Ability to register for events associated with jobs starting immediately

[drwpls]

What does this do?

This commit add some functions to support register events for job which is on creating and run immediately.

Which issue(s) does this PR fix/relate to?

Job run immediately doesn't have before/after/onErr/onNoErr events.

List any changes that modify/break current functionality

No

Have you included tests for your changes?

Yes, it's in scheduler_test.go

Did you document any new/modified functionality?

Yes, in function header

Notes

Consider to change RegisterEventListeners to change only current job

[JohnRoesler]

This is a handy addition. Although, nothing in the current code prevents you from having event listeners on a job that starts immediately.

package main

import (
	"log"
	"time"

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

func main() {
	s := gocron.NewScheduler(time.UTC)
	j, err := s.Every(1).Seconds().StartImmediately().Do(func() {})
	if err != nil {
		log.Fatal(err)
	}
	j.RegisterEventListeners(
		gocron.BeforeJobRuns(func(jobName string) {
			// do something
		}),
	)
	s.StartBlocking()
}

[drwpls]

This is a handy addition. Although, nothing in the current code prevents you from having event listeners on a job that starts immediately.

package main

import (
	"log"
	"time"

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

func main() {
	s := gocron.NewScheduler(time.UTC)
	j, err := s.Every(1).Seconds().StartImmediately().Do(func() {})
	if err != nil {
		log.Fatal(err)
	}
	j.RegisterEventListeners(
		gocron.BeforeJobRuns(func(jobName string) {
			// do something
		}),
	)
	s.StartBlocking()
}

Your code will only work if the startBlocking statement runs after setting up the jobs, and it can't register events for individual jobs.

One more question: why did you define eventListenerFunc signature contain jobName (string) instead of *Job

[JohnRoesler]

Your code will only work if the startBlocking statement runs after setting up the jobs, and it can't register events for individual jobs.

Correct, that you have to setup all the jobs first and then start. However, that does set the event listeners for an individual job. It's being called on the Job j.

why did you define eventListenerFunc signature contain jobName (string) instead of *Job

To avoid race conditions with the Job being a pointer.

Are there other fields that would be useful in the event listeners? I can definitely see how more info could be useful / better. I'd be happy to consider enhancements in v2 👍

[drwpls]

If you set up 2 jobs, both got event registered. I don't think that is for individual job.
https://github.com/go-co-op/gocron/blob/30921b708f1ef7910842cc63fc27fe383c7e5d81/scheduler.go#L1517C1-L1528C2

Correct, that you have to setup all the jobs first and then start. However, that does set the event listeners for an individual job. It's being called on the Job j.

You already have mutex in job structure.

To avoid race conditions with the Job being a pointer.