README
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Documentation
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Overview ¶
This library implements a cron spec parser and runner. See the README for more details.
Package cron implements a cron spec parser and job runner.
Usage ¶
Callers may register Funcs to be invoked on a given schedule. Cron will run them in their own goroutines.
c := cron.New()
c.AddFunc("0 30 * * * *", func() { fmt.Println("Every hour on the half hour") })
c.AddFunc("@hourly", func() { fmt.Println("Every hour") })
c.AddFunc("@every 1h30m", func() { fmt.Println("Every hour thirty") })
c.Start()
..
// Funcs are invoked in their own goroutine, asynchronously.
...
// Funcs may also be added to a running Cron
c.AddFunc("@daily", func() { fmt.Println("Every day") })
..
// Inspect the cron job entries' next and previous run times.
inspect(c.Entries())
..
c.Stop() // Stop the scheduler (does not stop any jobs already running).
CRON Expression Format ¶
A cron expression represents a set of times, using 6 space-separated fields.
Field name | Mandatory? | Allowed values | Allowed special characters ---------- | ---------- | -------------- | -------------------------- Seconds | Yes | 0-59 | * / , - Minutes | Yes | 0-59 | * / , - Hours | Yes | 0-23 | * / , - Day of month | Yes | 1-31 | * / , - ? Month | Yes | 1-12 or JAN-DEC | * / , - Day of week | Yes | 0-6 or SUN-SAT | * / , - ?
Note: Month and Day-of-week field values are case insensitive. "SUN", "Sun", and "sun" are equally accepted.
Special Characters ¶
Asterisk ( * )
The asterisk indicates that the cron expression will match for all values of the field; e.g., using an asterisk in the 5th field (month) would indicate every month.
Slash ( / )
Slashes are used to describe increments of ranges. For example 3-59/15 in the 1st field (minutes) would indicate the 3rd minute of the hour and every 15 minutes thereafter. The form "*\/..." is equivalent to the form "first-last/...", that is, an increment over the largest possible range of the field. The form "N/..." is accepted as meaning "N-MAX/...", that is, starting at N, use the increment until the end of that specific range. It does not wrap around.
Comma ( , )
Commas are used to separate items of a list. For example, using "MON,WED,FRI" in the 5th field (day of week) would mean Mondays, Wednesdays and Fridays.
Hyphen ( - )
Hyphens are used to define ranges. For example, 9-17 would indicate every hour between 9am and 5pm inclusive.
Question mark ( ? )
Question mark may be used instead of '*' for leaving either day-of-month or day-of-week blank.
Predefined schedules ¶
You may use one of several pre-defined schedules in place of a cron expression.
Entry | Description | Equivalent To ----- | ----------- | ------------- @yearly (or @annually) | Run once a year, midnight, Jan. 1st | 0 0 0 1 1 * @monthly | Run once a month, midnight, first of month | 0 0 0 1 * * @weekly | Run once a week, midnight on Sunday | 0 0 0 * * 0 @daily (or @midnight) | Run once a day, midnight | 0 0 0 * * * @hourly | Run once an hour, beginning of hour | 0 0 * * * *
Intervals ¶
You may also schedule a job to execute at fixed intervals. This is supported by formatting the cron spec like this:
@every <duration>
where "duration" is a string accepted by time.ParseDuration (http://golang.org/pkg/time/#ParseDuration).
For example, "@every 1h30m10s" would indicate a schedule that activates every 1 hour, 30 minutes, 10 seconds.
Note: The interval does not take the job runtime into account. For example, if a job takes 3 minutes to run, and it is scheduled to run every 5 minutes, it will have only 2 minutes of idle time between each run.
Time zones ¶
All interpretation and scheduling is done in the machine's local time zone (as provided by the Go time package (http://www.golang.org/pkg/time).
Be aware that jobs scheduled during daylight-savings leap-ahead transitions will not be run!
Thread safety ¶
Since the Cron service runs concurrently with the calling code, some amount of care must be taken to ensure proper synchronization.
All cron methods are designed to be correctly synchronized as long as the caller ensures that invocations have a clear happens-before ordering between them.
Implementation ¶
Cron entries are stored in an array, sorted by their next activation time. Cron sleeps until the next job is due to be run.
Upon waking:
- it runs each entry that is active on that second
- it calculates the next run times for the jobs that were run
- it re-sorts the array of entries by next activation time.
- it goes to sleep until the soonest job.
Index ¶
Constants ¶
This section is empty.
Variables ¶
This section is empty.
Functions ¶
This section is empty.
Types ¶
type ConstantDelaySchedule ¶
ConstantDelaySchedule represents a simple recurring duty cycle, e.g. "Every 5 minutes". It does not support jobs more frequent than once a second.
func Every ¶
func Every(duration time.Duration) ConstantDelaySchedule
Every returns a crontab Schedule that activates once every duration. Delays of less than a second are not supported (will round up to 1 second). Any fields less than a Second are truncated.
type Cron ¶
type Cron struct {
// contains filtered or unexported fields
}
Cron keeps track of any number of entries, invoking the associated func as specified by the schedule. It may be started, stopped, and the entries may be inspected while running.
type Entry ¶
type Entry struct {
// The schedule on which this job should be run.
Schedule Schedule
// The next time the job will run. This is the zero time if Cron has not been
// started or this entry's schedule is unsatisfiable
Next time.Time
// The last time this job was run. This is the zero time if the job has never
// been run.
Prev time.Time
// The Job to run.
Job Job
}
Entry consists of a schedule and the func to execute on that schedule.
type Schedule ¶
type Schedule interface {
// Return the next activation time, later than the given time.
// Next is invoked initially, and then each time the job is run.
Next(time.Time) time.Time
}
The Schedule describes a job's duty cycle.
type SpecSchedule ¶
type SpecSchedule struct {
Second, Minute, Hour, Dom, Month, Dow uint64
}
SpecSchedule specifies a duty cycle (to the second granularity), based on a traditional crontab specification. It is computed initially and stored as bit sets.
Source Files