How to find a particular running cron jobs with github.com/robfig/cron?

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How do we look for particular running cron jobs within github.com/robfig/cron?

In a notification service, where we store notifications in database, each notification either is to send (to user) immediately or scheduled.

The scheduled ones are sent using cron jobs. If a scheduled notification was deleted before it sent, how do we look for the cron job to be deleted?

go cron
1 Answers

With github.com/robfig/cron/v3 You can use Cron.Entry.

This is a basic usage example:

job := cron.FuncJob(func() {
    fmt.Println("Hello Cron")
})

c := cron.New(/* options */) 
entryId := c.Schedule(cron.Every(time.Second*5), job)

// Find the job entry
entry := c.Entry(entryId)
// ... here you can inspect the job `entry`

// Removes the entry, it won't run again
c.Remove(entryId)

cron.FuncJob is actually just a wrapper around func(). In case you need more complex behavior, or state, you can implement the Job interface yourself:

type myJob struct{}

func (j *myJob) Run() {
    fmt.Println("foo")
}

Then you can fetch the specific instance of your job by type-asserting:

j := c.Entry(id).Job.(*myJob)
// ... do something with the *myJob instance

You can also customize the schedule, by implementing Schedule interface:

type mySchedule struct{}

// Next returns the next activation time, later than the given time.
// Next is invoked initially, and then each time the job is run.
func (s *mySchedule) Next(time.Time) time.Time {
    return time.Now().Add(time.Second*5)
}

And then use it all like:

c := cron.New(/* options */) 
entryId := c.Schedule(&mySchedule{}, &myJob{})

If you use an earlier version of the package, unfortunately you can't get a single entry by id and Cron.Schedule doesn't assign ids either. You must manage a lookup table yourself. If possible, I recommend upgrading to v3.

user_41088030
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