I think there is a race on the WaitGroup. Add all of them before the loop.
It might not matter for what you are seeing but anyway.
What happens with an unbuffered channel?
On Fri, Nov 11, 2016, 07:08 <mspauldin...@gmail.com> wrote:
> Hello,
>
> I've written a small program to demonstrate what I am seeing. If I use a
> channel as a semaphore and set the size of the channel to 1, I would expect
> that the executions of my handle function below would all be executed in
> order, but it's not. For some reason the last item in the list is always
> handled first, and then the remaining items are handled in order. Does
> anyone know why I see this behavior?
>
> Program:
>
> package main
>
> import (
> "fmt"
> "sync"
> "time"
> )
>
> var wg sync.WaitGroup
> var sem chan int
>
> func handle(i int) {
> defer wg.Done()
> fmt.Println("waiting: ", i)
> sem <- 1
> fmt.Println("processing: ", i)
> time.Sleep(1 * time.Second)
> <-sem
> }
>
> func main() {
> sem = make(chan int, 1)
> nums := []int{1, 2, 3, 4}
>
> for _, i := range nums {
> wg.Add(1)
> go handle(i)
> }
> wg.Wait()
> }
>
> Output:
>
> waiting: 4
> processing: 4
> waiting: 1
> waiting: 2
> waiting: 3
> processing: 1
> processing: 2
> processing: 3
>
>
>
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