Move status table to cron package (#7370)

vendor/github.com/gogs/cron/doc.go

@@ -0,0 +1,129 @@
+/*
+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, 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 immediately,
+and then 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.
+*/
+package cron