diff options
Diffstat (limited to 'vendor/github.com/robfig/cron/v3/doc.go')
| -rw-r--r-- | vendor/github.com/robfig/cron/v3/doc.go | 231 |
1 files changed, 231 insertions, 0 deletions
diff --git a/vendor/github.com/robfig/cron/v3/doc.go b/vendor/github.com/robfig/cron/v3/doc.go new file mode 100644 index 000000000..fa5d08b4d --- /dev/null +++ b/vendor/github.com/robfig/cron/v3/doc.go @@ -0,0 +1,231 @@ +/* +Package cron implements a cron spec parser and job runner. + +Installation + +To download the specific tagged release, run: + + go get github.com/robfig/cron/v3@v3.0.0 + +Import it in your program as: + + import "github.com/robfig/cron/v3" + +It requires Go 1.11 or later due to usage of Go Modules. + +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("30 * * * *", func() { fmt.Println("Every hour on the half hour") }) + c.AddFunc("30 3-6,20-23 * * *", func() { fmt.Println(".. in the range 3-6am, 8-11pm") }) + c.AddFunc("CRON_TZ=Asia/Tokyo 30 04 * * *", func() { fmt.Println("Runs at 04:30 Tokyo time every day") }) + c.AddFunc("@hourly", func() { fmt.Println("Every hour, starting an hour from now") }) + c.AddFunc("@every 1h30m", func() { fmt.Println("Every hour thirty, starting an hour thirty from now") }) + 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 5 space-separated fields. + + Field name | Mandatory? | Allowed values | Allowed special characters + ---------- | ---------- | -------------- | -------------------------- + 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 | * / , - ? + +Month and Day-of-week field values are case insensitive. "SUN", "Sun", and +"sun" are equally accepted. + +The specific interpretation of the format is based on the Cron Wikipedia page: +https://en.wikipedia.org/wiki/Cron + +Alternative Formats + +Alternative Cron expression formats support other fields like seconds. You can +implement that by creating a custom Parser as follows. + + cron.New( + cron.WithParser( + cron.NewParser( + cron.SecondOptional | cron.Minute | cron.Hour | cron.Dom | cron.Month | cron.Dow | cron.Descriptor))) + +Since adding Seconds is the most common modification to the standard cron spec, +cron provides a builtin function to do that, which is equivalent to the custom +parser you saw earlier, except that its seconds field is REQUIRED: + + cron.New(cron.WithSeconds()) + +That emulates Quartz, the most popular alternative Cron schedule format: +http://www.quartz-scheduler.org/documentation/quartz-2.x/tutorials/crontrigger.html + +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 1 1 * + @monthly | Run once a month, midnight, first of month | 0 0 1 * * + @weekly | Run once a week, midnight between Sat/Sun | 0 0 * * 0 + @daily (or @midnight) | Run once a day, midnight | 0 0 * * * + @hourly | Run once an hour, beginning of hour | 0 * * * * + +Intervals + +You may also schedule a job to execute at fixed intervals, starting at the time it's added +or 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 after +1 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 + +By default, all interpretation and scheduling is done in the machine's local +time zone (time.Local). You can specify a different time zone on construction: + + cron.New( + cron.WithLocation(time.UTC)) + +Individual cron schedules may also override the time zone they are to be +interpreted in by providing an additional space-separated field at the beginning +of the cron spec, of the form "CRON_TZ=Asia/Tokyo". + +For example: + + # Runs at 6am in time.Local + cron.New().AddFunc("0 6 * * ?", ...) + + # Runs at 6am in America/New_York + nyc, _ := time.LoadLocation("America/New_York") + c := cron.New(cron.WithLocation(nyc)) + c.AddFunc("0 6 * * ?", ...) + + # Runs at 6am in Asia/Tokyo + cron.New().AddFunc("CRON_TZ=Asia/Tokyo 0 6 * * ?", ...) + + # Runs at 6am in Asia/Tokyo + c := cron.New(cron.WithLocation(nyc)) + c.SetLocation("America/New_York") + c.AddFunc("CRON_TZ=Asia/Tokyo 0 6 * * ?", ...) + +The prefix "TZ=(TIME ZONE)" is also supported for legacy compatibility. + +Be aware that jobs scheduled during daylight-savings leap-ahead transitions will +not be run! + +Job Wrappers + +A Cron runner may be configured with a chain of job wrappers to add +cross-cutting functionality to all submitted jobs. For example, they may be used +to achieve the following effects: + + - Recover any panics from jobs (activated by default) + - Delay a job's execution if the previous run hasn't completed yet + - Skip a job's execution if the previous run hasn't completed yet + - Log each job's invocations + +Install wrappers for all jobs added to a cron using the `cron.WithChain` option: + + cron.New(cron.WithChain( + cron.SkipIfStillRunning(logger), + )) + +Install wrappers for individual jobs by explicitly wrapping them: + + job = cron.NewChain( + cron.SkipIfStillRunning(logger), + ).Then(job) + +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. + +Logging + +Cron defines a Logger interface that is a subset of the one defined in +github.com/go-logr/logr. It has two logging levels (Info and Error), and +parameters are key/value pairs. This makes it possible for cron logging to plug +into structured logging systems. An adapter, [Verbose]PrintfLogger, is provided +to wrap the standard library *log.Logger. + +For additional insight into Cron operations, verbose logging may be activated +which will record job runs, scheduling decisions, and added or removed jobs. +Activate it with a one-off logger as follows: + + cron.New( + cron.WithLogger( + cron.VerbosePrintfLogger(log.New(os.Stdout, "cron: ", log.LstdFlags)))) + + +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. +*/ +package cron |