When using a WaitGroup to synchronize goroutines, call Add() before launching each goroutine and ensure each goroutine calls Done() exactly once. Finally, call Wait() to block until all goroutines have called Done(). Misordering Add/Done or mismatched calls will cause issues.
If you forget to Add before a goroutine or call Done more times than Add, the WaitGroup counter will go negative and panic. If you don't call Done or don't Wait properly, your program may hang. Proper usage of WaitGroup ensures no goroutines are missed and no extra signals occur, preventing panics and deadlocks.
Side-by-side examples engineers can pattern-match during review.
var wg sync.WaitGroup
go func() {
// forgot wg.Add(1)
defer wg.Done() // will panic because counter was 0
doWork()
}()
wg.Wait()var wg sync.WaitGroup
wg.Add(1)
go func() {
defer wg.Done()
doWork()
}()
wg.Wait()var wg sync.WaitGroup
go func() {
// forgot wg.Add(1)
defer wg.Done() // will panic because counter was 0
doWork()
}()
wg.Wait()var wg sync.WaitGroup
wg.Add(1)
go func() {
defer wg.Done()
doWork()
}()
wg.Wait()From the same buckets as this rule.