I am learning Go and I am on channels now. I have written a simple program using channels. I have created two channels and the channels are passed to a function which is called concurrently.
My expectation is to print output form both the channels but in reality only one channel output is getting printed:
package main
import "fmt"
func square(dat int, ch chan<- int) {
ch <- dat * dat
}
func main() {
resp1 := make(chan int)
resp2 := make(chan int)
go square(20, resp1)
go square(10, resp2)
select {
case msg1 := <-resp1:
fmt.Println(msg1)
case msg2 := <-resp2:
fmt.Println(msg2)
}
}
Either the message from resp1 is printed or that from resp2 during each execution. Channels should block until something is pushed into it, right?
The Go Programming Language Specification
A "select" statement chooses which of a set of possible send or receive operations will proceed.
Select chooses one of a set. For example,
package main
import "fmt"
func square(dat int, ch chan<- int) {
ch <- dat * dat
}
func main() {
resp1 := make(chan int)
resp2 := make(chan int)
go square(20, resp1)
go square(10, resp2)
// Choose one
select {
case msg1 := <-resp1:
fmt.Println(msg1)
case msg2 := <-resp2:
fmt.Println(msg2)
}
// Choose the other
select {
case msg1 := <-resp1:
fmt.Println(msg1)
case msg2 := <-resp2:
fmt.Println(msg2)
}
}
Playground: https://play.golang.org/p/TiThqcXDa6o
Output:
100
400