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cron
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README¶
Documentation¶
Overview¶
Package cron implements a cron spec parser and job runner.
Usage¶
Callers may register Funcs to be invoked on a given schedule. Cron will runthem 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 Cronc.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 thefield; e.g., using an asterisk in the 5th field (month) would indicate everymonth.
Slash ( / )
Slashes are used to describe increments of ranges. For example 3-59/15 in the1st field (minutes) would indicate the 3rd minute of the hour and every 15minutes 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 theincrement 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" inthe 5th field (day of week) would mean Mondays, Wednesdays and Fridays.
Hyphen ( - )
Hyphens are used to define ranges. For example, 9-17 would indicate everyhour between 9am and 5pm inclusive.
Question mark ( ? )
Question mark may be used instead of '*' for leaving either day-of-month orday-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 between Sat/Sun | 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, starting at the time it's addedor cron is run. 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 after1 hour, 30 minutes, 10 seconds, and then every interval after that.
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 (asprovided by the Go time package (http://www.golang.org/pkg/time).
Be aware that jobs scheduled during daylight-savings leap-ahead transitions willnot be run!
Thread safety¶
Since the Cron service runs concurrently with the calling code, some amount ofcare must be taken to ensure proper synchronization.
All cron methods are designed to be correctly synchronized as long as the callerensures that invocations have a clear happens-before ordering between them.
Implementation¶
Cron entries are stored in an array, sorted by their next activation time. Cronsleeps 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¶
typeConstantDelaySchedule¶
ConstantDelaySchedule represents a simple recurring duty cycle, e.g. "Every 5 minutes".It does not support jobs more frequent than once a second.
funcEvery¶
func Every(durationtime.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.
typeCron¶
Cron keeps track of any number of entries, invoking the associated func asspecified by the schedule. It may be started, stopped, and the entries maybe inspected while running.
funcNewWithLocation¶added inv1.1.0
NewWithLocation returns a new Cron job runner.
func (*Cron)Run¶added inv1.1.0
func (c *Cron) Run()
Run the cron scheduler, or no-op if already running.
typeEntry¶
type Entry struct {// The schedule on which this job should be run.ScheduleSchedule// The next time the job will run. This is the zero time if Cron has not been// started or this entry's schedule is unsatisfiableNexttime.Time// The last time this job was run. This is the zero time if the job has never// been run.Prevtime.Time// The Job to run.JobJob}Entry consists of a schedule and the func to execute on that schedule.
typeParseOption¶added inv1.1.0
type ParseOptionint
Configuration options for creating a parser. Most options specify whichfields should be included, while others enable features. If a field is notincluded the parser will assume a default value. These options do not changethe order fields are parse in.
const (SecondParseOption = 1 <<iota// Seconds field, default 0Minute// Minutes field, default 0Hour// Hours field, default 0Dom// Day of month field, default *Month// Month field, default *Dow// Day of week field, default *DowOptional// Optional day of week field, default *Descriptor// Allow descriptors such as @monthly, @weekly, etc.)
typeParser¶added inv1.1.0
type Parser struct {// contains filtered or unexported fields}A custom Parser that can be configured.
funcNewParser¶added inv1.1.0
func NewParser(optionsParseOption)Parser
Creates a custom Parser with custom options.
// Standard parser without descriptorsspecParser := NewParser(Minute | Hour | Dom | Month | Dow)sched, err := specParser.Parse("0 0 15 */3 *")// Same as above, just excludes time fieldssubsParser := NewParser(Dom | Month | Dow)sched, err := specParser.Parse("15 */3 *")// Same as above, just makes Dow optionalsubsParser := NewParser(Dom | Month | DowOptional)sched, err := specParser.Parse("15 */3")typeSchedule¶
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.
funcParse¶
Parse returns a new crontab schedule representing the given spec.It returns a descriptive error if the spec is not valid.
It accepts
- Full crontab specs, e.g. "* * * * * ?"
- Descriptors, e.g. "@midnight", "@every 1h30m"
funcParseStandard¶added inv1.1.0
ParseStandard returns a new crontab schedule representing the given standardSpec(https://en.wikipedia.org/wiki/Cron). It differs from Parse requiring to alwayspass 5 entries representing: minute, hour, day of month, month and day of week,in that order. It returns a descriptive error if the spec is not valid.
It accepts
- Standard crontab specs, e.g. "* * * * ?"
- Descriptors, e.g. "@midnight", "@every 1h30m"
typeSpecSchedule¶
type SpecSchedule struct {Second, Minute, Hour, Dom, Month, Dowuint64}SpecSchedule specifies a duty cycle (to the second granularity), based on atraditional crontab specification. It is computed initially and stored as bit sets.
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