英文:
Fibonacci in Go using channels
问题
我正在遵循tour.golang.org上的示例。
我大部分理解这个示例，唯一的问题是为什么当我们向quit通道传递0时它会停止？无论是否将0传递给quit，x始终有一个值。所以选择语句不应该总是执行case 'c <- x'吗？
func fibonacci(c chan int, quit chan int) {
x, y := 0, 1
for {
select {
case c <- x:
x, y = y, x+y
case <-quit:
return
}
}
close(c)
}
func main() {
c := make(chan int)
quit := make(chan int)
go func() {
for i := 0; i < 10; i++ {
fmt.Println(<-c)
}
quit <- 0
}()
fibonacci(c, quit)
}
英文:
I am following the examples on tour.golang.org.
I understand the example mostly, the only issue I have is why does it stop when we pass 0 to quit channel? Regardless of whether 0 was passed to quit, there is always a value for x. So shouldn't select always fall on case 'c <- x' ?
func fibonacci(c chan int, quit chan int) {
x, y := 0, 1
for {
select {
case c <- x:
x, y = y, x+y
case <-quit:
return
}
}
close(c)
}
func main() {
c := make(chan int)
quit := make(chan int)
go func() {
for i := 0; i < 10; i++ {
fmt.Println(<-c)
}
quit <- 0
}()
fibonacci(c, quit)
}
答案1
得分: 2
不，因为这个通道是无缓冲的，发送操作会一直阻塞，直到有接收者可以接收数据。
在《Effective Go》中了解有关通道的内容：
接收者总是会阻塞，直到有数据可接收。**如果通道是无缓冲的，发送者会阻塞，直到接收者接收到值。**如果通道有缓冲区，发送者只会阻塞，直到值被复制到缓冲区；如果缓冲区已满，这意味着等待直到某个接收者取走一个值。
此外，如果在 select 语句中有两个 case 可以执行，会通过伪随机选择一个。
如果一个或多个通信可以进行，将通过均匀的伪随机选择选择一个可以进行的通信。否则，如果有默认 case，将选择该 case。如果没有默认 case，则 "select" 语句将阻塞，直到至少有一个通信可以进行。
英文:
> there is always a value for x. So shouldn't select always fall on case 'c <- x' ?
No, because this channel is unbuffered, the send will block until someone can receive from it.
Read about channels on Effective Go:
> Receivers always block until there is data to receive. If the channel is unbuffered, the sender blocks until the receiver has received the value. If the channel has a buffer, the sender blocks only until the value has been copied to the buffer; if the buffer is full, this means waiting until some receiver has retrieved a value.
Additionally, if 2 cases in a select statement could proceed, one is picked pseudo-randomly.
> If one or more of the communications can proceed, a single one that can proceed is chosen via a uniform pseudo-random selection. Otherwise, if there is a default case, that case is chosen. If there is no default case, the "select" statement blocks until at least one of the communications can proceed.
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