ReplaceCron - Upstart

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Launchpad entry: https://launchpad.net/products/upstart/+spec/replace-cron

Summary

This long-term goal of "upstart" is to act as a replacement for _nearly_ all job control services (e.g. init, inetd, cron, anacron, at). This specification proposes how the cron/anacron replacement functionality will work.

Rationale

This will permit jobs (aka services) to be run at a specific time or date.

Why do we want to do this?
- To create a consistent system for starting services and jobs timed or otherwise.
What advantage would 'upstart' have over 'cron'?
- It could start timed jobs only when necessary.
Doesn't this make 'upstart' overly complex?
- No, the only change that is needed is another event type.

Use cases

A backup system could be started on a specific time but only if the (necessary) filesystem is mounted. Otherwise it will skip its backup round.

Scope

This scope of this specification is limited to job definition and events.

Design

Initial version:

There would be a new sort of event.
on time TIME=hh:mm DAY_OF_WEEK=dow DATE=mm/dd/yy to start a job on a specific time/date

Cron compatibility

A new cron event
on cron MINUTE=mm HOUR=hh DOM=dd MONTH=mm DOW=w
- This allows a script to use normal cron times because of pattern matching

End version:

There would be a new sort of event.

on every ... to specify repeating events

on every hour
on every monday
on every year

on time hh:mm, on date mm/dd/yy, on day-of-week to define a specific time/date.

on time 12:00                   # every day
on date 10/12/12                # once in a lifetime a full day
on day-of-week 1                # every sunday

A time/date definition could have the special * character to define any...

on time *:30                    # every hour (on every day)
on date 10/12/*                 # every year a full day
on date */*/*                   # every day a full day

A time/date definition could have a range [1-3] to define multiple values.
- ```
on time [0-12]:00               # every hour AM (on every day)
```

A time/date definition could have a list {1,2,4} to define multiple non-continuous values.

on time *:{0,30}                # every half an hour (on every day)
on time {0:00,6:00,12:00,18:00} # every six hours

... at hh:mm, ... at mm/dd/yy, ... at monday... to allow combinations:

on every day at 12:00
on every year at monday         # a full day
on every year at monday at 5:{0,30}

A time hh:mm or at hh:mm event will only happen for a minute (or its logical range), unless or later or or earlier is specified
- ```
on every day at 12:00 or later  # not before 12:00
on every day at 6:00 or earlier # not after 6:00
```

Implementation

Code

events.h

Added:

/**
 * TIME_EVENT:
 *
 * Name of the event we generate every minute, which includes arguments and
 * environment indictating when the event was generated.
 **/
#define TIME_EVENT "time"

main.c main()

Modified:

        /* Process the event queue each time through the main loop */
        NIH_MUST (nih_main_loop_add_func (NULL, (NihMainLoopCb)event_poll,
                                          NULL));

+       /* Initialize the timers */
+       nih_timer_init();

        /* Read configuration */
        NIH_MUST (conf_source_new (NULL, CONFFILE, CONF_FILE));
        NIH_MUST (conf_source_new (NULL, CONFDIR, CONF_JOB_DIR));

m       /* Generate and run the startup and time event or read the state from the
         * init daemon that exec'd us
         */
        if (! restart) {
                NIH_MUST (event_new (NULL, STARTUP_EVENT, NULL));
+               timer_handler(NULL,NULL);
        } else {
                sigset_t mask;

                /* We're ok to receive signals again */
                sigemptyset (&mask);
                sigprocmask (SIG_SETMASK, &mask, NULL);
        }