[BUG] - Potential Memory Leak Due to Timer Creation in AfterFunc and selectExecJobsOutForRescheduling

[hayotbisonai]

Describe the bug

I've noticed a potential memory issue related to the use of timers and goroutines in the AfterFunc implementation in the clockwork package and the job rescheduling process in the scheduler. When profiling the application, I observed significant memory consumption, particularly related to time.goFunc and goroutines created by AfterFunc.

Key points:

• The AfterFunc call creates a new goroutine each time a timer is set, and this can lead to many goroutines being created and left hanging if they are not stopped or properly handled.
• The frequent scheduling and rescheduling of jobs in selectExecJobsOutForRescheduling might contribute to the problem due to timer and goroutine buildup.

Profile Data:

Showing nodes accounting for 239.24MB, 76.13% of 314.25MB total
Dropped 126 nodes (cum <= 1.57MB)
Showing top 10 nodes out of 107
      flat  flat%   sum%        cum   cum%
   79.66MB 25.35% 25.35%    79.66MB 25.35%  time.goFunc
   31.43MB 10.00% 35.35%    31.43MB 10.00%  github.com/go-co-op/gocron/v2.(*scheduler).selectNewJob
   31.01MB  9.87% 45.22%    31.01MB  9.87%  runtime.malg
   21.50MB  6.84% 52.06%    34.30MB 10.92%  context.withCancel (inline)
   19.01MB  6.05% 58.11%    21.05MB  6.70%  github.com/go-co-op/gocron/v2.(*scheduler).selectExecJobsOutForRescheduling

As seen, time.goFunc and the scheduling-related functions are taking a substantial amount of memory and keeps growing

To Reproduce

Steps to reproduce the behavior:

Version

Expected behavior

Additional context

[JohnRoesler]

Thanks for reporting @hayotbisonai - I have started looking into this a few times, but haven't been able come to a solution. Thanks for your patience.

[JohnRoesler]

@hayotbisonai can you share what code you're running and the profiling you ran to generate the above?

[JohnRoesler]

If anyone is able to provide code reproducing this bug, I would appreciate. I have tried running with quite a few scenarios, and thousands of jobs on the scheduler and I am not able to reproduce.

Example of one test:

package main

import (
	"log"
	"net/http"
	_ "net/http/pprof"
	"time"

	"github.com/go-co-op/gocron/v2"
)

func main() {

	go func() {
		log.Println(http.ListenAndServe("localhost:6060", nil))
	}()

	s, err := gocron.NewScheduler()
	if err != nil {
		log.Fatal(err)
	}

	for i := 0; i < 1000; i++ {
		_, err = s.NewJob(
			gocron.DurationJob(time.Second),
			gocron.NewTask(func() {
				log.Println("Hello, world!")
			}),
		)
	}

	s.Start()
	select {}
}

Please comment or reopen if you're able to provide details on reproduction 👍 Thanks!