go 发生死锁的问题

[liu826250634]

package main

import (
	"fmt"
	"math/rand"
	"sync"
	"time"
)

var wg sync.WaitGroup

//计算一个 64 位随机数的各位的和
func randNumber(x int64) int64 {
	var sum int64 = 0
	for x > 0 {
		a := x % 10
		x = x / 10
		sum += a
	}
	return sum
}

func main() {
	wg.Add(25)
	var jobChan = make(chan int64, 10)
	var resultChan = make(chan int64, 10)
	go func(jobChan chan<- int64, ) {
		defer wg.Done()
		for i:=0;i<1000;i++{
			rand.Seed(time.Now().UnixNano())
			jobChan <- rand.Int63n(100)
		}
	}(jobChan)

	for i:=0;i<24;i++{
		go func(jobChan <-chan int64, resultChan chan<- int64, ) {
			defer wg.Done()
			for num:= range jobChan{
				resultChan <- randNumber(num)
			}
		}(jobChan, resultChan)
	}

	for i:= range resultChan{
		fmt.Println(i)
	}
	wg.Wait()
}


发生错误：fatal error: all goroutines are asleep - deadlock!
请教一下，为什么会发生死锁的情况？

[linjunyi22]

```go
package main

import (
"fmt"
"math/rand"
"sync"
"time"
)

var wg sync.WaitGroup

//计算一个 64 位随机数的各位的和
func randNumber(x int64) int64 {
var sum int64 = 0
for x > 0 {
a := x % 10
x = x / 10
sum += a
}
return sum
}

func main() {
wg.Add(25)
var jobChan = make(chan int64, 10)
var resultChan = make(chan int64, 10)
go func(jobChan chan<- int64, ) {
defer wg.Done()
for i := 0; i < 1000; i++ {
rand.Seed(time.Now().UnixNano())
jobChan <- rand.Int63n(100)
}
close(jobChan) // 此处要关闭 jobChan，否则在 jobChan 的 range 遍历中会一直阻塞
}(jobChan)

for i := 0; i < 24; i++ {
go func(jobChan <-chan int64, resultChan chan<- int64, ) {
defer wg.Done()
for num := range jobChan {
resultChan <- randNumber(num)
}
}(jobChan, resultChan)
}
// 此处 resultChan 的遍历放到一个 goroutine 中执行，让 wg 的 wait 执行完后主协程直接退出
// 如果放在主协程中，也没有关闭 resultChan 的话，也会造成阻塞，就会产生死锁
go func() {
for i := range resultChan {
fmt.Println(i)
}
}()
wg.Wait()
}
```

[beidounanxizi]

去看看 waitgroup 实现吧

[evill]

channel 没有关闭
for num:= range jobChan
永远不会退出

[zjj19950716]

for num:= range jobChan{
resultChan <- randNumber(num)
}
job 1000 个发完之后，这边还一直卡主。
最后的 Wait()也没意义,从 resultChan 读那里也退不出来

[asAnotherJack]

原因就是 2l 说的那样，因为 jobChan 和 resultChan 没有 close 阻塞在循环里了，jobChan 就像 2l 那样处理，resultChan 的处理，可以在 wg.Wait()后边 close resultChan，然后再 range resultChan 打印结果

[liu826250634]

@linjunyi22 感谢， 刚学习 go，有一些概念改搞不清。但是你这种方法好像会造成接收不完全就会退出。我自己也解决了这个问题了。

```
package main

import (
"context"
"fmt"
"math/rand"
"sync"
"time"
)

var (
wg = sync.WaitGroup{} // 用于计数， 让程序正常执行，不会主函数执行完子函数还没执行。计数清 0 则不用等待
a int
//lock sync.Mutex
rwlock sync.RWMutex
icons map[string]string
loadIconsOnce sync.Once
//m sync.Map
)

func randNumber(x int64) int64 {
var sum int64 = 0
for x > 0 {
a := x % 10
x = x / 10
sum += a
}
return sum
}


func main() {
wg.Add(25)
defer wg.Wait()
var maxSend = 10
var jobChan = make(chan int64, 10)
var resultChan = make(chan int64, 10)
var lock sync.Mutex
ctx, cancel := context.WithCancel(context.Background())

//var once sync.Once
go func(jobChan chan<- int64, ) {
for i:=0;i<maxSend;i++{
rand.Seed(time.Now().UnixNano())
jobChan <- rand.Int63n(100)
}
close(jobChan)
wg.Done()
}(jobChan)

count1 := 1
for i:=0;i<24;i++{
go func(jobChan <-chan int64, resultChan chan int64, ctx context.Context) {
defer wg.Done()
for num:= range jobChan{
select {
case <- ctx.Done():
return
case resultChan <- randNumber(num):
lock.Lock()
fmt.Println("count:", count1)
count1 += 1
lock.Unlock()
}

}
}(jobChan, resultChan, ctx)
}

num := maxSend
count := 1
for value := range resultChan {
if num == 1 {
fmt.Printf("key:%v, value:%v\n", count, value)
cancel()
return
}else {
num -= 1
fmt.Printf("key:%v, value:%v\n", count, value)
count += 1
}
}
}

```

[liu826250634]

回复中， 写代码怎么 md 不生效了= =