相同的Golang代码不同的输出，为什么？

Question

I'm trying to execute an example from golang.org : http://tour.golang.org/#63

• I Have Changed The Code To Test What Exactly Gosched does.*

You could see the output there is:

hello
hello
hello
hello
hello

But when i copy those code to my Mac OS X 10.8(Go version 1.0.3), the output has changed: xxxxxx$ go version go version go1.0.3 xxxxxx$ go run goroutine.go hello world hello world hello world hello world hello world

According to this answer, i should use runtime.GoSched, but in fact i needn't.So i believe something goes wrong.

Please help me with this, many thanks.

Answer 1

The issue here is you have two different implementations.

Locally, your code yields to the scheduler each time fmt.Println is called. Println does a write to stdout which does a syscall. All syscalls yield the same way runtime.Gosched does.

play.golang.org is a black box. We don't actually know how it works. However, from the example you gave, it appears play does not do a syscall when fmt.Println is called. This makes sense. They probably replaced os.Stdout with a buffer to hold what is printed.