英文:
Golang timeout is not executed with channels
问题
我正在使用goroutines/channels。以下是你的代码：
func main() {
c1 := make(chan int, 1)
go func() {
for {
time.Sleep(1500 * time.Millisecond)
c1 <- 10
}
}()
go func() {
for {
select {
case i := <-c1:
fmt.Println(i)
case <-time.After(2000 * time.Millisecond):
fmt.Println("TIMEOUT") // <-- Not Executed
}
}
}()
fmt.Scanln()
}
为什么超时的情况没有被执行？
英文:
I am using goroutines/channels.
Here is my code.
Why is the timeout case not getting executed?
func main() {
c1 := make(chan int, 1)
go func() {
for {
time.Sleep(1500 * time.Millisecond)
c1 <- 10
}
}()
go func() {
for {
select {
case i := <-c1:
fmt.Println(i)
case <-time.After(2000 * time.Millisecond):
fmt.Println("TIMEOUT") // <-- Not Executed
}
}
}()
fmt.Scanln()
}
答案1
得分: 4
你的超时不会发生，因为你的一个goroutine会在每1.5秒（左右）重复地向c1通道发送一个值，只有当c1中没有要接收的值时，超时才会发生。
一旦从c1接收到一个值，在下一次执行select时，将会进行一个新的time.After()调用，它会返回一个新的通道，该通道只会在另外2秒后发送一个值。上一个select执行的超时通道将被丢弃，不再使用。
要在2秒后接收超时，只需创建一次超时通道，例如：
timeout := time.After(2000 * time.Millisecond)
for {
select {
case i := <-c1:
fmt.Println(i)
case <-timeout:
fmt.Println("TIMEOUT") // 2秒后执行
}
}
输出：
10
TIMEOUT
10
10
10
...
英文:
Your timeout doesn't happen, because one of your goroutine sends a value on your c1 channel in every 1.5 seconds (or so) repeatedly, and your timeout would only happen if there is no value to be received from c1 for 2 seconds.
Once a value is received from c1, in the next iteration executing select again a new time.After() call will be made which which returns a new channel on which a value will only be sent after another 2 seconds. The timeout channel from the previous select execution is discarded and is not used anymore.
To receive the timeout after 2 seconds, create the timeout channel only once, e.g.:
timeout := time.After(2000 * time.Millisecond)
for {
select {
case i := <-c1:
fmt.Println(i)
case <-timeout:
fmt.Println("TIMEOUT") // Will get executed after 2 sec
}
}
Output:
10
TIMEOUT
10
10
10
...
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