
+    } else if (status > 0) {
+      /* A file descriptor is ready for input or output */
+      dispatch_filehandlers(status, p_read_fds, p_write_fds, p_except_fds);
+    } else {
+      /* No descriptors readable, timeout must have elapsed.
+       Therefore, tv must be non-null */
+      assert(ptv);
+
+      /* There's nothing to do here, since the timeouts
+         will be dispatched at the top of the next loop
+         cycle */
+
+    }
+  }         
+}
+
+/* ================================================== */
+
+void
+SCH_QuitProgram(void)
+{
+  need_to_exit = 1;
+}
+
+/* ================================================== */
+