Some confusion of Go `net/http` under high concurrency - go

Question

Some confusion under high concurrency.
I use wrk to test Gin, there's someting uncertainty. Gin seems doesn't concurrency safe.
package main
import (
"fmt"
"sync/atomic"
"github.com/gin-gonic/gin"
)
var count int64 = 0
func Test(c *gin.Context) {
atomic.AddInt64(&count, 1)
fmt.Println(count)
c.String(200, "success")
}
func main() {
gin.SetMode(gin.DebugMode)
router := gin.New()
router.GET("test", Test)
router.Run(":8080")
}
Test shell code
wrk -t50 -c50 -d 1s http://localhost:8080/test
Gin output duplicate data
========update========
even if the print code like this.
countCopy := count
go func() {
fmt.Println(countCopy)
}()
I also use ab test it, the same problem.
========update========
The same with net/http, still has duplicate data.
package main
import (
"fmt"
"net/http"
"sync/atomic"
)
var count int64 = 0
func Test(w http.ResponseWriter, req *http.Request) {
atomic.AddInt64(&count, 1)
fmt.Println(count)
w.Write([]byte("success"))
}
func main() {
http.HandleFunc("/test", Test)
http.ListenAndServe(":8080", nil)
}
I try to use log package, which is safe from concurrent goroutines . The same.
log.Println(countCopy)

Answer 1

You have to use the returned value from atomic.AddInt64(&count, 1), as count can change before you have a chance to print it:
func Test(c *gin.Context) {
current := atomic.AddInt64(&count, 1)
fmt.Println(current)
c.String(200, "success")
}