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@kosuke-oya(kosuke oya)

【Go言語】for文とgoroutineとsync.WaitGroupの使い方

Last updated at Posted at 2023-04-11

for文とgoroutineとsync.WaitGroupの使い方

func A : funcAスタート　→　1秒待機　→ funcA終了
func B : funcBスタート　→　3秒待機　→ funcB終了

大前提

funcAとfuncBをfor文で3回実行する

これらの順序制御するテンプレを作成する
何も使わない基本コードは↓

package main

import (
	"fmt"
	"time"
)

func main() {
	//時間経過線を入れるためのコード
	go func() {
		for {
			time.Sleep(300 * time.Millisecond) //わかりやすいように0.3秒ごとに線を表示
			fmt.Println("--------------0.3秒経過-----------------")
		}
	}()
	//時間経過線を入れるためのコード終了
	for i := 0; i < 3; i++ {
		func() { //funcA
			fmt.Println("funcA started")
			time.Sleep(1000 * time.Millisecond)
			fmt.Println("funcA finished")
		}()
		func() { //funcB
			fmt.Println("funcB started")
			time.Sleep(3000 * time.Millisecond)
			fmt.Println("funcB finished")
		}()
	}

	fmt.Println("All processes finished")

}

当然こうなる　output↓

funcA started
--------------0.3秒経過-----------------
--------------0.3秒経過-----------------
--------------0.3秒経過-----------------
funcA finished
funcB started
--------------0.3秒経過-----------------
--------------0.3秒経過-----------------
--------------0.3秒経過-----------------
--------------0.3秒経過-----------------
--------------0.3秒経過-----------------
--------------0.3秒経過-----------------
--------------0.3秒経過-----------------
--------------0.3秒経過-----------------
--------------0.3秒経過-----------------
funcB finished
funcA started
--------------0.3秒経過-----------------
--------------0.3秒経過-----------------
--------------0.3秒経過-----------------
--------------0.3秒経過-----------------
funcA finished
funcB started
--------------0.3秒経過-----------------
--------------0.3秒経過-----------------
--------------0.3秒経過-----------------
--------------0.3秒経過-----------------
--------------0.3秒経過-----------------
--------------0.3秒経過-----------------
--------------0.3秒経過-----------------
--------------0.3秒経過-----------------
--------------0.3秒経過-----------------
funcB finished
funcA started
--------------0.3秒経過-----------------
--------------0.3秒経過-----------------
--------------0.3秒経過-----------------
--------------0.3秒経過-----------------
funcA finished
funcB started
--------------0.3秒経過-----------------
--------------0.3秒経過-----------------
--------------0.3秒経過-----------------
--------------0.3秒経過-----------------
--------------0.3秒経過-----------------
--------------0.3秒経過-----------------
--------------0.3秒経過-----------------
--------------0.3秒経過-----------------
--------------0.3秒経過-----------------
--------------0.3秒経過-----------------
funcB finished
All processes finished

流れ
A → B → A → B → A → B → finished

順序関係なく、とにかく早く終わらせたい

wg.Wait()をfor文の外につけてfuncAとfuncBの頭にgoをつける

package main

import (
	"fmt"
	"sync"
	"time"
)

func main() {
	//時間経過線を入れるためのコード
	go func() {
		for {
			time.Sleep(300 * time.Millisecond) //わかりやすいように0.3秒ごとに線を表示
			fmt.Println("--------------0.3秒経過-----------------")
		}
	}()
	//時間経過線を入れるためのコード終了
	var wg sync.WaitGroup
	for i := 0; i < 3; i++ {
		wg.Add(2)
		go func() { //funcA
			defer wg.Done()
			fmt.Println("funcA started")
			time.Sleep(1000 * time.Millisecond)
			fmt.Println("funcA finished")
		}()
		go func() { //funcB
			defer wg.Done()
			fmt.Println("funcB started")
			time.Sleep(3000 * time.Millisecond)
			fmt.Println("funcB finished")
		}()
	}
    wg.Wait()

	fmt.Println("All processes finished")

}

output↓

funcB started
funcB started
funcA started
funcA started
funcB started
funcA started
--------------0.3秒経過-----------------
--------------0.3秒経過-----------------
--------------0.3秒経過-----------------
funcA finished
funcA finished
funcA finished
--------------0.3秒経過-----------------
--------------0.3秒経過-----------------
--------------0.3秒経過-----------------
--------------0.3秒経過-----------------
--------------0.3秒経過-----------------
--------------0.3秒経過-----------------
funcB finished
funcB finished
funcB finished
All processes finished

3回分のABがほぼ同時にスタートして、時間がかかるBが最後に終了する

for文1サイクル毎にAとBの両方の完了を待ちたい

wg.Wait()をfor文の中につけてfuncAとfuncBの頭にgoをつける


package main

import (
	"fmt"
	"sync"
	"time"
)

func main() {
	//時間経過線を入れるためのコード
	go func() {
		for {
			time.Sleep(300 * time.Millisecond) //わかりやすいように0.3秒ごとに線を表示
			fmt.Println("--------------0.3秒経過-----------------")
		}
	}()
	//時間経過線を入れるためのコード終了
	var wg sync.WaitGroup
	for i := 0; i < 3; i++ {
		wg.Add(2)
		go func() { //funcA
			defer wg.Done()
			fmt.Println("funcA started")
			time.Sleep(1000 * time.Millisecond)
			fmt.Println("funcA finished")
		}()
		go func() { //funcB
			defer wg.Done()
			fmt.Println("funcB started")
			time.Sleep(3000 * time.Millisecond)
			fmt.Println("funcB finished")
		}()
		wg.Wait()
	}

	fmt.Println("All processes finished")

}

output↓

funcB started
funcA started
--------------0.3秒経過-----------------
--------------0.3秒経過-----------------
--------------0.3秒経過-----------------
funcA finished
--------------0.3秒経過-----------------
--------------0.3秒経過-----------------
--------------0.3秒経過-----------------
--------------0.3秒経過-----------------
--------------0.3秒経過-----------------
funcB finished
funcB started
funcA started
--------------0.3秒経過-----------------
--------------0.3秒経過-----------------
--------------0.3秒経過-----------------
--------------0.3秒経過-----------------
funcA finished
--------------0.3秒経過-----------------
--------------0.3秒経過-----------------
--------------0.3秒経過-----------------
--------------0.3秒経過-----------------
--------------0.3秒経過-----------------
--------------0.3秒経過-----------------
funcB finished
funcA started
funcB started
--------------0.3秒経過-----------------
--------------0.3秒経過-----------------
--------------0.3秒経過-----------------
funcA finished
--------------0.3秒経過-----------------
--------------0.3秒経過-----------------
--------------0.3秒経過-----------------
--------------0.3秒経過-----------------
--------------0.3秒経過-----------------
--------------0.3秒経過-----------------
--------------0.3秒経過-----------------
funcB finished
All processes finished

AとBは同時にスタートするが、Bが終了するまで次にはいかない

まとめ

順番通りに実行したい

goroutine使わない

順番関係なく早く処理を終わらせたい

for文の外にwg.Wait()を置く

	var wg sync.WaitGroup
	for i := 0; i < 3; i++ {
		wg.Add(2)
		go func() { //funcA
			defer wg.Done()
			//省略
		}()
		go func() { //funcB
			defer wg.Done()
			//省略
		}()
	}
	wg.Wait()

for文1サイクル毎にAとBの両方の完了を待ちたい

for文の中にwg.Wait()を置く

	var wg sync.WaitGroup
	for i := 0; i < 3; i++ {
		wg.Add(2)
		go func() { //funcA
			defer wg.Done()
			//省略
		}()
		go func() { //funcB
			defer wg.Done()
			//省略
		}()
	wg.Wait()
	}

参考になれば幸いです

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