No output from goroutine

Question

While SayHello() executes as expected, the goroutine prints nothing. package main import "fmt" func SayHello() { for i := 0; i < 10 ; i++ { fmt.Print(i, " ") } } func main() { SayHello() go SayHello() }

Gopher · Accepted Answer

When your main() function ends, your program ends as well. It does not wait for other goroutines to finish. Quoting from the Go Language Specification: Program Execution: Program execution begins by initializing the main package and then invoking the function main. When that function invocation returns, the program exits. It does not wait for other (non-main) goroutines to complete. You have to tell your main() function to wait for the SayHello() function started as a goroutine to complete. You can synchronize them with channels for example: package main import "fmt" func SayHello(done chan int) { for i := 0; i < 10; i++ { fmt.Print(i, " ") } if done != nil { done <- 0 // Signal that we're done } } func main() { SayHello(nil) // Passing nil: we don't want notification here done := make(chan int) go SayHello(done) <-done // Wait until done signal arrives } https://play.golang.org/p/hW4XxxOsfKJ 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 ( "fmt" "sync" ) func SayHello() { for i := 0; i < 10; i++ { fmt.Print(i, " ") } } func main() { SayHello() var wg sync.WaitGroup wg.Add(1) go func() { defer wg.Done() SayHello() }() wg.Wait() } https://play.golang.org/p/y6Kpcz0pOUP 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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