转到：与goroutine混淆

Question

Go experts, please someone explain the behavior of this code. why does it output Let's GoGoGo instead of the first value assigned to msg. I know this has something to do with goroutine. If someone versed with Go could explain it to me concretely I would appreciate it. Here is the playground.

package main

import (
  "fmt"
  "time"
)

// try to run: go run -race
func main() {
   msg := "Let's Go"
   go func() {
    // Print: "Let's Go"
    fmt.Println(msg)
 }()
  msg = "Let's GoGoGo"
  time.Sleep(1 * time.Second)
}

Answer 1

The very simplest answer I can give is that consider the goroutine similar to a process. When you call go func (){...}() it tells the program "Please, start this "process" in the background while I keep executing my program". As you may know, starting a process might take some time. So while it's starting up, the main program keeps executing, outputting "Let's GoGoGo". If you put your sleep before msg = "Let's GoGoGo" you would probably(not at all guaranteed!!) see "Let's Go" printed instead.

I would recommend a book, called "Concurrency in Go" to help you understand how concurrency is done in Go.