Why does fmt.Println inside a goroutine not print a line?

Question

I have the following code: package main import "net" import "fmt" import "bufio" func main() { conn, _ := net.Dial("tcp", "irc.freenode.net:6667") reader := bufio.NewReader(conn) go func() { str, err := reader.ReadString('
') if err != nil { // handle it fmt.Println(err) } fmt.Println(str) }() } If I don't have the code that reads from the buffer in a goroutine, it outputs a message like this, which is what I expect to happen: :zelazny.freenode.net NOTICE * :*** Looking up your hostname... However, having it inside a goroutine prints nothing. Can someone explain why that is?

Gopher · Accepted Answer

Your program will exit when the main() function finishes. This is likely to happen before your goroutine has time to run and print its output. One option would be to have the main goroutine block reading from a channel, and have the goroutine write to the channel when it has completed its work. package main import ( "bufio" "fmt" "net" ) func main() { conn, _ := net.Dial("tcp", "irc.freenode.net:6667") reader := bufio.NewReader(conn) ch := make(chan byte, 1) go func() { str, err := reader.ReadString('
') if err != nil { // handle it fmt.Println(err) } fmt.Println(str) ch <- 1 }() <-ch } https://play.golang.org/p/R8jVaN_Ho7S Another common way to "wait for a goroutines end", is using WaitGroup:http://golang.org/pkg/sync/#WaitGroup. You can usewaitGroup.Add(1) for each started goroutine, then usewaitGroup.Done() in each goroutine after it finishes. package main import ( "bufio" "fmt" "net" "sync" ) func main() { conn, _ := net.Dial("tcp", "irc.freenode.net:6667") reader := bufio.NewReader(conn) var wg sync.WaitGroup wg.Add(1) go func() { defer wg.Done() str, err := reader.ReadString('
') if err != nil { // handle it fmt.Println(err) } fmt.Println(str) }() wg.Wait() } https://play.golang.org/p/iFe1KvMcGan In the main function you can usewaitGroup.Wait()and this will wait until waitGroup.Done()has been called for each added goroutine.

Go Language

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