Waitgroups: What they are, how to use them and what changed with Go 1.25
42 comments
·August 23, 2025tombert
arccy
CountDownLatch looks like it can only count down? the go one you can add/remove at will
layer8
Phaser [0] would be the more flexible equivalent in Java.
[0] https://docs.oracle.com/javase/7/docs/api/java/util/concurre...
tombert
You are right; it looks like a Phaser is a bit more analogous: https://docs.oracle.com/javase/8/docs/api/java/util/concurre...
xh-dude
Pretty much. It’s a counting semaphore underneath.
stefanos82
Personally I wished they had it backported to previous versions too, because it's rather convenient!
What is quite sad is that we cannot add it ourselves as it's so simple of what they have done:
func (wg *WaitGroup) Go(f func()) {
wg.Add(1)
go func() {
defer wg.Done()
f()
}()
}evanelias
You can just use golang.org/x/sync/errgroup instead, which has always provided this style of use.
errgroup also has other niceties like error propagation, context cancellation, and concurrency limiting.
Cyph0n
Context cancellation is not always desirable. I personally have been bitten multiple times by the default behavior of errgroup.
CamouflagedKiwi
You have to explicitly propagate the group's context if you want it to cancel. You can just not do that if you don't want - there certainly are cases for that.
porridgeraisin
errgroup cancels the whole task if even one subtask fails however. That is not desirable always.
Groxx
It does not, which is easy to verify from the source. Every func passed in is always run (with the exception of TryGo which is explicitly "maybe").
At best, using the optional, higher-effort errgroup.WithContext will cancel the context but still run all of your funcs. If you don't want that for one of the funcs, or some component of them, just don't use the context.
evanelias
If the context cancellation is undesirable, you just choose not to use WithContext, as the sibling comment mentions.
You could also just make your subtask function return nil always, if you just want to get the automatic bookkeeping call pattern (like WaitGroup.Go from Golang 1.25), plus optional concurrency limiting.
Also note, even if a subtask function returns an error, the errgroup Wait blocking semantics are identical to those of a WaitGroup. Wait will return the first error when it returns, but it doesn't unblock early on first error.
CamouflagedKiwi
They basically don't backport anything for Go, but the quid pro quo for that is that the backwards compatibility is pretty strong so upgrades should be safe. I have seen one serious issue from it, but still it's the language I'm the most confident to do an upgrade and expect things to Just Work afterwards.
cedws
You can wrap WaitGroup if you really want to.
stefanos82
Can you provide an example please?
listeria
something like this would do it:
package main
import (
"sync"
"time"
)
type WaitGroup struct {
sync.WaitGroup
}
func (wg *WaitGroup) Go(fn func()) {
wg.Add(1)
go func() {
defer wg.Done()
fn()
}()
}
func main() {
var wg WaitGroup
wg.Go(func() { time.Sleep(1 * time.Second) })
wg.Wait()
}danenania
I like WaitGroup as a concept, but I often end up using a channel instead for clearer error handling. Something like:
errCh := make(chan error)
for _, url := range urls {
go func(url string){
errCh <- http.Get(url)
}(url)
}
for range urls {
err := <-errCh
if err != nil {
// handle error
}
}
c0balt
You would probably benefit from errgroup, https://pkg.go.dev/golang.org/x/sync/errgroup
But channels already do the waiting part for you.
danenania
Thanks! looking into errgroup
javier2
How you handle err here? If you return, the go routines will leak
danenania
Ah, good point—should be using a buffered channel to avoid that:
errCh := make(chan error, len(urls))unsnap_biceps
buffered channels won't help here. That's just how many results can be buffered before the remaining results can be added to the channel. It doesn't wait until all of them are done before returning a result to the consumer.
porridgeraisin
Love this. Majority of concurrency in a usual web service is implemented using waitgroups IME (see below) This will greatly simplify it.
var wg sync.WaitGroup
wg.Add(1)
go func(){
callService1(inputs, outParameter)
wg.Done()
}
// Repeat for services 2 through N
wg.Wait()
// Combine all outputs
type WaitGroup struct { sync.WaitGroup }
func (wg *WaitGroup) Go(fn func()) {
wg.Add(1)
go func() {
fn()
wg.Done()
}()
}
nikolayasdf123
> wg := sync.WaitGroup{}
just `var wg sync.WaitGroup`, it is cleaner this way
fozdenn
doesn't this point to a bigger problem that there are two ways of doing the same thing?
unsnap_biceps
multiple ways of doing something isn't inherently bad.
For example, if you want to set a variable to the number of seconds in seven hours, you could just set the variable to 25200, or you could set it to 60 * 60 * 7. The expanded version might be clearer in the code context, but in the end they do exactly the same thing.
pests
Your math equation turned the asterisks into italics.
nikolayasdf123
no. it is different thing. container-agnostic zero value vs struct init.
mr90210
Oh you are one of those. The nit picker. This is not at a PR review mate.
nikolayasdf123
"one of those", name calling, telling me what to say,
cool it down a little. touch some grass. and hopefully you will see beauty in Go zero-values :P
dwb
Why?
nikolayasdf123
zero value. container-agnostic initialization. say your type is not struct anymore, you would not have to change the way you intialize it. what you care here is zero value, and let the type figure out that it is zero and use methods appropriately. and it is just more clean this way
here is google guideline: https://google.github.io/styleguide/go/best-practices#declar...
dwb
That is a much better argument than saying it is "more clean", which doesn't mean anything. I don't necessarily agree, because I don't think zero values are a good feature of the language, and even if they were this is a completely trivial case. But at least I don't have to work out what "cleanliness" is.
a-poor
This means you can't pass variables in as function arguments. Even the example in the official go docs doesn't handle the scope correctly:
func main() {
var wg sync.WaitGroup
var urls = []string{
"http://www.golang.org/",
"http://www.google.com/",
"http://www.example.com/",
}
for _, url := range urls {
// Launch a goroutine to fetch the URL.
wg.Go(func() {
// Fetch the URL.
http.Get(url)
})
}
// Wait for all HTTP fetches to complete.
wg.Wait()
}
You need to use this pattern instead:
for _, url := range urls {
url := url
// ...jeremyloy_wt
This isn’t necessary anymore as of Go 1.22
9rx
> This means you can't pass variables in as function arguments.
Well, you could...
for _, url := range urls {
wg.Go(func(u string) func() {
return func() {
http.Get(u)
}
}(url))
}
Why? Seems rather redundant. It is not like WaitGroup.Go exists in earlier versions.
Forgive a bit of ignorance, it's been a bit since I've touched Go, but this looks awfully similar to a Java CountdownLatch [1]. Is this just a glorified Go port of that or am I missing something vital here?
[1] https://docs.oracle.com/javase/8/docs/api/java/util/concurre...