Go中的竞争条件发生了变化

关于竞争条件的"开始行动"的样本:

var (
    counter int
    wg sync.WaitGroup
)

func main() {
    wg.Add(2)
    go incCounter(1)
    go incCounter(2)

    wg.Wait()
    fmt.Println("Final Counter:", counter)
}

func incCounter(id int) {
    defer wg.Done()

    for count := 0; count <2; count++ {
        value := counter
        //1 fmt.Println("value=",value)
        runtime.Gosched()

        value++

        counter = value
        //2 fmt.Println("counter=",counter)
    }
}

最后计数器最终应该是2,这里解释说:"每个goroutine都会覆盖另一个goroutine的工作.这发生在goroutine交换发生的时候.每个goroutine都会自己制作一个计数器变量的副本,然后进行交换当goroutine被给予时间再次执行时,计数器变量的值已经改变,但是goroutine不会更新它的副本.而是继续增加它的副本并将值设置回计数器变量,替换其他goroutine执行的工作."

我猜这是环境原因,我的机器输出4与1.10.3 + win10.我想知道自这本书发布以来发生了什么变化？如果我取消注释标记1最终计数器打印2或随机,如果我取消注释标记2.为什么？

这本书错了.关于数据竞争的要点是结果未定义.

例如,Final Counter可以是任何值.

package main

import (
    "fmt"
    "runtime"
    "sync"
)

var (
    counter int
    wg      sync.WaitGroup
)

func main() {
    wg.Add(2)
    go incCounter(1)
    go incCounter(2)

    wg.Wait()
    fmt.Println("Final Counter:", counter)
}

func incCounter(id int) {
    defer wg.Done()

    for count := 0; count <2; count++ {
        value := counter
        //1 fmt.Println("value=",value)
        runtime.Gosched()

        value++

        counter = value
        //2 fmt.Println("counter=",counter)
    }
}

输出:

$ go version
go version devel +65fa2b615b Fri Aug 3 23:35:53 2018 +0000 linux/amd64
$ go run racer.go
Final Counter: 4
$ go run racer.go
Final Counter: 2
$ go run racer.go
Final Counter: 2
$ go run racer.go
Final Counter: 2
$ go run racer.go
Final Counter: 2
$ go run racer.go
Final Counter: 4
$ go run racer.go
Final Counter: 2
$ go run racer.go
Final Counter: 4
$ go run -race racer.go
==================
WARNING: DATA RACE
Read at 0x0000005e4600 by goroutine 7:
  main.incCounter()
      /home/peter/gopath/src/racer.go:27 +0x6f

Previous write at 0x0000005e4600 by goroutine 6:
  main.incCounter()
      /home/peter/gopath/src/racer.go:33 +0x90

Goroutine 7 (running) created at:
  main.main()
      /home/peter/gopath/src/racer.go:17 +0x89

Goroutine 6 (finished) created at:
  main.main()
      /home/peter/gopath/src/racer.go:16 +0x68
==================
Final Counter: 4
Found 1 data race(s)
exit status 66
$