【golang】如何停止向一个已经closed的channel发送数据_golang 避免向close后的channel写入数据-优快云博客

本文讨论了在Go语言中向已关闭的channel发送数据可能导致的问题，并提供了一个使用select和额外stop通道的解决方案，以更优雅地停止写入操作。通过在default分支中处理写入，当接收到停止信号时，可以立即停止，避免了错误的发生。

golang中向一个closed的channel中发送数据，会造成严重“事故”。也是容易犯的常见毛病。

错误示范：

package main

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

var mu sync.Mutex
var isChanClosed = false

func setClosedFlag() {
	mu.Lock()
	isChanClosed = true
	mu.Unlock()
}

func getClosedFlag() bool {
	mu.Lock()
	defer mu.Unlock()
	return isChanClosed
}

func main() {

	ch := make(chan int, 10)
	//write
	go func() {
		for i := 0; i < 20; i++ {
			flag := getClosedFlag()
			if flag == true {
				return
			}
			fmt.Println(" before write isChanClosed:", flag)
			ch <- i
			time.Sleep(time.Millisecond * 100)
		}

		fmt.Println(" not write.....")
	}()

	//read
	go func() {
		for {
			time.Sleep(time.Millisecond * 500)
			m, ok := <-ch
			if ok {
				fmt.Println("channel not closed m=", m)
			} else {
				fmt.Println("channel closed, left elem's len:", len(ch))
				for m := range ch {
					fmt.Println("  left:  %d", m)
				}

			}
		}

	}()

	time.Sleep(5 * time.Second)

	setClosedFlag()
	close(ch)
	fmt.Println(">>>>> closed channel,  isChanClosed:", getClosedFlag())
	time.Sleep(time.Second * 300)
}

运行后：

根据flag 判断条件，write 之前是false 没有关闭, write时 channel 关闭了。报错。感觉根据flag来判断还是“慢“了点。

一种解决方案：使用select ,并将write 功能放在 default 分支中。


func main() {

	ch := make(chan int, 10)
	stop := make(chan bool)
	//write
	go func() {
		for {
			select {
			case <-stop:
				fmt.Println("ch closed. stop receive data")
				return

			default:
			 
				for i := 0; i < 20; i++ {
					flag := getClosedFlag()
					if flag == true {
						return
					}
					fmt.Println(" before write isChanClosed:", flag)
					ch <- i
					time.Sleep(time.Millisecond * 100)
				}
				fmt.Println(" not write.....")

			}
		}
	}()

	//read
	go func() {
		for {
			time.Sleep(time.Millisecond * 500)
			m, ok := <-ch
			if ok {
				fmt.Println("channel not closed m=", m)
			} else {
				fmt.Println("channel closed, left elem's len:", len(ch))
				for m := range ch {
					fmt.Println("  left:  %d", m)
				}
			}
		}
	}()

	time.Sleep(5 * time.Second)
	stop <- true
	close(ch)
	fmt.Println(">>>>> closed channel,  isChanClosed:", getClosedFlag())
	time.Sleep(time.Second * 300)
}

运行结果：