Running a Go method using cron

I'm trying to write a program that will continuously call a method at a certain time interval. I'm using a cron library to try and achieve this but when I run the program it just executes and finishes with out any output.

Below is a basic example of what I'm trying to do.

Assistance greatly appreciated!

package main

import (
    "fmt"
	"github.com/robfig/cron"
)

func main() {
    c := cron.New()
    c.AddFunc("1 * * * * *", RunEverySecond)
    c.Start()
}

func RunEverySecond() {
    fmt.Println("----")
}

You can wait for the OS to signal you, e.g. CTRL-C from the user. Also your cron expression was for every minute, i.e. only where seconds == 1.

package main

import (
	"fmt"
	"os"
	"os/signal"
	"time"

	"github.com/robfig/cron"
)

func main() {
	c := cron.New()
	c.AddFunc("* * * * * *", RunEverySecond)
	go c.Start()
	sig := make(chan os.Signal)
	signal.Notify(sig, os.Interrupt, os.Kill)
	<-sig

}

func RunEverySecond() {
	fmt.Printf("%v\n", time.Now())
}

As you can see c.Start() runs in another goroutine, so the call to c.Start returns immediately. https://github.com/robfig/cron/blob/master/cron.go#L125

So your program finishes earlier than you see any output. You may add something like time.Sleep(1 * minute) or have a close channel for this (or just <-make(chan struct{}) to wait eternally)

Using an external package for this is overkill, the time package has everything you need:

package main

import (
	"fmt"
	"time"
)

func main() {
	go func() {
		c := time.Tick(1 * time.Second)
		for range c {
			// Note this purposfully runs the function
			// in the same goroutine so we make sure there is
			// only ever one. If it might take a long time and
			// it's safe to have several running just add "go" here.
			RunEverySecond()
		}
	}()

	// Other processing or the rest of your program here.
	time.Sleep(5 * time.Second)

	// Or to block forever:
	//select {}
	// However, if doing that you could just stick the above for loop
	// right here without dropping it into a goroutine.
}

func RunEverySecond() {
	fmt.Println("----")
}

<kbd>playground</kbd>

or something like this using sync wait group.

package main

import (
	"fmt"
	"sync"

	"github.com/robfig/cron"
)

// RunEverySecond is to run all the time.
func RunEverySecond() {
	fmt.Println("----")
	//wg.Done() // Does not release the waitgroup.
}

func main() {
	wg := &sync.WaitGroup{}
	wg.Add(1)
	c := cron.New()
	c.AddFunc("@every 1s", RunEverySecond)
	c.Start()
	wg.Wait() // This guarantees this program never exits so cron can keep running as per the cron interval.
}

Just make sure to keep the application always running, ie:

func main() {
	cronJob := cron.New()
	cronJob.Start()
	cronJob.AddFunc("* * * * * ?", PushConfigs)
	for {
	}
}