The function multiple starts immediately after add into cron

[austinov]

I'm trying to add function into CRON to running every minute:
c.AddFunc("*/1 * * * *", func() { log.Println("Run every minute") })

If I do it immediately after cron object was created, then code works as expected - the function will be executed every minute, starting at the beginning of the next minute.
But if I will add the function in a minute after the current (or later - after 2, 3 and more minutes), it begins to execute immediately after you add into the cron.
In addition, it executed as many times as the minutes passed between the creation of the cron and function was added.
For example, if you try to run the following code:

package main

import (
        "log"
        "time"
        "gopkg.in/robfig/cron.v2"
)

func main() {
        c := cron.New()
        c.Start()
        log.Println("Start CRON.")
        time.Sleep(2 * time.Minute)
        log.Println("Add function into CRON.")
        c.AddFunc("*/1 * * * *", func() { log.Println("Run every minute") })
        time.Sleep(5 * time.Second)
        c.Stop()
}

So, the function will call exactly 2 times immediately after adding into cron, because it took 2 minutes between the start of the cron (12:31:36) and adding the function into it (12:33:36).

2017/05/29 12:31:36 Start CRON.
2017/05/29 12:33:36 Add function into CRON.
2017/05/29 12:33:36 Run every minute
2017/05/29 12:33:36 Run every minute

If between execute c.Start() and c.AddFunc took 3 minutes, then we would see in the logs three calls Run every minute.
In my opinion, the first time the function should be executed at the beginning of the next minute - 12:34:00 and repeat every minute.

[austinov]

Excuse me, it was fixed in master, but not in gopkg.in/robfig/cron.v2.
Would you fix it in gopkg.in/robfig/cron.v2?

[robbbsen]

For me this is a downgrade of functionality. Think about I would like to update all of my jobs. I would've picked something like this:

var cronGlobal *cron.Cron

func refresh() {
	newCron := cron.New()
	// I would've started the new one first to ensure no interval gets missed
	newCron.Start()
	
	// Then I would've stopped the old one
	cronGlobal.Stop()
	
	// I could've added the jobs afterwards
	for _, job := range dbEntries {
		newCron.Add(job.Expression, job)
	}
	
	// Then I would've overwritten the global one
	cronGlobal = newCron
}

This way I could've been sure no interval gets missed while I'm setting up the new list. Because some of the items that are getting added to the new cron object are old ones from the previous cron object.

I hope it's clear what I'm talking about. Hope to find some other safe way.

[robfig]

I agree that it is a bug. v3 branch has this fix, and it has other fixes too. I recommend upgrading to it.