go 为什么这样的代码会产生死锁问题

V2EX = way to explore

V2EX 是一个关于分享和探索的地方

现在注册

已注册用户请登录

这是一个创建于 1009 天前的主题，其中的信息可能已经有所发展或是发生改变。

按道理 main 结束之前启动的 goroutine 不会结束，如果不发送 stopCh ，则会一直阻塞，为啥会提示有死锁

package main

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

var wg sync.WaitGroup

func main() {
	fmt.Print("hello world\n")
	ch1 := make(chan int)
	ch2 := make(chan int)
	stopCh := make(chan struct{})
	wg.Add(1)
	go work(ch1, ch2, stopCh)
	ch1 <- 1
	ch2 <- 1
	time.Sleep(1000 * time.Millisecond)
	// stopCh <- struct{}{}
	var a int

	wg.Wait()
	fmt.Scan(&a)
}
func work(ch1, ch2 chan int, stopCh <-chan struct{}) {
	defer wg.Done()
	for {
		select {
		case <-stopCh:
			return
		case job1 := <-ch1:
			fmt.Println("receive ch1 on first loop:", job1)
		case job2 := <-ch2:
		priority:
			for {
				select {
				case job1 := <-ch1:
					fmt.Println("receive ch1 on second loop:", job1)
				default:
					time.Sleep(1000 * time.Millisecond)
					break priority
				}
			}
			// 执行 job1 的内容
			fmt.Println("receive ch2:", job2)
		}
	}
}

运行之后报错

hello world
receive ch1 on first loop: 1
receive ch2: 1
fatal error: all goroutines are asleep - deadlock!

goroutine 1 [semacquire]:
sync.runtime_Semacquire(0xd77c28)
        C:/go/src/runtime/sema.go:56 +0x49
sync.(*WaitGroup).Wait(0xd77c20)
        C:/go/src/sync/waitgroup.go:130 +0x6b
main.main()
        F:/code/go/c2c/client/client.go:24 +0x1b6

goroutine 6 [select]:
main.work(0xc000014180, 0xc0000141e0, 0xc000014240)
        F:/code/go/c2c/client/client.go:30 +0x26e
created by main.main
        F:/code/go/c2c/client/client.go:17 +0x146
exit status 2

11 条回复 • 2022-02-14 12:58:04 +08:00