osx - Different behavior in go1.5beta2 on MacOS and Linux -

the example taken "a tour of go": https://tour.golang.org/concurrency/1

obviously, program output should have 10 rows: 5 "hello" , 5 "world".

but have on:

• linux - 9 rows
• macos - 10 rows

linux output (9 rows):

$ go run 1.go  hello world hello world hello world world hello hello 

macos x output (10 rows):

$ go run 1.go  hello world world hello hello world hello world hello world 

can explain - why?

linux uname -a:

linux desktop 3.16.0-4-amd64 #1 smp debian 3.16.7-ckt11-1 (2015-05-24) x86_64 gnu/linux 

macos x uname -a:

darwin 14.5.0 darwin kernel version 14.5.0: thu jul  9 22:56:16 pdt 2015; root:xnu-2782.40.6~1/release_x86_64 x86_64 

source code tour:

package main  import (     "fmt"     "time" )  func say(s string) {     := 0; < 5; i++ {         time.sleep(1000 * time.millisecond)         fmt.println(s)     } }  func main() {     go say("world")     say("hello") } 

from the specification:

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

so there no guarantee goroutine printing "world" have time complete before program exits.

i suspect if run program enough times, see both 9-line , 10-line outputs on both platforms. setting gomaxprocs environment variable 2 might in triggering problem.

you can fix making main goroutine explicitly wait completion of other goroutine. instance, using channel:

func say(s string, done chan<- bool) {     := 0; < 5; i++ {         time.sleep(1000 * time.millisecond)         fmt.println(s)     }     done <- true }  func main() {     c := make(chan bool, 2)     go say("world", c)     say("hello", c)     <-c     <-c } 

i've added buffer channel say function can send value without blocking (primarily "hello" invocation returns). wait receive 2 values channel make sure both invocations have completed.

for more complex programs, sync.waitgroup type can provide more convenient way wait on multiple goroutines.