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Add new functionality and syntax to cron(1) to allow to run jobs at a

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given interval, which is counted in seconds since exit of the previous
invocation of the job. Example user crontab entry:

@25	sleep 10

The example will launch 'sleep 10' every 35 seconds. This is a rather
useless example above, but clearly explains the functionality.

The practical goal here is to avoid overlap of previous job invocation
to a new one, or to avoid too short interval(s) for jobs that last long
and doesn't have any point of immediate launch soon after previous run.

Another useful effect of interval jobs can be noticed when a cluster of
machines periodically communicates with a single node. Running the task
time based creates too much load on the node. Running interval based
spreads invocations across machines in cluster. Note that -j/-J won't
help in this case.

Sponsored by:	Netflix
This commit is contained in:
glebius 2018-06-07 22:38:40 +00:00
parent 1dfe30dc12
commit bb27a539de
5 changed files with 88 additions and 14 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

35
usr.sbin/cron/cron/cron.c
View File

@ -46,7 +46,9 @@ static void usage(void),
parse_args(int c, char *v[]);
static int run_at_secres(cron_db *);
static void find_interval_entry(pid_t);
static cron_db database;
static time_t last_time = 0;
static int dst_enabled = 0;
static int dont_daemonize = 0;
@ -100,7 +102,6 @@ main(argc, argv)
int argc;
char *argv[];
{
cron_db database;
int runnum;
int secres1, secres2;
struct tm *tm;
@ -154,8 +155,8 @@ main(argc, argv)
database.mtime = (time_t) 0;
load_database(&database);
secres1 = secres2 = run_at_secres(&database);
run_reboot_jobs(&database);
cron_sync(secres1);
run_reboot_jobs(&database);
runnum = 0;
while (TRUE) {
# if DEBUGGING
@ -210,6 +211,9 @@ run_reboot_jobs(db)
if (e->flags & WHEN_REBOOT) {
job_add(e, u);
}
if (e->flags & INTERVAL) {
e->lastexit = TargetTime;
}
}
}
(void) job_runqueue();
@ -313,6 +317,13 @@ cron_tick(cron_db *db, int secres)
env_get("LOGNAME", e->envp),
e->uid, e->gid, e->cmd))
if (e->flags & INTERVAL) {
if (e->lastexit > 0 &&
TargetTime >= e->lastexit + e->interval)
job_add(e, u);
continue;
}
if ( diff != 0 && (e->flags & (RUN_AT|NOT_UNTIL)) ) {
if (bit_test(e->second, otzsecond)
&& bit_test(e->minute, otzminute)
@ -489,6 +500,7 @@ sigchld_handler(int x)
("[%d] sigchld...no dead kids\n", getpid()))
return;
default:
find_interval_entry(pid);
Debug(DPROC,
("[%d] sigchld...pid #%d died, stat=%d\n",
getpid(), pid, WEXITSTATUS(waiter)))
@ -557,9 +569,26 @@ run_at_secres(cron_db *db)
for (u = db->head; u != NULL; u = u->next) {
for (e = u->crontab; e != NULL; e = e->next) {
if ((e->flags & SEC_RES) != 0)
if ((e->flags & (SEC_RES | INTERVAL)) != 0)
return 1;
}
}
return 0;
}
static void
find_interval_entry(pid_t pid)
{
user *u;
entry *e;
for (u = database.head; u != NULL; u = u->next) {
for (e = u->crontab; e != NULL; e = e->next) {
if ((e->flags & INTERVAL) && e->child == pid) {
e->lastexit = time(NULL);
e->child = 0;
break;
}
}
}
}

24
usr.sbin/cron/cron/cron.h
View File

@ -168,19 +168,29 @@ typedef struct _entry {
#endif
char **envp;
char *cmd;
bitstr_t bit_decl(second, SECOND_COUNT);
bitstr_t bit_decl(minute, MINUTE_COUNT);
bitstr_t bit_decl(hour, HOUR_COUNT);
bitstr_t bit_decl(dom, DOM_COUNT);
bitstr_t bit_decl(month, MONTH_COUNT);
bitstr_t bit_decl(dow, DOW_COUNT);
union {
struct {
bitstr_t bit_decl(second, SECOND_COUNT);
bitstr_t bit_decl(minute, MINUTE_COUNT);
bitstr_t bit_decl(hour, HOUR_COUNT);
bitstr_t bit_decl(dom, DOM_COUNT);
bitstr_t bit_decl(month, MONTH_COUNT);
bitstr_t bit_decl(dow, DOW_COUNT);
};
struct {
time_t lastexit;
time_t interval;
pid_t child;
};
};
int flags;
#define DOM_STAR 0x01
#define DOW_STAR 0x02
#define WHEN_REBOOT 0x04
#define RUN_AT 0x08
#define RUN_AT 0x08
#define NOT_UNTIL 0x10
#define SEC_RES 0x20
#define INTERVAL 0x40
time_t lastrun;
} entry;

12
usr.sbin/cron/cron/do_command.c
View File

@ -47,6 +47,8 @@ do_command(e, u)
entry *e;
user *u;
{
pid_t pid;
Debug(DPROC, ("[%d] do_command(%s, (%s,%d,%d))\n",
getpid(), e->cmd, u->name, e->uid, e->gid))
@ -57,9 +59,11 @@ do_command(e, u)
* vfork() is unsuitable, since we have much to do, and the parent
* needs to be able to run off and fork other processes.
*/
switch (fork()) {
switch ((pid = fork())) {
case -1:
log_it("CRON",getpid(),"error","can't fork");
if (e->flags & INTERVAL)
e->lastexit = time(NULL);
break;
case 0:
/* child process */
@ -70,6 +74,12 @@ do_command(e, u)
break;
default:
/* parent process */
Debug(DPROC, ("[%d] main process forked child #%d, "
"returning to work\n", getpid(), pid))
if (e->flags & INTERVAL) {
e->lastexit = 0;
e->child = pid;
}
break;
}
Debug(DPROC, ("[%d] main process returning to work\n", getpid()))

21
usr.sbin/cron/crontab/crontab.5
View File

@ -17,7 +17,7 @@
.\"
.\" $FreeBSD$
.\"
.Dd January 5, 2016
.Dd June 6, 2018
.Dt CRONTAB 5
.Os
.Sh NAME
@ -220,7 +220,10 @@ would cause a command to be run at 4:30 am on the 1st and 15th of each
month, plus every Friday.
.Pp
Instead of the first five fields,
one of eight special strings may appear:
a line may start with
.Sq @
symbol followed either by one of eight special strings or by a numeric value.
The recognized special strings are:
.Bd -literal -offset indent
string meaning
------ -------
@ -235,6 +238,16 @@ string meaning
@every_minute Run once a minute, "*/1 * * * *".
@every_second Run once a second.
.Ed
.Pp
The
.Sq @
symbol followed by a numeric value has a special notion of running
a job that much seconds after completion of previous invocation of
the job.
Unlike regular syntax, it guarantees not to overlap two or more
invocations of the same job.
The first run is scheduled specified amount of seconds after cron
has started.
.Sh EXAMPLE CRON FILE
.Bd -literal
@ -251,6 +264,8 @@ MAILTO=paul
0 22 * * 1-5 mail -s "It's 10pm" joe%Joe,%%Where are your kids?%
23 0-23/2 * * * echo "run 23 minutes after midn, 2am, 4am ..., everyday"
5 4 * * sun echo "run at 5 after 4 every sunday"
# run at 5 minutes intervals, no matter how long it takes
@300 svnlite up /usr/src
.Ed
.Sh SEE ALSO
.Xr crontab 1 ,
@ -292,7 +307,7 @@ either).
.Pp
All of the
.Sq @
commands that can appear in place of the first five fields
directives that can appear in place of the first five fields
are extensions.
.Sh AUTHORS
.An Paul Vixie Aq Mt paul@vix.com

10
usr.sbin/cron/lib/entry.c
View File

@ -132,6 +132,9 @@ load_entry(file, error_func, pw, envp)
}
if (ch == '@') {
long interval;
char *endptr;
/* all of these should be flagged and load-limited; i.e.,
* instead of @hourly meaning "0 * * * *" it should mean
* "close to the front of every hour but not 'til the
@ -209,6 +212,13 @@ load_entry(file, error_func, pw, envp)
bit_nset(e->dom, 0, (LAST_DOM-FIRST_DOM+1));
bit_nset(e->month, 0, (LAST_MONTH-FIRST_MONTH+1));
bit_nset(e->dow, 0, (LAST_DOW-FIRST_DOW+1));
} else if (*cmd != '\0' &&
(interval = strtol(cmd, &endptr, 10)) > 0 &&
*endptr == '\0') {
Debug(DPARS, ("load_entry()... %ld seconds "
"since last run\n", interval))
e->interval = interval;
e->flags = INTERVAL;
} else {
ecode = e_timespec;
goto eof;