Wait for the termination of n goroutines

Question

I need to start a huge amount of goroutines and wait for their termination. The intuitive way seems to use a channel to wait till all of them are finished :

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Answer 1

@tjameson did a great job explaining how to use WaitGroup, how to pass a reference to your WaitGroup object to your function. The one change I would make to his example is leverage defer when you are Done. I think this defer ws.Done() should be the first statement in your function.

I like WaitGroup's simplicity. However, I do not like that we need to pass the reference to the goroutine because that would mean that the concurrency logic would be mixed with your business logic.

So I came up with this generic function to solve this problem for me:

// Parallelize parallelizes the function calls
func Parallelize(functions ...func()) {
    var waitGroup sync.WaitGroup
    waitGroup.Add(len(functions))

    defer waitGroup.Wait()

    for _, function := range functions {
        go func(copy func()) {
            defer waitGroup.Done()
            copy()
        }(function)
    }
}

So your example could be solved this way:

type Object struct {
    //data
}

func (obj *Object) Update() {
    //update data
    time.Sleep(time.Second)
    fmt.Println("Update done")
    return
}

func main() {
    functions := []func(){}
    list := make([]Object, 5)
    for _, object := range list {
        function := func(obj Object){ object.Update() }(object)
        functions = append(functions, function)
    }

    Parallelize(functions...)        

    fmt.Println("Group done")
}

If you would like to use it, you can find it here https://github.com/shomali11/util