Go Race
Go Race
当两个或多个 goroutine 尝试访问同一资源时,Go 中会出现竞争条件。当变量尝试读写资源而不考虑其他例程时,可能会发生这种情况。
竞争条件示例
package main
import (
"sync"
"time"
"math/rand"
"fmt"
)
var wait sync.WaitGroup
var count int
func increment(s string) {
for i :=0;i<10;i++ {
x := count
x++;
time.Sleep(time.Duration(rand.Intn(4))*time.Millisecond)
count = x;
fmt.Println(s, i,"Count: ",count)
}
wait.Done()
}
func main(){
wait.Add(2)
go increment("foo: ")
go increment("bar: ")
wait.Wait()
fmt.Println("last count value " ,count)
}
输出:
foo: 0 Count: 1
bar: 0 Count: 1
foo: 1 Count: 2
foo: 2 Count: 3
foo: 3 Count: 4
bar: 1 Count: 2
foo: 4 Count: 5
foo: 5 Count: 6
foo: 6 Count: 7
bar: 2 Count: 3
bar: 3 Count: 4
bar: 4 Count: 5
foo: 7 Count: 8
foo: 8 Count: 9
bar: 5 Count: 6
bar: 6 Count: 7
foo: 9 Count: 10
bar: 7 Count: 8
bar: 8 Count: 9
bar: 9 Count: 10
last count value 10
如上例所示,count资源被2个goroutine访问。每个例程迭代 10 次。在这种情况下,计数变量最终应该是 20。但事实并非如此,因为它模拟了竞争条件。