为什么从同一浏览器调用时 go mux 会阻塞 time.sleep？

Question

Here is my code:

package main

import (
    "fmt"
    "log"
    "net/http"
    "time"
)

func gotest(w http.ResponseWriter, req *http.Request) {
    log.Printf("starting ... Go Test()")
    for i := 0; i < 10; i++ {
        time.Sleep(2 * time.Second)
        log.Printf("Go Test %s", i)
        fmt.Fprintf(w, "Go Test %s", i)
    }
}

func main() {
    http.HandleFunc("/gotest", gotest)
    http.ListenAndServe(":3016", nil)
}

Running http://localhost:3016/gotest multiple windows using the same browser results in the gotest function running serial (not concurrent)

2020/02/22 01:24:26 starting ... Go Test()
2020/02/22 01:24:28 Go Test %!s(int=0)
2020/02/22 01:24:30 Go Test %!s(int=1)
2020/02/22 01:24:32 Go Test %!s(int=2)
2020/02/22 01:24:34 Go Test %!s(int=3)
2020/02/22 01:24:36 Go Test %!s(int=4)
2020/02/22 01:24:38 Go Test %!s(int=5)
2020/02/22 01:24:40 Go Test %!s(int=6)
2020/02/22 01:24:42 Go Test %!s(int=7)
2020/02/22 01:24:44 Go Test %!s(int=8)
2020/02/22 01:24:46 Go Test %!s(int=9)
2020/02/22 01:24:46 starting ... Go Test()
2020/02/22 01:24:48 Go Test %!s(int=0)
2020/02/22 01:24:50 Go Test %!s(int=1)
2020/02/22 01:24:52 Go Test %!s(int=2)
...

However, running http://localhost:3016/gotest in different browsers or via curl on the command line will result in concurrent execution:

2020/02/22 01:28:55 starting ... Go Test()
2020/02/22 01:28:57 Go Test %!s(int=0)
2020/02/22 01:28:58 starting ... Go Test()
2020/02/22 01:28:59 Go Test %!s(int=1)
2020/02/22 01:29:00 Go Test %!s(int=0)
2020/02/22 01:29:01 Go Test %!s(int=2)
2020/02/22 01:29:02 Go Test %!s(int=1)
2020/02/22 01:29:03 Go Test %!s(int=3)
2020/02/22 01:29:04 Go Test %!s(int=2)
2020/02/22 01:29:05 Go Test %!s(int=4)
...

Why would it matter if the url is called from different windows or tabs of the same browser vs called from different browsers?

Answer 1

this is indeed a browser issue. Changing the url to include something unique will get the browser to stop "blocking" itself.

func gotest(w http.ResponseWriter, req *http.Request) {
    log.Printf("starting ... Go Test()")
    key := req.URL.Query()["key"]
    for i := 0; i < 10; i++ {
        time.Sleep(2 * time.Second)
        log.Printf("Go Test %s %s", key, i)
        fmt.Fprintf(w, "Go Test %s %s", key, i)
    }
}

and running:

http://localhost:3016/gotest?key=A
http://localhost:3016/gotest?key=B

will result in concurrency:

2020/02/22 09:09:17 starting ... Go Test()
2020/02/22 09:09:19 Go Test [A] %!s(int=0)
2020/02/22 09:09:21 Go Test [A] %!s(int=1)
2020/02/22 09:09:22 starting ... Go Test()
2020/02/22 09:09:23 Go Test [A] %!s(int=2)
2020/02/22 09:09:24 Go Test [B] %!s(int=0)
2020/02/22 09:09:25 Go Test [A] %!s(int=3)
2020/02/22 09:09:26 Go Test [B] %!s(int=1)

This seems to be a pretty standard behavior since both Google Chrome and Firefox both do this.