go - 没有任何 goroutine 但仍然得到 "all goroutines are asleep -deadlock"

Question

我正在做一些实验。下面是我的代码。

package main

import (
  "fmt"
  "time"
)

func main(){
  var a chan int
  a = make(chan int)
  for j:=0;j<10;j++{
    firstRoutine(a, j)
    time.Sleep(3 * time.Millisecond)
  }
}

func firstRoutine(chennel chan int, j int){
  i:=0
  fmt.Println("j = ", j, "chennel = ", chennel)
  chennel <- i
}

输出:

F:\Git\GitHub\GO\Prog\Concorrency>go run Channels.go
j =  0 chennel =  <nil>
fatal error: all goroutines are asleep - deadlock!

goroutine 1 [chan send (nil chan)]:
main.firstRoutine(0x0, 0x0)
        F:/Git/GitHub/GO/Prog/Concorrency/Channels.go:24 +0x11f
main.main()
        F:/Git/GitHub/GO/Prog/Concorrency/Channels.go:14 +0x3f
exit status 2

我没有 gorutines在我的程序中，但仍然出现此错误。

下面的程序可以工作，至少没有 goroutine 错误。唯一的变化是 go firstRoutine(a, j)

package main

import (
  "fmt"
  "time"
)

func main(){

  var a chan int
  a = make(chan int)
  for j:=0;j<10;j++{
    go firstRoutine(a, j)
    time.Sleep(3 * time.Millisecond)
  }
}

func firstRoutine(chennel chan int, j int){
  i:=0
  fmt.Println("j = ", j, "chennel = ", chennel)
  chennel <- i
}

输出:

F:\Git\GitHub\GO\Prog\Concorrency>go run Channels.go
j =  0 chennel =  0xc000048060
j =  1 chennel =  0xc000048060
j =  2 chennel =  0xc000048060
j =  3 chennel =  0xc000048060
j =  4 chennel =  0xc000048060
j =  5 chennel =  0xc000048060
j =  6 chennel =  0xc000048060
j =  7 chennel =  0xc000048060
j =  8 chennel =  0xc000048060
j =  9 chennel =  0xc000048060

Answer 1

您正在向 channel 写入/发送数据，但您没有从同一 channel 读取/接收数据。除非您从中读取/写入数据，否则对 channel 的写入/读取会阻塞。

编写一个从 channel a 读取数据的 for 循环或使用缓冲 channel

添加一些日志揭示了第二种情况。

在第二种情况下，您生成了 10 个单独的 go 例程，但由于从未从 channel a 读取数据，因此所有这些例程都被阻塞，并且在 10 次迭代后，for 循环退出，然后是 main 函数。

package main

import (
  "fmt"
  "time"
)

func main(){

  var a chan int
  a = make(chan int)
  for j:=0;j<10;j++{
    go firstRoutine(a, j)
    fmt.Println("sleeping")
    time.Sleep(3 * time.Millisecond)
    fmt.Println("awake")
  }
}

func firstRoutine(chennel chan int, j int){
  i:=0
  fmt.Println("j = ", j, "chennel = ", chennel)
  chennel <- i
  fmt.Println("pushed to channel"); // never gets printed
}

使用缓冲 channel 时:

package main

import (
  "fmt"
  "time"
)

func main(){

  var a chan int
  a = make(chan int, 11) // making a buffered channel of 11 elements
  for j:=0;j<10;j++{
    go firstRoutine(a, j)
    fmt.Println("sleeping")
    time.Sleep(3 * time.Millisecond)
    fmt.Println("awake")
  }
}

func firstRoutine(chennel chan int, j int){
  i:=0
  fmt.Println("j = ", j, "chennel = ", chennel)
  chennel <- i
  fmt.Println("pushed to channel"); // gets printed as buffer is bigger than the iterations, so no blocking
}