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chrony/sched.c
Miroslav Lichvar ba875fc04a sched: allocate file handlers dynamically
2014-09-25 10:58:57 +02:00

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/*
chronyd/chronyc - Programs for keeping computer clocks accurate.
**********************************************************************
* Copyright (C) Richard P. Curnow 1997-2003
* Copyright (C) Miroslav Lichvar 2011, 2013-2014
*
* 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;
/* ================================================== */
/* Variables to handle the capability to dispatch on particular file
handles becoming readable */
/* Each bit set in this fd set corresponds to a read descriptor that
we are watching and with which we have a handler associated in the
file_handlers array */
static fd_set read_fds;
/* This is the number of bits that we have set in read_fds */
static unsigned int n_read_fds;
/* 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;
} FileHandlerEntry;
static ARR_Instance file_handlers;
/* Timestamp when last select() returned */
static struct timeval last_select_ts, last_select_ts_raw;
static double last_select_ts_err;
/* ================================================== */
/* Variables to handler the timer queue */
typedef struct _TimerQueueEntry
{
struct _TimerQueueEntry *next; /* Forward and back links in the list */
struct _TimerQueueEntry *prev;
struct timeval tv; /* 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 = NULL;
/* Timestamp when was last timeout dispatched for each class */
static struct timeval last_class_dispatch[SCH_NumberOfClasses];
/* ================================================== */
static int need_to_exit;
/* ================================================== */
static void
handle_slew(struct timeval *raw,
struct timeval *cooked,
double dfreq,
double doffset,
LCL_ChangeType change_type,
void *anything);
/* ================================================== */
void
SCH_Initialise(void)
{
FD_ZERO(&read_fds);
n_read_fds = 0;
file_handlers = ARR_CreateInstance(sizeof (FileHandlerEntry));
n_timer_queue_entries = 0;
next_tqe_id = 0;
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;
srandom(last_select_ts.tv_sec << 16 ^ last_select_ts.tv_usec);
initialised = 1;
}
/* ================================================== */
void
SCH_Finalise(void) {
ARR_DestroyInstance(file_handlers);
initialised = 0;
}
/* ================================================== */
void
SCH_AddInputFileHandler
(int fd, SCH_FileHandler handler, SCH_ArbitraryArgument arg)
{
FileHandlerEntry *ptr;
assert(initialised);
if (fd >= FD_SETSIZE)
LOG_FATAL(LOGF_Scheduler, "Too many file descriptors");
/* 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(!FD_ISSET(fd, &read_fds));
++n_read_fds;
if (ARR_GetSize(file_handlers) < fd + 1)
ARR_SetSize(file_handlers, fd + 1);
ptr = (FileHandlerEntry *)ARR_GetElement(file_handlers, fd);
ptr->handler = handler;
ptr->arg = arg;
FD_SET(fd, &read_fds);
if ((fd + 1) > one_highest_fd) {
one_highest_fd = fd + 1;
}
}
/* ================================================== */
void
SCH_RemoveInputFileHandler(int fd)
{
int fds_left, fd_to_check;
assert(initialised);
/* Check that a handler was registered for the fd in question */
assert(FD_ISSET(fd, &read_fds));
--n_read_fds;
FD_CLR(fd, &read_fds);
/* Find new highest file descriptor */
fds_left = n_read_fds;
fd_to_check = 0;
while (fds_left > 0) {
if (FD_ISSET(fd_to_check, &read_fds)) {
--fds_left;
}
++fd_to_check;
}
one_highest_fd = fd_to_check;
}
/* ================================================== */
void
SCH_GetLastEventTime(struct timeval *cooked, double *err, struct timeval *raw)
{
if (cooked) {
*cooked = last_select_ts;
if (err)
*err = last_select_ts_err;
}
if (raw)
*raw = last_select_ts_raw;
}
/* ================================================== */
#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]);
}
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;
}
/* ================================================== */
SCH_TimeoutID
SCH_AddTimeout(struct timeval *tv, SCH_TimeoutHandler handler, SCH_ArbitraryArgument arg)
{
TimerQueueEntry *new_tqe;
TimerQueueEntry *ptr;
assert(initialised);
new_tqe = allocate_tqe();
new_tqe->id = next_tqe_id++;
new_tqe->handler = handler;
new_tqe->arg = arg;
new_tqe->tv = *tv;
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_CompareTimevals(&new_tqe->tv, &ptr->tv) == -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 timeval now, then;
assert(initialised);
assert(delay >= 0.0);
LCL_ReadRawTime(&now);
UTI_AddDoubleToTimeval(&now, delay, &then);
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 timeval now;
double diff, r;
double new_min_delay;
assert(initialised);
assert(min_delay >= 0.0);
assert(class < SCH_NumberOfClasses);
if (randomness > 0.0) {
r = random() % 0xffff / (0xffff - 1.0) * randomness + 1.0;
min_delay *= r;
separation *= r;
}
LCL_ReadRawTime(&now);
new_min_delay = min_delay;
/* Check the separation from the last dispatched timeout */
UTI_DiffTimevalsToDouble(&diff, &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) {
UTI_DiffTimevalsToDouble(&diff, &ptr->tv, &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) {
UTI_DiffTimevalsToDouble(&diff, &ptr->tv, &now);
if (diff > new_min_delay) {
break;
}
}
/* We have located the insertion point */
new_tqe = allocate_tqe();
new_tqe->id = next_tqe_id++;
new_tqe->handler = handler;
new_tqe->arg = arg;
UTI_AddDoubleToTimeval(&now, new_min_delay, &new_tqe->tv);
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);
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);
break;
}
}
}
/* ================================================== */
/* 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 timeval *now) {
TimerQueueEntry *ptr;
SCH_TimeoutHandler handler;
SCH_ArbitraryArgument arg;
int n_done = 0, n_entries_on_start = n_timer_queue_entries;
while (1) {
LCL_ReadRawTime(now);
if (!(n_timer_queue_entries > 0 &&
UTI_CompareTimevals(now, &(timer_queue.next->tv)) >= 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 more timeouts were handled than there were in the timer queue on
start and there are now, assume some code is scheduling timeouts with
negative delays and abort. Make the actual limit higher in case the
machine is temporarily overloaded and dispatching the handlers takes
more time than was delay of a scheduled timeout. */
if (n_done > n_timer_queue_entries * 4 &&
n_done > n_entries_on_start * 4) {
LOG_FATAL(LOGF_Scheduler, "Possible infinite loop in scheduling");
}
}
}
/* ================================================== */
/* nfh is the number of bits set in fhs */
static void
dispatch_filehandlers(int nfh, fd_set *fhs)
{
FileHandlerEntry *ptr;
int fh = 0;
while (nfh > 0) {
if (FD_ISSET(fh, fhs)) {
/* This descriptor can be read from, dispatch its handler */
ptr = (FileHandlerEntry *)ARR_GetElement(file_handlers, fh);
(ptr->handler)(ptr->arg);
/* Decrement number of readable files still to find */
--nfh;
}
++fh;
}
}
/* ================================================== */
static void
handle_slew(struct timeval *raw,
struct timeval *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_AddDoubleToTimeval(&ptr->tv, -doffset, &ptr->tv);
}
for (i = 0; i < SCH_NumberOfClasses; i++) {
UTI_AddDoubleToTimeval(&last_class_dispatch[i], -doffset, &last_class_dispatch[i]);
}
UTI_AddDoubleToTimeval(&last_select_ts_raw, -doffset, &last_select_ts_raw);
}
UTI_AdjustTimeval(&last_select_ts, cooked, &last_select_ts, &delta, dfreq, doffset);
}
/* ================================================== */
#define JUMP_DETECT_THRESHOLD 10
static int
check_current_time(struct timeval *prev_raw, struct timeval *raw, int timeout,
struct timeval *orig_select_tv,
struct timeval *rem_select_tv)
{
struct timeval elapsed_min, elapsed_max;
double step, elapsed;
/* 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_tv;
} 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_DiffTimevals(&elapsed_min, orig_select_tv, rem_select_tv);
elapsed_max = elapsed_min;
} else {
if (rem_select_tv)
elapsed_max = *orig_select_tv;
else
UTI_DiffTimevals(&elapsed_max, raw, prev_raw);
elapsed_min.tv_sec = 0;
elapsed_min.tv_usec = 0;
}
if (last_select_ts_raw.tv_sec + elapsed_min.tv_sec >
raw->tv_sec + JUMP_DETECT_THRESHOLD) {
LOG(LOGS_WARN, LOGF_Scheduler, "Backward time jump detected!");
} else if (prev_raw->tv_sec + elapsed_max.tv_sec + JUMP_DETECT_THRESHOLD <
raw->tv_sec) {
LOG(LOGS_WARN, LOGF_Scheduler, "Forward time jump detected!");
} else {
return 1;
}
UTI_DiffTimevalsToDouble(&step, &last_select_ts_raw, raw);
UTI_TimevalToDouble(&elapsed_min, &elapsed);
step += elapsed;
/* Cooked time may no longer be valid after dispatching the handlers */
LCL_NotifyExternalTimeStep(raw, raw, step, fabs(step));
return 0;
}
/* ================================================== */
void
SCH_MainLoop(void)
{
fd_set rd;
int status, errsv;
struct timeval tv, saved_tv, *ptv;
struct timeval 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_DiffTimevals(&tv, &(timer_queue.next->tv), &now);
ptv = &tv;
assert(tv.tv_sec > 0 || tv.tv_usec > 0);
saved_tv = tv;
} else {
ptv = NULL;
/* This is needed to fix a compiler warning */
saved_tv.tv_sec = 0;
}
/* if there are no file descriptors being waited on and no
timeout set, this is clearly ridiculous, so stop the run */
if (!ptv && !n_read_fds) {
LOG_FATAL(LOGF_Scheduler, "Nothing to do");
}
/* Copy current set of read file descriptors */
memcpy((void *) &rd, (void *) &read_fds, sizeof(fd_set));
status = select(one_highest_fd, &rd, NULL, NULL, ptv);
errsv = errno;
LCL_ReadRawTime(&now);
LCL_CookTime(&now, &cooked, &err);
/* 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(LOGF_Scheduler, "select() failed : %s", strerror(errsv));
}
} else if (status > 0) {
/* A file descriptor is ready to read */
dispatch_filehandlers(status, &rd);
} 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)
{
assert(initialised);
need_to_exit = 1;
}
/* ================================================== */
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