Goroutine の並列性(Parallelism)について検証する

goroutine.go

package main

import (
	"crypto/sha256"
	"fmt"
	"io"
	"log"
	"os"
	"runtime"
	"runtime/trace"
)

func main() {
	f, err := os.Create("runtime.trace")
	if err != nil {
		fmt.Println(err)
	}
	trace.Start(f)
	defer trace.Stop()

	byForLoop()
	byGoroutine(1)
	byGoroutine(4)
	byGoroutine(runtime.NumCPU())
}

func getHash() string {
	f, err := os.Open("./golang/debian-10.8.0-amd64-netinst.iso")
	if err != nil {
		log.Fatal(err)
	}
	defer f.Close()
	h := sha256.New()
	if _, err := io.Copy(h, f); err != nil {
		log.Fatal(err)
	}
	hash := fmt.Sprintf("%x", h.Sum(nil))
	return hash
}

func getHashByChannel(c chan string) {
	c <- getHash()
}

func byForLoop() {
	loopCount := 30
	for i := 0; i < loopCount; i++ {
		hash := getHash()
		fmt.Println(hash)
	}
}

func byGoroutine(numberOfCPU int) {
	runtime.GOMAXPROCS(numberOfCPU)
	c := make(chan string)
	loopCount := 30
	for i := 0; i < loopCount; i++ {
		go getHashByChannel(c)
	}
	for i := 0; i < loopCount; i++ {
		hash := <-c
		fmt.Println(hash)
	}
}