Closed channel or unclosed

Why second time geeting output from channel it appeared that channel closed: false?
Obviously, channel closed: false is equals to cnannel is open. But how it can be open if it has been allready closed?!

ch := make(chan int)
go func() {
ch <- 1
close(ch)
}()
v, isClosed := <-ch
fmt.Printf(“received %d, is channel closed: %v\n”, v, isClosed)
v, isClosed = <-ch
fmt.Printf(“received %d, is channel closed: %v\n”, v, isClosed)

1 Like

Hi @cinematik,

isClosed is not correct here. The second value in a channel is if a value was returned.

See: https://tour.golang.org/concurrency/4

2 Likes

Hi, @cinematik,

The second result from a receive operation is not whether or not the channel is closed but whether the receive was successful: https://golang.org/ref/spec#Receive_operator, making it similar to when you lookup a result from a map: v, ok := a[x]

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The close spec explains the second boolean result very well on receive operator.
https://golang.org/ref/spec#Close

After calling close , and after any previously sent values have been received, receive operations will return the zero value for the channel’s type without blocking. The multi-valued receive operation returns a received value along with an indication of whether the channel is closed.

That means you can use the second untyped boolean variable to check whether the channel closed or not.

@cinematik
If you get False from the receiver operation, it means the channel is closed not open. I recommend you to use ok name to make it more clear and go way.

2 Likes

ok is not a keyword, its just an identifier, that is convtionally used for booleans in the second return value to indicate success.

3 Likes

Right! wrong terminology, ok is not a go keyword. Thanks @NobbZ

1 Like

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