[Go] p3 multi-distributor-consumer

package main
//2020  Aion Algos#9218 http://discord.futuregadgetlab.net
import (
  "fmt"
  "time"
  "sync"
  "container/list"
)

type Stack struct {
  stack *list.List
}

func (s *Stack) Push(value int) {
  s.stack.PushFront(value)
}

func (s *Stack) Pop() (int, error) {
  if (s.stack.Len() > 0) {
    ele := s.stack.Front()
    s.stack.Remove(ele)
    return ele.Value.(int),nil
  }
  return 0,fmt.Errorf("Error: Nothing to Pop")
}

func (s *Stack) Empty() bool {
    return s.stack.Len() == 0
}

func main() {
  fmt.Println("Multi-Distributor-Consumer example starting.")
  distributors := 5
  consumers := 20
  buffer := 1

  var stack_mutex sync.Mutex
  stack := &Stack { stack: list.New() }
  for i := 0; i < 256; i++ {
    stack.Push(i)
  }

  queue := make(chan int, buffer)

  var dwg sync.WaitGroup
  dwg.Add(distributors)
  for i := 0; i < distributors; i++ {
    go distributor(i, &dwg, &stack_mutex, stack, queue)
  }

  var cwg sync.WaitGroup
  cwg.Add(consumers)
  for i := 0; i < consumers; i++ {
    go consumer(i, &cwg, queue)
  }

  dwg.Wait()
  close(queue)
  cwg.Wait()
  if (stack.Empty() != true) {
    fmt.Println("Something went wrong! Items are still on the stack!")
  } else { fmt.Println("Multi-Distributor-Consumer example complete.") }
}

func consumer(id int, wg *sync.WaitGroup, queue <-chan int) {
  fmt.Println("Consumer", id, "started.")
  defer wg.Done()
  for q := range queue {
    fmt.Println("Consumer", id, "recieved:", q)
    time.Sleep(time.Millisecond * 200)
  }
  fmt.Println("Consumer", id, "done.")
}

func distributor(id int, wg *sync.WaitGroup, sm *sync.Mutex, s *Stack, queue chan<- int) {
  defer wg.Done()
  fmt.Println("Distributor", id, "started.")
  for {
    if s.Empty() {
      break;
    }
    // enter critical section
    sm.Lock()
    i,e := s.Pop()
    sm.Unlock()
    // leave critical section
    if e != nil {
      fmt.Println("Distributor", id, e)
      break;
    }
    queue<- i
    fmt.Println("Distributor", id, "produced:", i)
  }
  fmt.Println("Distributor", id, "done.")
}