foobar.go

package main

import (
	"fmt"
	"net/http"
	_ "net/http/pprof"
	"runtime/causalprof"
	"sync"
	"math/rand"
)

func main() {
	http.HandleFunc("/", foo)
	http.ListenAndServe("localhost:8080", nil)
}

var m sync.RWMutex

func foo(rw http.ResponseWriter, req *http.Request) {
	p := causalprof.StartProgress()
	m.RLock()
	fmt.Fprintln(rw, "whatup")
	m.RUnlock()
	p.Stop()
	if rand.Intn(100) == 0 {
		m.Lock()
		ch := make(chan int, 1)
		go func() {
			bar()
			ch <- 1
		}()
		<-ch
		m.Unlock()
	}
}

func bar() {
	for i := 0; i < 100000000; i++ {}
}

// gotip run $%

results

0x47b245 /home/daniel/go/src/syscall/zsyscall_linux_amd64.go:1029
  0%	30577668ns
 30%	31514493ns	+3.06%

0x653334 /home/daniel/go/src/net/http/header.go:46
no null experiment, skip

0x434ab7 /home/daniel/go/src/runtime/proc.go:2329
  0%	30999084ns

0x44b722 /home/daniel/go/src/runtime/symtab.go:726
  0%	31455962ns

0x41e494 /home/daniel/go/src/runtime/mgcmark.go:779
no null experiment, skip

0x440384 /home/daniel/go/src/runtime/sema.go:66
  0%	31383410ns

0x65500b /home/daniel/go/src/net/http/server.go:364
no null experiment, skip

0x65db09 /home/daniel/go/src/net/http/server.go:2172
  0%	24921347ns

0x6e3162 /home/daniel/src/github.com/DanielMorsing/test/foobar.go:29
  0%	24486960ns
  5%	26024808ns	+6.28%
 10%	28369246ns	+15.9%
 15%	26537050ns	+8.37%
 20%	21538955ns	-12%
 25%	21108880ns	-13.8%
 30%	19283509ns	-21.2%
 35%	17088468ns	-30.2%
 40%	17652392ns	-27.9%
 45%	12271748ns	-49.9%
 50%	14961467ns	-38.9%
 55%	11343666ns	-53.7%
 60%	11790047ns	-51.9%
 65%	13001082ns	-46.9%
 70%	9152066ns	-62.6%
 75%	7430681ns	-69.7%
 80%	7925614ns	-67.6%
 85%	7325838ns	-70.1%
 90%	4147780ns	-83.1%
 95%	3696183ns	-84.9%
100%	54509441ns	+123%