How to wait until buffered channel (semaphore) is empty?

Question

I have a slice of integers, which are manipulated concurrently:

ints := []int{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}

I\'m using a buffered channel

Answer 1

You can wait your "sub-goroutines" with the current goroutine in a for loop

semLimit := 2
sem := make(chan struct{}, semLimit)

for _, i := range ints {
  // acquire semaphore
  sem <- struct{}{}

  // start long running go routine
  go func(id int, sem chan struct{}) {
    // do something

    // release semaphore
    <- sem
  }(i, sem)
}

// wait semaphore
for i := 0; i < semLimit; i++ { 
  wg<-struct{}{} 
}

Optionnaly it is also possible to program a minimalistic "semaphored waitgroup" with the economy of import sync

semLimit := 2
// mini semaphored waitgroup 
wg := make(chan struct{}, semLimit)
// mini methods
wgAdd := func(){ wg<-struct{}{} }
wgDone := func(){ <-wg }
wgWait := func(){ for i := 0; i < semLimit; i++ { wgAdd() } }

for _, i := range ints {
  // acquire semaphore
  wgAdd()

  // start long running go routine
  go func(id int, sem chan struct{}) {
    // do something

    // release semaphore
    wgDone()
  }(i, sem)
}

// wait semaphore
wgWait()