2021/08/23，Golang 定时任务 是讲通过 Golang 原生的 time.Ticker 实现定时任务，本文介绍的是通过第三方库 robfig/cron 实现定时任务。
概述
- 代码：robfig/cron
- 文档： https://godoc.org/github.com/robfig/cron
标准 Cron 表达式 分成 5 段：分 minutes、时 hours、日 day of month、月 month、周 day of week。
robfig/cron v2 默认支持 6 个字段（包括秒 seconds），从 v3 开始又回到默认 5 个字段（需要做以下显式声明：cron.New(cron.WithSeconds())）。
type SpecSchedule struct {
Second, Minute, Hour, Dom, Month, Dow uint64
}
使用
// Seconds field, required
cron.New(cron.WithSeconds())
// Seconds field, optional
cron.New(cron.WithParser(cron.NewParser(
cron.SecondOptional | cron.Minute | cron.Hour | cron.Dom | cron.Month | cron.Dow | cron.Descriptor,
)))
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).
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 | * / , - ?
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 * * * *
