[英]race conditions change in Go
《 Go in action》關於比賽條件的樣本:
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)
}
}
據說最終計數器的末尾應為2,解釋如下:“每個goroutine都會覆蓋另一個工作。這在goroutine交換發生時發生。每個goroutine制作自己的counter變量副本然后被交換當另一個goroutine再次執行時,counter變量的值已更改,但goroutine不會更新其副本,而是繼續增加其副本並將其值設置為計數器變量,替換其他goroutine執行的工作。”
我想這是環境原因,我的機器輸出4為1.10.3 + win10。 我想知道自本書發行以來發生了什么變化? 如果我取消注釋1,則最終計數器將打印2;如果我取消注釋2,則將隨機打印2。為什么?
這本書是錯的。 關於數據爭用的要點是結果不確定。
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)
}
}
輸出:
$ 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
$
聲明:本站的技術帖子網頁,遵循CC BY-SA 4.0協議,如果您需要轉載,請注明本站網址或者原文地址。任何問題請咨詢:yoyou2525@163.com.