Here's a simple example of what I mean
package main
import (
"sync"
"testing"
"time"
)
func TestWaitGroup(t *testing.T) {
var wg sync.WaitGroup
quitSig := make(chan struct{})
go func(wg sync.WaitGroup, quitChan, chan struct{}) {
defer func() {
t.Log("Done...")
wg.Done()
t.Log("Done!")
}()
t.Log("waiting for quit channel signal...")
<-quitChan
t.Log("signal received")
}(wg, quitSig)
time.Sleep(5*time.Second)
t.Log("Done sleeping")
close(quitSig)
t.Log("closed quit signal channel")
wg.Wait()
t.Log("goroutine shutdown")
}
When I run this, I get the following
=== RUN TestWaitGroup
main.go:18: waiting for quit channel signal...
main.go:23: Done sleeping
main.go:25: closed quit signal channel
main.go:20: signal received
main.go:14: Done...
main.go:16: Done!
Where it just hangs until it timesout. If you just do defer wg.Done() the same behaviour is observed. I'm running go1.18. Is this a bug or am I using not using WaitGroups properly in this context?
Two issues:
don't copy sync.WaitGroup: from the docs:
A WaitGroup must not be copied after first use.you need a wg.Add(1) before launching your work - to pair with the wg.Done()
wg.Add(1) // <- add this
go func (wg *sync.WaitGroup ...) { // <- pointer
}(&wg, quitSig) // <- pointer to avoid WaitGroup copy