Spawning multiple jobs in a loop

[ottramst]

Hey guys,

Thanks for the awesome project!

Just some background - I'm a bit of a newbie when it comes to goroutines, channels and all that magic. So bare with me here.
I have a small question about "spawning" jobs in a loop.

My end goal is to spawn multiple jobs based on an array (doesn't matter - strings, int's etc):

func main() {

	a := []int{1, 2, 3}

	s := gocron.NewScheduler(time.UTC)

	for _, i := range a {
		s.Every("1s").Do(func() { fmt.Println(i) })
	}

	s.StartBlocking()
}

This gives me output

3
3
3
...

So it seems that only the last of the loop is actually passed to the scheduler. Any advice here?

Thanks!

[JohnRoesler]

Hi @ottramst glad you are enjoying the project! And we were all there once (as newbies)! 😁

This one is definitely sneaky and has to do with how the range values work in Go. Because you're passing in a function func() { fmt.Println(i) } the value of i isn't resolved immediately and when it is the value is 3, the final value in your loop. You can make it work the way you are desiring by copying the iterator value or passing it as a parameter to your function:

copy iterator

package main

import (
	"fmt"
	"log"
	"time"

	"github.com/go-co-op/gocron"
)

func main() {

	a := []int{1, 2, 3}

	s := gocron.NewScheduler(time.UTC)

	for _, i := range a {
		j := i
		_, err := s.Every("1s").Do(func() { fmt.Println(j) })
		if err != nil {
			log.Fatalln(err)
		}
	}

	s.StartBlocking()
}

as func param

package main

import (
	"fmt"
	"log"
	"time"

	"github.com/go-co-op/gocron"
)

func main() {

	a := []int{1, 2, 3}

	s := gocron.NewScheduler(time.UTC)

	for _, i := range a {
		_, err := s.Every("1s").Do(func(j int) { fmt.Println(j) }, i)
		if err != nil {
			log.Fatalln(err)
		}
	}

	s.StartBlocking()
}

[ottramst]

Thank you for this simple explanation!

[JohnRoesler]

You're very welcome 👍