Unable to read from close unbuffered channel

Question

I know we can read from buffered close channels. So, I feel very confident that we can do from unbuffered as well. However, I am not able to test it out.

func test(c chan int) {
    time.Sleep(10 * time.Millisecond)
    close(c)
    fmt.Println(<-c)
}

func main() {
    c := make(chan int)
    go test(c)
    c <- 5
}

Output

panic: send on closed channel

goroutine 1 [running]:
main.main()
        /Users/tanmay.jhazomato.com/Projects/search-service/practice.go:17 +0x85

Process finished with the exit code 2

As far as I know, in this code. First c<-5 should be executed before channel getting closed by test go routine. However, that's not the case. Can somebody tell me when cooperative scheduling is not working here? Why is it that the test go routine is executing first?

Answer 1

A send to an unbuffered channel will block until another goroutine reads from it. So, while the main goroutine is waiting to write to the channel, the second goroutine closes it, and the program fails with a send on the closed channel.