the program

foo.go

package main

import (
	"runtime/causalprof"
	"net/http"
	"bufio"
	"os"
	"math/rand"
	"fmt"
	"sync/atomic"
)

func main() {
	http.HandleFunc("/", randomHandler)
	go http.ListenAndServe(":9090", nil)
	select{}
	causalprof.Stop()
}

var reqcount int64

func randomHandler(w http.ResponseWriter, req *http.Request) {
	rq := atomic.AddInt64(&reqcount, 1)
	if rq == 50000 {
		causalprof.Start(os.Stdout)
	}
	p := causalprof.StartProgress()
	buffered := bufio.NewWriter(w)
	w.Header().Set("Content-Length", "20000")
	for i := 0; i < 10000; i++ {
		fmt.Fprintln(buffered, rand.Int63n(10))
	}
	buffered.Flush()
	p.Stop()
}