为什么我的for循环仅在我放慢速度时才起作用？

Question

This code prints 0, but if I insert time.Sleep(0) into the updater loop, it prints >1

var Nonce int = 0

func Updater(){
    for{
        Nonce += 1
    }
}

func main(){
    go Updater()
    time.Sleep(time.Second)
    fmt.Printf("%d
",Nonce)
}

Answer 1

Your main function spins up a goroutine to run Updater and then immediately exits. Without the sleep, Updater doesn't have time to start and do its thing. This code is racy - it will sometimes work as you expect and sometimes won't. You have to synchronize the Updater goroutine with main somehow, using a channel or a wait group for example.

Moreover, you're updating the Nonce global in one goroutine and reading it in another - this is a data race. You'll need to synchronize access to this var with a mutex.

---

Here's a more correct variant of your code, though it's still rather non-sensical (why do you need a goroutine to run the busy loop?)

package main

import (
    "fmt"
    "sync"
)

var Nonce int = 0

func Updater(wg *sync.WaitGroup) {
    defer wg.Done()
    for i := 0; i < 1000; i++ {
        Nonce += 1
    }
}

func main() {
    var wg sync.WaitGroup
    wg.Add(1)
    go Updater(&wg)
    wg.Wait()
    fmt.Printf("%d
", Nonce)
}

Here we use a WaitGroup for the Updater to signal "I'm done" to the main goroutine, which only then checks the value of Nonce. This program should print "1000" every time