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goroutine 使い方まとめ

Last updated at Posted at 2016-02-19

#goroutineとはなにか?
軽量スレッドである、並行処理で複数のスレッドが立てられる
「go」というシンプルなメソッドを使ってスレッドを立てる
「channel」は複数のgoroutineにメッセージを送るもの
また「select」は複数のchannelを管理するものである

mainの関数が終了しないようにgoroutineを制御する仕組みは「channel」か「sync」を使用する
以下の例はchannelを使用して複数のリクエストを並行処理で書いてある例である。

go

package main

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

func getStatus(urls []string) <-chan string {
	statusChan := make(chan string)
	for _, url := range urls {
		go func(url string) {
			res, err := http.Get(url)
			if err != nil {
				log.Fatal(err)
			}
			defer res.Body.Close()
			statusChan <- res.Status
		}(url)
	}
	return statusChan
}

func main() {
	timeout := time.After(time.Second)
	urls := []string{
		"http://example.com",
		"http://example.net",
		"http://example.org",
	}
	statusChan := getStatus(urls)

	for {
		select {
		case status := <-statusChan:
			fmt.Println(status)
		case <-timeout:
			break
		}
	}
}


syncを使って書くと以下のようになる

go
package main

import (
	"log"
	"sync"
	"net/http"
)

func getStatus(urls []string) {
	wait := new(sync.WaitGroup)
	for _, url := range urls {
		wait.Add(1)
		go func(url string) {
			res, err := http.Get(url)
			if err != nil {
				log.Fatal(err)
			}
			defer res.Body.Close()
			log.Println(url, res.Status)
			wait.Done()
		}(url)
	}
	wait.Wait()
}

func main() {
	urls := []string{
		"http://example.com",
		"http://example.net",
		"http://example.org",
	}
	getStatus(urls)
}

Do not communicate by sharing memory;instead, share memory by communicating.

の原則につきgoroutineの管理はchannelを使用してメッセージを送ってやりとりするのが望ましい。

参考URL
http://gihyo.jp/dev/feature/01/go_4beginners/0005
https://github.com/astaxie/build-web-application-with-golang/blob/master/ja/02.7.md
http://jxck.hatenablog.com/entry/20130414/1365960707

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