Here is a sleepless version. The channel is still unbuffered, but this should be OK since reading from channel is done in main(). Thus, factorial() writes the result to the channel, and main() reads it from there. As result main() does not end before factorial() is completed.
https://play.golang.org/p/nTQxU9GnDPj package main import ( "fmt" ) func main() { d := make(chan int) go factorial(5, d) fmt.Println("waiting ...") fmt.Println(<-d) fmt.Println("Game over", d) } func factorial(n int, d chan int) { fmt.Println("function starting...") var a int = 1 for ; n > 0; n-- { a *= n } fmt.Println("result=", a) d <- a } <https://play.golang.org/p/nTQxU9GnDPj> Am Do., 19. Aug. 2021 um 18:35 Uhr schrieb jake...@gmail.com < jake6...@gmail.com>: > Jan is correct, and you should probably use a sync.WaitGroup to keep your > main() alive. > > But even if you do that, you have a bigger problem. You channel is > unbuffered. That means that `d <- a` will block until someone reads from d. > Since `factorial` is the only goroutine that uses d, that line will block > forever. (Of course, in your code, main() will exit after 3 seconds, so > forever is short.) You can 'fix' the code by changing to a buffered > channel, like: `d := make(chan int, 1)`. Then your code works, since the > send will no longer block. Although it is pretty pointless to read from a > channel in the same goroutine that writes to it. > > A more common use would be for the goroutine to send the result back to > main, like this: https://play.golang.org/p/yJHJWhYif5h > Note that, in this case, the channel read keeps main() from exiting before > factorial() is finished. > > On Thursday, August 19, 2021 at 10:43:32 AM UTC-4 muhorto...@gmail.com > wrote: > >> I just started practicing with channels, after writing to the channel, >> nothing is output from there >> func main() { >> d := make(chan int) >> go factorial(5, d) >> time.Sleep(3 * time.Second) >> } >> >> func factorial(n int, d chan int) { >> fmt.Println("function starting...") >> time.Sleep(3 * time.Second) >> var a int = 1 >> for ; n > 0; n-- { >> a *= n >> } >> d <- a // //nothing works after that >> fmt.Println(<-d) >> fmt.Println(a) >> } >> >> -------------------------------------------------------------------------------------------------------------------------------------------- >> Another question I want to make a recursive function with a factorial, >> pass it to goroutine in main. But I do not know if it is possible to >> somehow combine *return* and a channel in the declaration of arguments. >> >> --------------------------------------------------------------------------------------------------------------------------------------------- >> if I first pass in something to the channel from main, >> a lock occurs.Why? So it's not possible at all? >> > -- > 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. > To view this discussion on the web visit > https://groups.google.com/d/msgid/golang-nuts/e81505fe-3415-4eb0-acf0-4b208e42fa13n%40googlegroups.com > <https://groups.google.com/d/msgid/golang-nuts/e81505fe-3415-4eb0-acf0-4b208e42fa13n%40googlegroups.com?utm_medium=email&utm_source=footer> > . > -- 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. To view this discussion on the web visit https://groups.google.com/d/msgid/golang-nuts/CA%2B8p0G1BuEjEOXjG%2BJr_xCU_5ekzR0KCgkeAaMAYXPkbm3h7Hw%40mail.gmail.com.
