深入探讨Cron任务调度系统的高效实现-优快云博客

cron_Paul_Vixie.zip

/* $OpenBSD: cron.c,v 1.39 2007/02/18 23:59:03 jmc Exp $ */
*/
/*
*
* Permission to use, copy, modify, and distribute this software for any
* purpose with or without fee is hereby granted, provided that the above
* copyright notice and this permission notice appear in all copies.
*
* THE SOFTWARE IS PROVIDED "AS IS" AND ISC DISCLAIMS ALL WARRANTIES
* WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
* MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL ISC BE LIABLE FOR
* ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
* WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
* ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT
* OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
*/
#if !defined(lint) && !defined(LINT)
static const char rcsid[] = "$OpenBSD: cron.c,v 1.39 2007/02/18 23:59:03 jmc Exp $";
#endif
#define MAIN_PROGRAM
#include "cron.h"
enum timejump { negative, small, medium, large };
static void usage(void),
run_reboot_jobs(cron_db *),
find_jobs(int, cron_db *, int, int),
set_time(int),
cron_sleep(int),
sigchld_handler(int),
sighup_handler(int),
sigchld_reaper(void),
quit(int),
parse_args(int c, char *v[]);
static volatile sig_atomic_t got_sighup, got_sigchld;
static int timeRunning, virtualTime, clockTime, cronSock;
static long GMToff;
static cron_db database;
static at_db at_database;
static double batch_maxload = BATCH_MAXLOAD;
static void
usage(void) {
#if DEBUGGING
const char **dflags;
#endif
fprintf(stderr, "usage: %s [-n] [-l load_avg] [-x [", ProgramName);
#if DEBUGGING
for (dflags = DebugFlagNames; *dflags; dflags++)
fprintf(stderr, "%s%s", *dflags, dflags[1] ? "," : "]");
#else
fprintf(stderr, "debugging flags (none supported in this build)]");
#endif
fprintf(stderr, "]\n");
exit(ERROR_EXIT);
}
int
main(int argc, char *argv[]) {
struct sigaction sact;
int fd;
ProgramName = argv[0];
setlocale(LC_ALL, "");
#if defined(BSD)
setlinebuf(stdout);
setlinebuf(stderr);
#endif
NoFork = 0;
parse_args(argc, argv);
bzero((char *)&sact, sizeof sact);
sigemptyset(&sact.sa_mask);
sact.sa_flags = 0;
#ifdef SA_RESTART
sact.sa_flags |= SA_RESTART;
#endif
sact.sa_handler = sigchld_handler;
(void) sigaction(SIGCHLD, &sact, NULL);
sact.sa_handler = sighup_handler;
(void) sigaction(SIGHUP, &sact, NULL);
sact.sa_handler = quit;
(void) sigaction(SIGINT, &sact, NULL);
(void) sigaction(SIGTERM, &sact, NULL);
sact.sa_handler = SIG_IGN;
(void) sigaction(SIGPIPE, &sact, NULL);
(void) sigaction(SIGUSR1, &sact, NULL); /* XXX */
acquire_daemonlock(0);
set_cron_uid();
set_cron_cwd();
if (putenv("PATH="_PATH_DEFPATH) 0) {
log_it("CRON", getpid(), "DEATH", "can't malloc");
exit(1);
}
/* if there are no debug flags turned on, fork as a daemon should.
*/
if (DebugFlags) {
#if DEBUGGING
(void) fprintf(stderr, "[%ld] cron started\n", (long)getpid());
#endif
} else if (NoFork == 0) {
switch (fork()) {
case -1:
log_it("CRON",getpid(),"DEATH","can't fork");
exit(0);
break;
case 0:
/* child process */
(void) setsid();
if ((fd = open(_PATH_DEVNULL, O_RDWR, 0)) >= 0) {
(void) dup2(fd, STDIN);
(void) dup2(fd, STDOUT);
(void) dup2(fd, STDERR);
if (fd != STDERR)
(void) close(fd);
}
log_it("CRON",getpid(),"STARTUP",CRON_VERSION);
break;
default:
/* parent process should just die */
_exit(0);
}
}
acquire_daemonlock(0);
cronSock = open_socket();
database.head = NULL;
database.tail = NULL;
database.mtime = (time_t) 0;
load_database(&database);
at_database.head = NULL;
at_database.tail = NULL;
at_database.mtime = (time_t) 0;
scan_atjobs(&at_database, NULL);
set_time(TRUE);
run_reboot_jobs(&database);
timeRunning = virtualTime = clockTime;
/*
* Too many clocks, not enough time (Al. Einstein)
* These clocks are in minutes since the epoch, adjusted for timezone.
* virtualTime: is the time it *would* be if we woke up
* promptly and nobody ever changed the clock. It is
* monotonically increasing... unless a timejump happens.
* At the top of the loop, all jobs for 'virtualTime' have run.
* timeRunning: is the time we last awakened.
* clockTime: is the time when set_time was last called.
*/
while (TRUE) {
int timeDiff;
enum timejump wakeupKind;
/* ... wait for the time (in minutes) to change ... */
do {
cron_sleep(timeRunning + 1);
set_time(FALSE);
} while (clockTime == timeRunning);
timeRunning = clockTime;
/*
* Calculate how the current time differs from our virtual
* clock. Classify the change into one of 4 cases.
*/
timeDiff = timeRunning - virtualTime;
/* shortcut for the most common case */
if (timeDiff == 1) {
virtualTime = timeRunning;
find_jobs(virtualTime, &database, TRUE, TRUE);
} else {
if (timeDiff > (3*MINUTE_COUNT) ||
timeDiff -(3*MINUTE_COUNT))
wakeupKind = large;
else if (timeDiff > 5)
wakeupKind = medium;
else if (timeDiff > 0)
wakeupKind = small;
else
wakeupKind = negative;
switch (wakeupKind) {
case small:
/*
* case 1: timeDiff is a small positive number
* (wokeup late) run jobs for each virtual
* minute until caught up.
*/
Debug(DSCH, ("[%ld], normal case %d minutes to go\n",
(long)getpid(), timeDiff))
do {
if (job_runqueue())
sleep(10);
virtualTime++;
find_jobs(virtualTime, &database,
TRUE, TRUE);
} while (virtualTime timeRunning);
break;
case medium:
/*
* case 2: timeDiff is a medium-sized positive
* number, for example because we went to DST
* run wildcard jobs once, then run any
* fixed-time jobs that would otherwise be
* skipped if we use up our minute (possible,
* if there are a lot of jobs to run) go
* around the loop again so that wildcard jobs
* have a chance to run, and we do our
* housekeeping.
*/
Debug(DSCH, ("[%ld], DST begins %d minutes to go\n",
(long)getpid(), timeDiff))
/* run wildcard jobs for current minute */
find_jobs(timeRunning, &database, TRUE, FALSE);
/* run fixed-time jobs for each minute missed */
do {
if (job_runqueue())
sleep(10);
virtualTime++;
find_jobs(virtualTime, &database,
FALSE, TRUE);
set_time(FALSE);
} while (virtualTime timeRunning &&
clockTime == timeRunning);
break;
case negative:
/*
* case 3: timeDiff is a small or medium-sized
* negative num, eg. because of DST ending.
* Just run the wildcard jobs. The fixed-time
* jobs probably have already run, and should
* not be repeated. Virtual time does not
* change until we are caught up.
*/
Debug(DSCH, ("[%ld], DST ends %d minutes to go\n",
(long)getpid(), timeDiff))
find_jobs(timeRunning, &database, TRUE, FALSE);
break;
default:
/*
* other: time has changed a *lot*,
* jump virtual time, and run everything
*/
Debug(DSCH, ("[%ld], clock jumped\n",
(long)getpid()))
virtualTime = timeRunning;
find_jobs(timeRunning, &database, TRUE, TRUE);
}
}
/* Jobs to be run (if any) are loaded; clear the queue. */
job_runqueue();
/* Run any jobs in the at queue. */
atrun(&at_database, batch_maxload,
timeRunning * SECONDS_PER_MINUTE - GMToff);
/* Check to see if we received a signal while running jobs. */
if (got_sighup) {
got_sighup = 0;
log_close();
}
if (got_sigchld) {
got_sigchld = 0;
sigchld_reaper();
}
load_database(&database);
scan_atjobs(&at_database, NULL);
}
}
static void
run_reboot_jobs(cron_db *db) {
user *u;
entry *e;
for (u = db->head; u != NULL; u = u->next) {
for (e = u->crontab; e != NULL; e = e->next) {
if (e->flags & WHEN_REBOOT)
job_add(e, u);
}
}
(void) job_runqueue();
}
static void
find_jobs(int vtime, cron_db *db, int doWild, int doNonWild) {
time_t virtualSecond = vtime * SECONDS_PER_MINUTE;
struct tm *tm = gmtime(&virtualSecond);
int minute, hour, dom, month, dow;
user *u;
entry *e;
/* make 0-based values out of these so we can use them as indices
*/
minute = tm->tm_min -FIRST_MINUTE;
hour = tm->tm_hour -FIRST_HOUR;
dom = tm->tm_mday -FIRST_DOM;
month = tm->tm_mon +1 /* 0..11 -> 1..12 */ -FIRST_MONTH;
dow = tm->tm_wday -FIRST_DOW;
Debug(DSCH, ("[%ld] tick(%d,%d,%d,%d,%d) %s %s\n",
(long)getpid(), minute, hour, dom, month, dow,
doWild?" ":"No wildcard",doNonWild?" ":"Wildcard only"))
/* the dom/dow situation is odd. '* * 1,15 * Sun' will run on the
* first and fifteenth AND every Sunday; '* * * * Sun' will run *only*
* on Sundays; '* * 1,15 * *' will run *only* the 1st and 15th. this
* is why we keep 'e->dow_star' and 'e->dom_star'. yes, it's bizarre.
* like many bizarre things, it's the standard.
*/
for (u = db->head; u != NULL; u = u->next) {
for (e = u->crontab; e != NULL; e = e->next) {
Debug(DSCH|DEXT, ("user [%s:%lu:%lu:...] cmd=\"%s\"\n",
e->pwd->pw_name, (unsigned long)e->pwd->pw_uid,
(unsigned long)e->pwd->pw_gid, e->cmd))
if (bit_test(e->minute, minute) &&
bit_test(e->hour, hour) &&
bit_test(e->month, month) &&
( ((e->flags & DOM_STAR) || (e->flags & DOW_STAR))
? (bit_test(e->dow,dow) && bit_test(e->dom,dom))
: (bit_test(e->dow,dow) || bit_test(e->dom,dom))
)
) {
if ((doNonWild &&
!(e->flags & (MIN_STAR|HR_STAR))) ||
(doWild && (e->flags & (MIN_STAR|HR_STAR))))
job_add(e, u);
}
}
}
}
/*
* Set StartTime and clockTime to the current time.
* These are used for computing what time it really is right now.
* Note that clockTime is a unix wallclock time converted to minutes.
*/
static void
set_time(int initialize) {
struct tm tm;
static int isdst;
StartTime = time(NULL);
/* We adjust the time to GMT so we can catch DST changes. */
tm = *localtime(&StartTime);
if (initialize || tm.tm_isdst != isdst) {
isdst = tm.tm_isdst;
GMToff = get_gmtoff(&StartTime, &tm);
Debug(DSCH, ("[%ld] GMToff=%ld\n",
(long)getpid(), (long)GMToff))
}
clockTime = (StartTime + GMToff) / (time_t)SECONDS_PER_MINUTE;
}
/*
* Try to just hit the next minute.
*/
static void
cron_sleep(int target) {
int fd, nfds;
unsigned char poke;
struct timeval t1, t2, tv;
struct sockaddr_un s_un;
socklen_t sunlen;
static fd_set *fdsr;
gettimeofday(&t1, NULL);
t1.tv_sec += GMToff;
tv.tv_sec = (target * SECONDS_PER_MINUTE - t1.tv_sec) + 1;
tv.tv_usec = 0;
if (fdsr == NULL) {
fdsr = (fd_set *)calloc(howmany(cronSock + 1, NFDBITS),
sizeof(fd_mask));
}
while (timerisset(&tv) && tv.tv_sec 65) {
Debug(DSCH, ("[%ld] Target time=%ld, sec-to-wait=%ld\n",
(long)getpid(), (long)target*SECONDS_PER_MINUTE, tv.tv_sec))
poke = RELOAD_CRON | RELOAD_AT;
if (fdsr)
FD_SET(cronSock, fdsr);
/* Sleep until we time out, get a poke, or get a signal. */
nfds = select(cronSock + 1, fdsr, NULL, NULL, &tv);
if (nfds == 0)
break; /* timer expired */
if (nfds == -1 && errno != EINTR)
break; /* an error occurred */
if (nfds > 0) {
Debug(DSCH, ("[%ld] Got a poke on the socket\n",
(long)getpid()))
sunlen = sizeof(s_un);
fd = accept(cronSock, (struct sockaddr *)&s_un, &sunlen);
if (fd >= 0 && fcntl(fd, F_SETFL, O_NONBLOCK) == 0) {
(void) read(fd, &poke, 1);
close(fd);
if (poke & RELOAD_CRON) {
database.mtime = (time_t)0;
load_database(&database);
}
if (poke & RELOAD_AT) {
/*
* We run any pending at jobs right
* away so that "at now" really runs
* jobs immediately.
*/
gettimeofday(&t2, NULL);
at_database.mtime = (time_t)0;
if (scan_atjobs(&at_database, &t2))
atrun(&at_database,
batch_maxload, t2.tv_sec);
}
}
} else {
/* Interrupted by a signal. */
if (got_sighup) {
got_sighup = 0;
log_close();
}
if (got_sigchld) {
got_sigchld = 0;
sigchld_reaper();
}
}
/* Adjust tv and continue where we left off. */
gettimeofday(&t2, NULL);
t2.tv_sec += GMToff;
timersub(&t2, &t1, &t1);
timersub(&tv, &t1, &tv);
memcpy(&t1, &t2, sizeof(t1));
if (tv.tv_sec 0)
tv.tv_sec = 0;
if (tv.tv_usec 0)
tv.tv_usec = 0;
}
}
static void
sighup_handler(int x) {
got_sighup = 1;
}
static void
sigchld_handler(int x) {
got_sigchld = 1;
}
static void
quit(int x) {
(void) unlink(_PATH_CRON_PID);
_exit(0);
}
static void
sigchld_reaper(void) {
WAIT_T waiter;
PID_T pid;
do {
pid = waitpid(-1, &waiter, WNOHANG);
switch (pid) {
case -1:
if (errno == EINTR)
continue;
Debug(DPROC,
("[%ld] sigchld...no children\n",
(long)getpid()))
break;
case 0:
Debug(DPROC,
("[%ld] sigchld...no dead kids\n",
(long)getpid()))
break;
default:
Debug(DPROC,
("[%ld] sigchld...pid #%ld died, stat=%d\n",
(long)getpid(), (long)pid, WEXITSTATUS(waiter)))
break;
}
} while (pid > 0);
}
static void
parse_args(int argc, char *argv[]) {
int argch;
char *ep;
while (-1 != (argch = getopt(argc, argv, "l:nx:"))) {
switch (argch) {
case 'l':
errno = 0;
batch_maxload = strtod(optarg, &ep);
if (*ep != '\0' || ep == optarg || errno == ERANGE ||
batch_maxload 0) {
fprintf(stderr, "Illegal load average: %s\n",
optarg);
usage();
}
break;
case 'n':
NoFork = 1;
break;
case 'x':
if (!set_debug_flags(optarg))
usage();
break;
default:
usage();
}
}
}

cron.c