英文:
Is this a race condition in go
问题
func main() {m := map[string]int{"foo": 42,"bar": 1337,}go func() {time.Sleep(1 * time.Second)tmp := map[string]int{"foo": 44,"bar": 1339,}m = tmp}()for {val := m["foo"]fmt.Println(val)}}
我在许多包中看到了这段代码。
为什么这不被视为竞态条件？
go run -race . 没有报错。
英文:
func main() {m := map[string]int{"foo": 42,"bar": 1337,}go func() {time.Sleep(1 * time.Second)tmp := map[string]int{"foo": 44,"bar": 1339,}m = tmp}()for {val := m["foo"]fmt.Println(val)}}
I saw this in many packages.
Why this is not considered as a race condition?
go run -race . giving no error.
答案1
得分: 3
如@Volker所指出的，这是一个数据竞争。由于只有一个写入操作，很难检测到。这里是一个修改后的示例，可以更容易地触发数据竞争错误：
package mainimport ("fmt""time")func main() {m := map[string]int{"foo": 42,"bar": 1337,}done := make(chan any)go func() {for i := 0; i < 100; i++ {time.Sleep(time.Microsecond)tmp := map[string]int{"foo": 44,"bar": 1339,}m = tmp}close(done)}()for {select {case <-done:returndefault:val := m["foo"]fmt.Println(val)}}}
英文:
As pointed out by @Volker, this is a data race. And since there is only one write, it's hard to be detected. Here is a modified demo to make it easy to trigger the data race error:
package mainimport ("fmt""time")func main() {m := map[string]int{"foo": 42,"bar": 1337,}done := make(chan any)go func() {for i := 0; i < 100; i++ {time.Sleep(time.Microsecond)tmp := map[string]int{"foo": 44,"bar": 1339,}m = tmp}close(done)}()for {select {case <-done:returndefault:val := m["foo"]fmt.Println(val)}}}
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