Go言語のゴルーチン・チャネルの使い方メモ

はじめに

何回かGo言語で処理を作ったことがあったけど、Go言語で並行処理を一切書いたことがなかったので、勉強がてら簡単な処理を書いてみることにした。

参考サイト

qiita.com

環境

• Go: 1.13.8 linux/amd64
• Ubuntu 20.04.2 LTS

並行処理しない

とりあえず並行処理していないコードを書いた

package sample

import (
    "fmt"
    "log"
    "time"
)

func NotUseGoRoutine() {
    log.Println("---------- Start Sample 01 ----------")
    process("first ", 10)
    process("second", 10)
    process("third ", 10)
    log.Println("----------  End Sample 01  ----------")
}

func process(name string, loopCount int) {
    commonLoopMessage(name, loopCount)
}

func commonLoopMessage(name string, loopCount int)  {
    for count := 1; count <= loopCount; count++ {
        time.Sleep(time.Second / 10)
        fmt.Printf("name: %s, loopCount: %d\n", name, count)
    }
}

出力

2021/05/28 06:49:38 ---------- Start Sample 01 ----------
name: first , loopCount: 1
name: first , loopCount: 2
name: first , loopCount: 3
name: first , loopCount: 4
name: first , loopCount: 5
name: first , loopCount: 6
name: first , loopCount: 7
name: first , loopCount: 8
name: first , loopCount: 9
name: first , loopCount: 10
name: second, loopCount: 1
name: second, loopCount: 2
name: second, loopCount: 3
name: second, loopCount: 4
name: second, loopCount: 5
name: second, loopCount: 6
name: second, loopCount: 7
name: second, loopCount: 8
name: second, loopCount: 9
name: second, loopCount: 10
name: third , loopCount: 1
name: third , loopCount: 2
name: third , loopCount: 3
name: third , loopCount: 4
name: third , loopCount: 5
name: third , loopCount: 6
name: third , loopCount: 7
name: third , loopCount: 8
name: third , loopCount: 9
name: third , loopCount: 10
2021/05/28 06:49:41 ----------  End Sample 01  ----------

並行処理する

さっきのコードを並行処理するように書き換える

並行処理が終わる前に関数を抜けないように、チャネルを使い、並行処理が終わるまでブロックする

参考サイトを見つつ修正

func UseGoRoutine01() {
    log.Println("---------- Start Sample 02 ----------")
    ch1 := make(chan bool)
    ch2 := make(chan bool)
    ch3 := make(chan bool)

    go processWithCh01(ch1, "first ", 10)
    go processWithCh01(ch2, "second", 10)
    go processWithCh01(ch3, "third ", 10)

    <- ch1
    fmt.Println("Receive ch1 message")
    <- ch2
    fmt.Println("Receive ch2 message")
    <- ch3
    fmt.Println("Receive ch3 message")

    log.Println("----------  End Sample 02  ----------")
}

func processWithCh01(ch chan bool, name string, loopCount int) {
    commonLoopMessage(name, loopCount)
    ch <- true
}

出力

2021/05/28 06:49:41 ---------- Start Sample 02 ----------
name: second, loopCount: 1
name: third , loopCount: 1
name: first , loopCount: 1
name: second, loopCount: 2
name: third , loopCount: 2
name: first , loopCount: 2
name: third , loopCount: 3
name: second, loopCount: 3
name: first , loopCount: 3
name: third , loopCount: 4
name: first , loopCount: 4
name: second, loopCount: 4
name: second, loopCount: 5
name: third , loopCount: 5
name: first , loopCount: 5
name: first , loopCount: 6
name: second, loopCount: 6
name: third , loopCount: 6
name: third , loopCount: 7
name: second, loopCount: 7
name: first , loopCount: 7
name: first , loopCount: 8
name: third , loopCount: 8
name: second, loopCount: 8
name: third , loopCount: 9
name: second, loopCount: 9
name: first , loopCount: 9
name: first , loopCount: 10
Receive ch1 message
name: second, loopCount: 10
Receive ch2 message
name: third , loopCount: 10
Receive ch3 message
2021/05/28 06:49:42 ----------  End Sample 02  ----------

ちょっと修正

チャネルは破棄できるらしい。（チャネルの戻り値を無視することではなく、チャネルをメモリから破棄的な意味）

チャネル破棄について調べると以下のサイトを発見

hori-ryota.com

チャネルを使う場合、以下の注意点があるらしい（他にもあるだろうけど）

• 破棄したチャネルにイベントを送ると panic する
• チャネルを多重に破棄すると panic する
• 受信が先にいなくなるとブロックし続ける

また「処理が終了したこと」のみを通知する場合、チャネルに使用する型は「struct{}」で良いらしい

「struct{}」のサイズが「0」なので、通知のデータサイズが無いことを明示できる

qiita.com

func UseGoRoutine02() {
    log.Println("---------- Start Sample 03 ----------")
    ch1 := make(chan struct{})
    ch2 := make(chan struct{})
    ch3 := make(chan struct{})

    go processWithCh02(ch1, "first ", 10)
    go processWithCh02(ch2, "second", 10)
    go processWithCh02(ch3, "third ", 10)

    <- ch1
    fmt.Println("Receive ch1 message")
    <- ch2
    fmt.Println("Receive ch2 message")
    <- ch3
    fmt.Println("Receive ch3 message")

    log.Println("----------  End Sample 03  ----------")
}

func processWithCh02(ch chan struct{}, name string, loopCount int) {
    commonLoopMessage(name, loopCount)
    close(ch)
}

出力

2021/05/28 06:49:42 ---------- Start Sample 03 ----------
name: second, loopCount: 1
name: first , loopCount: 1
name: third , loopCount: 1
name: second, loopCount: 2
name: first , loopCount: 2
name: third , loopCount: 2
name: third , loopCount: 3
name: second, loopCount: 3
name: first , loopCount: 3
name: first , loopCount: 4
name: third , loopCount: 4
name: second, loopCount: 4
name: second, loopCount: 5
name: first , loopCount: 5
name: third , loopCount: 5
name: third , loopCount: 6
name: second, loopCount: 6
name: first , loopCount: 6
name: first , loopCount: 7
name: third , loopCount: 7
name: second, loopCount: 7
name: second, loopCount: 8
name: first , loopCount: 8
name: third , loopCount: 8
name: third , loopCount: 9
name: first , loopCount: 9
name: second, loopCount: 9
name: third , loopCount: 10
name: second, loopCount: 10
name: first , loopCount: 10
Receive ch1 message
Receive ch2 message
Receive ch3 message
2021/05/28 06:49:43 ----------  End Sample 03  ----------