英文:
All goroutines are asleep when reading from buffered channel
问题
func writeToChan(wg *sync.WaitGroup, ch chan int, stop int) {
defer wg.Done()
for i := 0; i < stop; i++ {
ch <- i
}
}
func readToChan(wg *sync.WaitGroup, ch chan int) {
defer wg.Done()
for n := range ch {
fmt.Println(n)
}
}
func main() {
ch := make(chan int, 3)
wg := new(sync.WaitGroup)
wg.Add(2)
go writeToChan(wg, ch, 5)
go readToChan(wg, ch)
wg.Wait()
}
0
1
2
3
4
fatal error: all goroutines are asleep - deadlock!
我假设readToChan
函数总是连续读取,而writeToChan
函数在向通道写入数据后会等待通道被读取。
我不知道为什么输出显示死锁,尽管我已经在WaitGroup
中添加了两个wait
操作。
英文:
func writeToChan(wg *sync.WaitGroup, ch chan int, stop int) {
defer wg.Done()
for i := 0; i < stop; i++ {
ch <- i
}
}
func readToChan(wg *sync.WaitGroup, ch chan int) {
defer wg.Done()
for n := range ch {
fmt.Println(n)
}
}
func main() {
ch := make(chan int, 3)
wg := new(sync.WaitGroup)
wg.Add(2)
go writeToChan(wg, ch, 5)
go readToChan(wg, ch)
wg.Wait()
}
0
1
2
3
4
fatal error: all goroutines are asleep - deadlock!
I assume that the readToChan
always reads continuously, and the writeToChan
write to the channel and waits while the channel is read.
I don't know why the output showed deadlock while I added two 'wait' to the WaitGroup.
答案1
得分: 2
你需要在发送方关闭通道。
使用以下代码:
for n := range ch {
fmt.Println(n)
}
只有当ch
被关闭时,循环才会停止。
正确的示例代码如下:
package main
import (
"fmt"
"sync"
)
func writeToChan(wg *sync.WaitGroup, ch chan int, stop int) {
defer wg.Done()
for i := 0; i < stop; i++ {
ch <- i
}
close(ch)
}
func readToChan(wg *sync.WaitGroup, ch chan int) {
defer wg.Done()
for n := range ch {
fmt.Println(n)
}
}
func main() {
ch := make(chan int, 3)
wg := new(sync.WaitGroup)
wg.Add(2)
go writeToChan(wg, ch, 5)
go readToChan(wg, ch)
wg.Wait()
}
英文:
You need to close channel at the sender side.
By using
for n := range ch {
fmt.Println(n)
}
The loop will only stop when ch
is closed
correct example:
package main
import (
"fmt"
"sync"
)
func writeToChan(wg *sync.WaitGroup, ch chan int, stop int) {
defer wg.Done()
for i := 0; i < stop; i++ {
ch <- i
}
close(ch)
}
func readToChan(wg *sync.WaitGroup, ch chan int) {
defer wg.Done()
for n := range ch {
fmt.Println(n)
}
}
func main() {
ch := make(chan int, 3)
wg := new(sync.WaitGroup)
wg.Add(2)
go writeToChan(wg, ch, 5)
go readToChan(wg, ch)
wg.Wait()
}
答案2
得分: 0
如果没有在缓冲通道上调用close函数,读取器就不知道何时停止读取。请查看以下示例,其中使用for和select调用来处理多个通道。
https://go.dev/play/p/Lx5g9o4RsqW
package main
import (
"fmt"
"sync"
"time"
)
func writeToChan(wg *sync.WaitGroup, ch chan int, stop int, quit chan<- bool) {
defer func() {
wg.Done()
close(ch)
fmt.Println("write wg done")
}()
for i := 0; i < stop; i++ {
ch <- i
fmt.Println("write:", i)
}
fmt.Println("write done")
fmt.Println("sleeping for 5 sec")
time.Sleep(5 * time.Second)
quit <- true
close(quit)
}
func readToChan(wg *sync.WaitGroup, ch chan int, quit chan bool) {
defer func() {
wg.Done()
fmt.Println("read wg done")
}()
for {
select {
case n := <-ch:
fmt.Println("read:", n)
case val := <-quit:
fmt.Println("received quit:", val)
return
}
}
}
func main() {
ch := make(chan int, 5)
ch2 := make(chan bool)
wg := new(sync.WaitGroup)
wg.Add(2)
go writeToChan(wg, ch, 3, ch2)
go readToChan(wg, ch, ch2)
wg.Wait()
}
输出:
write: 0
write: 1
write: 2
write done
sleeping for 5 sec
read: 0
read: 1
read: 2
write wg done
received quit: true
read wg done
程序已退出。
英文:
If close is not called on buffered channel, reader doesn't know when to stop reading.
Check this example with for and select calls(to handle multi channels).
https://go.dev/play/p/Lx5g9o4RsqW
package main
import (
"fmt"
"sync"
"time")
func writeToChan(wg *sync.WaitGroup, ch chan int, stop int, quit chan<- bool) {
defer func() {
wg.Done()
close(ch)
fmt.Println("write wg done")
}()
for i := 0; i < stop; i++ {
ch <- i
fmt.Println("write:", i)
}
fmt.Println("write done")
fmt.Println("sleeping for 5 sec")
time.Sleep(5 * time.Second)
quit <- true
close(quit)
}
func readToChan(wg *sync.WaitGroup, ch chan int, quit chan bool) {
defer func() {
wg.Done()
fmt.Println("read wg done")
}()
//using rang over
//for n := range ch {
// fmt.Println(n)
//}
//using Select if you have multiple channels.
for {
//fmt.Println("waiting for multiple channels")
select {
case n := <-ch:
fmt.Println("read:", n)
// if ok == false {
// fmt.Println("read done")
// //return
// }
case val := <-quit:
fmt.Println("received quit :", val)
return
// default:
// fmt.Println("default")
}
}
}
func main() {
ch := make(chan int, 5)
ch2 := make(chan bool)
wg := new(sync.WaitGroup)
wg.Add(2)
go writeToChan(wg, ch, 3, ch2)
go readToChan(wg, ch, ch2)
wg.Wait()
}
Output:
write: 0
write: 1
write: 2
write done
sleeping for 5 sec
read: 0
read: 1
read: 2
write wg done
received quit : true
read wg done
Program exited.
通过集体智慧和协作来改善编程学习和解决问题的方式。致力于成为全球开发者共同参与的知识库,让每个人都能够通过互相帮助和分享经验来进步。
评论