Re: [go-nuts] go log.Println(http.ListenAndServe(...)) blocks

[Robert Engels]

Because the arguments are evaluated when the go keyword is encountered - and 
listen and serve is blocking on port 8082

> On Feb 18, 2022, at 10:38 AM, Christoph Berger  
> wrote:
> 
> 
> Hi gophers, 
> 
> I hope someone can help finding out why a particular goroutine call can block 
> the main goroutine.
> 
> In the following code, all "go" calls spawn off a goroutine and return as 
> expected, except for the last one that blocks the main goroutine. 
> 
> Is this a bug, or am I missing something subtle or even obvious (obvious to 
> all others only of course)?
> 
> package main
> 
> import (
> "log"
> "net/http"
> )
> 
> func main() {
> // all of these work as expected
> go http.ListenAndServe("localhost:8080", nil)
> go log.Println("goroutine")
> go func() {
> log.Println(http.ListenAndServe("localhost:8081", nil))
> }()
> 
> // The following line blocks the main goroutine.
> go log.Println(http.ListenAndServe("localhost:8082", nil))
> 
> log.Println("after go log.Println(http.ListenAndServe())") // never 
> prints
> select {} // remove this, and the code still never finishes
> }
> 
> All three servers eventually run (try curl localhost:8080; curl 
> localhost:8081; curl localhost:8082),
> 
> In the playground, the code even deadlocks. 
> 
> Any idea?
> 
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[go-nuts] go log.Println(http.ListenAndServe(...)) blocks

[Christoph Berger]

Hi gophers, 

I hope someone can help finding out why a particular goroutine call can 
block the main goroutine.

In the following code, all "go" calls spawn off a goroutine and return as 
expected, except for the last one that blocks the main goroutine. 

Is this a bug, or am I missing something subtle or even obvious (obvious to 
all others only of course)?

package main

import (
"log"
"net/http"
)

func main() {
// all of these work as expected
go http.ListenAndServe("localhost:8080", nil)
go log.Println("goroutine")
go func() {
log.Println(http.ListenAndServe("localhost:8081", nil))
}()

// The following line blocks the main goroutine.
go log.Println(http.ListenAndServe("localhost:8082", nil))

log.Println("after go log.Println(http.ListenAndServe())") // never 
prints
select {} // remove this, and the code still never finishes
}

All three servers eventually run (try curl localhost:8080; curl 
localhost:8081; curl localhost:8082),

In the playground , the code even 
deadlocks. 

Any idea?

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