Prevent the main() function from terminating before goroutines finish in Golang
As already mentioned sync.WaitGroup
is a right way in production code. But when developing for test and debug purposes you can just add select{}
statement at the end or the main()
.
func main(){
go routine()
...
select{}
}
main()
then never returns and you would kill it with for example Ctrl-C
. It isn't idiomatic, never used in production, but just very quick easy hack when developing.
Simplest, cleanest and "scalable" way to do it is to use a sync.WaitGroup
:
var wg = &sync.WaitGroup{}
func printElo() {
defer wg.Done()
fmt.Printf("Elo\n")
}
func printHello() {
defer wg.Done()
fmt.Printf("Hello\n")
}
func main() {
fmt.Printf("This will print.")
i := 0
for i < 10 {
wg.Add(1)
go printElo()
wg.Add(1)
go printHello()
i++
}
wg.Wait()
}
Output (try it on the Go Playground):
This will print.Hello
Elo
Hello
Elo
Hello
Elo
Hello
Elo
Hello
Elo
Hello
Elo
Hello
Elo
Hello
Elo
Hello
Elo
Hello
Elo
Simple "rules" to follow when doing it with sync.WaitGroup
:
- call
WaitGroup.Add()
in the "original" goroutine (that starts a new) before thego
statement - recommended to call
WaitGroup.Done()
deferred, so it gets called even if the goroutine panics - if you want to pass
WaitGroup
to other functions (and not use a package level variable), you must pass a pointer to it, else theWaitGroup
(which is a struct) would be copied, and theDone()
method called on the copy wouldn't be observed on the original
You can use sync package and take a look at waitgroups
. You can take a look at a working Goplayground I set up.
Essentially
package main
import (
"fmt"
"sync"
)
//Takes a reference to the wg and sleeps when work is done
func printElo(wg *sync.WaitGroup) {
fmt.Printf("Elo\n")
defer wg.Done()
}
//Takes a reference to the wg and sleeps when work is done
func printHello(wg *sync.WaitGroup) {
fmt.Printf("Hello\n")
defer wg.Done()
}
func main() {
//Create a new WaitGroup
var wg sync.WaitGroup
fmt.Println("This will print.")
for i := 0; i < 10; i++ {
//Add a new entry to the waitgroup
wg.Add(1)
//New Goroutine which takes a reference to the wg
go printHello(&wg)
//Add a new entry to the waitgroup
wg.Add(1)
//New Goroutine which takes a reference to the wg
go printElo(&wg)
}
//Wait until everything is done
wg.Wait()
}