go - What's wrong with this golang code? -

while sayhello() executes expected, goroutine prints nothing.

package main  import "fmt"  func sayhello() {     := 0; < 10 ; i++ {         fmt.print(i, " ")     } }  func main() {     sayhello()     go sayhello() } 

when main() function ends, program ends well. not wait other goroutines finish.

quoting go language specification: program execution:

program execution begins initializing main package , invoking function main. when function invocation returns, program exits. not wait other (non-main) goroutines complete.

see this answer more details.

you have tell main() function wait sayhello() function started goroutine complete. can synchronize them channels example:

func sayhello(done chan int) {     := 0; < 10; i++ {         fmt.print(i, " ")     }     if done != nil {         done <- 0 // signal we're done     } }  func main() {     sayhello(nil) // passing nil: don't want notification here     done := make(chan int)     go sayhello(done)     <-done // wait until done signal arrives } 

another alternative signal completion closing channel:

func sayhello(done chan struct{}) {     := 0; < 10; i++ {         fmt.print(i, " ")     }     if done != nil {         close(done) // signal we're done     } }  func main() {     sayhello(nil) // passing nil: don't want notification here     done := make(chan struct{})     go sayhello(done)     <-done // receive closed channel returns 0 value } 

notes:

according edits/comments: if want 2 running sayhello() functions print "mixed" numbers randomly: have no guarantee observe such behaviour. again, see aforementioned answer more details. go memory model guarantees events happen before other events, have no guarantee how 2 concurrent goroutines executed.

you might experiment it, know result not deterministic. first have enable multiple active goroutines executed with:

runtime.gomaxprocs(2) 

and second have first start sayhello() goroutine because current code first executes sayhello() in main goroutine , once finished starts other one:

runtime.gomaxprocs(2) done := make(chan struct{}) go sayhello(done) // first start goroutine sayhello(nil) // , call sayhello() in main goroutine <-done // wait completion