It's neither meaningful nor safe. :)
Since you're writing a variable that can be read in another goroutine
without establishing any sort of ordering, this code is unsafe. The issue
happens with any code like:
func main() {
var ch chan int
go func() { <-ch }()
ch = make(chan int)
}
The spawned goroutine's read of `ch` isn't ordered with respect to the
write of `ch` in the main goroutine, so you have a data race. You can
verify this yourself by running the above code with `go run -race main.go`.
(Also note that, if you move the assignment of `ch` above the `go func()
...`, the race goes away. That's because starting a goroutine enforces an
order of events).
Next, quoting [the spec](https://golang.org/ref/spec#Select_statements):
"For all the cases in the [select] statement, the channel operands of
receive operations [...] are evaluated exactly once."
So, it seems that the compiler is required to save the value of `signal` as
soon as you enter your `select` statement. As a result, when you update it
later, none of the goroutines that were in the `select` statement would
notice, since they're all trying to read from the original "blocked"
channel. See: https://play.golang.org/p/jpe_oNHGGY
George
On Saturday, September 3, 2016 at 6:39:27 AM UTC-7, Uvelichitel wrote:
>
> Hi.
> Closing channel to broadcast Cancellation or Done event is proven
> pattern in Go.
>
> go func(){
> for{
> select{
> case <-signal:
> //canselation
> default:
> //default
> }
> }
> }
> //...
> close(signal)
>
> But we can signal only once this way. May we cheat a bit?
>
> var closed = make(chan struct{})
> close(closed)
> var blocked chan struct{}
> var signal chan struct{}
> //and than switch to emit events
> signal = closed
> //...
> signal = blocked
> //...
> signal = closed
> //...
> signal = blocked
>
> Does it considered meaningful or/and at least safe?
> --
> Ilya Kostarev
>
--
You received this message because you are subscribed to the Google Groups
"golang-nuts" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to golang-nuts+unsubscr...@googlegroups.com.
For more options, visit https://groups.google.com/d/optout.
