通道 - biuaxia

標題：Channel 通道
日期：2022-06-29 14:39:00
toc：false
index_img：http://api.btstu.cn/sjbz/?lx=m_dongman&cid=7
類別：

Go
標籤：
解決
次數
指針

切記：不要通過共享內存通信，通過通信來共享內存

所有 channel 的發送操作都是阻塞的（又叫 block）
使用 waiteGroup 一定要配合指針使用
解決實際問題一定要基於並發不能保證有序或無序的情況去排查

直接上代碼，注意看註釋：

package main

import "fmt"

type worker struct {
	in   chan int
	done chan bool
}

func main() {
	const count = 4

	var workers [count]worker
	for i := 0; i < count; i++ {
		workers[i] = createWorker(i)
	}

	for i, worker := range workers {
		worker.in <- 'a' + i
	}

	for i, worker := range workers {
		worker.in <- 'A' + i
	}

	for _, worker := range workers {
		<-worker.done
		<-worker.done
	}
}

func doWork(id int, w worker) {
	for {
		fmt.Printf("No.%d worker received: %c\n", id, <-w.in)
		go func() { w.done <- true }() // 還可以建立有緩衝的通道來解決，這裡就和 done: make(chan bool, 1) 是一樣的效果，不再阻塞在這裡，結果無序
		// w.done <- true
	}
}

func createWorker(id int) worker {
	w := worker{
		in:   make(chan int),  // 加在 in 通道可以讓兩次數據都發送完，開啟了兩次 done 的接收，結果無序
		done: make(chan bool), // 加在 done 通道可以讓第一次數據發送完，就直接開啟第二次數據發送，結果無序
	}
	go doWork(id, w)
	return w
}

使用 sync.WaitGroup 實現：

package main

import (
	"fmt"
	"sync"
)

type worker struct {
	in   chan int
	done *sync.WaitGroup
}

func main() {
	const count = 4

	var wg sync.WaitGroup

	var workers [count]worker
	for i := 0; i < count; i++ {
		workers[i] = createWorker(i, &wg)
	}

	wg.Add(count * 2)
	for i, worker := range workers {
		worker.in <- 'a' + i
	}

	for i, worker := range workers {
		worker.in <- 'A' + i
	}

	wg.Wait()
}

func doWork(id int, w worker) {
	for {
		fmt.Printf("No.%d worker received: %c\n", id, <-w.in)
		w.done.Done()
	}
}

func createWorker(id int, wg *sync.WaitGroup) worker {
	w := worker{
		in:   make(chan int),
		done: wg,
	}
	go doWork(id, w)
	return w
}

將函數與 WaitGroup 一起使用：

package main

import (
	"fmt"
	"sync"
)

type worker struct {
	in   chan int
	done func()
}

func main() {
	const count = 4

	var wg sync.WaitGroup

	var workers [count]worker
	for i := 0; i < count; i++ {
		workers[i] = createWorker(i, &wg)
	}

	wg.Add(count * 2)
	for i, worker := range workers {
		worker.in <- 'a' + i
	}

	for i, worker := range workers {
		worker.in <- 'A' + i
	}

	wg.Wait()
}

func doWork(id int, w worker) {
	for {
		fmt.Printf("No.%d worker received: %c\n", id, <-w.in)
		w.done()
	}
}

func createWorker(id int, wg *sync.WaitGroup) worker {
	w := worker{
		in:   make(chan int),
		done: wg.Done,
	}
	go doWork(id, w)
	return w
}