Waiting goroutines in go with sync.WaitGroup

When we need to invoke some functions asynchronousely, we can use goroutine to achive the the goal.

// first
go func () {
  // do something here
}()

// second
go func () {
  // do something here
}()

// third
go func () {
  // do something here
}()

// other codes here will immediately executed

All the functions above will be invoked almost at the same time, no waiting any previous function to complete.

But how if we want to wait all of it berfore going to other next codes?

There’s why sync.WaitGroup exists for!

We can use sync.WaitGroup to wait some group of goroutines to complete first before we move to next code lines.

import (
  "sync"
)

var wg sync.WaitGroup
wg.Add(3)

// first
go func () {
  defer wg.Done()
  // do something here
}()

// second
go func () {
  defer wg.Done()
  // do something here
}()

// third
go func () {
  defer wg.Done()
  // do something here
}()

wg.Wait()

// other lines of code...

wg.Wait() waits the 3 goroutines to be done, then move to the next lines.