On Wed, Oct 24, 2018 at 11:17 AM Sathish VJ <sathis...@gmail.com> wrote: > > Thank you. Would you have an explanation for why it works so differently > from using default?
The codepath that causes the deadlock is : - main reads from c - f() runs select, quit is not writable, so selects default, which starts waiting on c - main waits on quit > > On Wednesday, 24 October 2018 22:44:26 UTC+5:30, Burak Serdar wrote: >> >> You can do this instead: >> >> https://play.golang.org/p/avMIyYlwxbF >> On Wed, Oct 24, 2018 at 11:05 AM Sathish VJ <sath...@gmail.com> wrote: >> > >> > This is a program where the receiver is asking the sender to close after >> > receiving 1 value. Using default for the sending (line 34) causes the >> > code to deadlock while even a timeout of a nanosecond causes it to be ok. >> > I don't want to time the sending though. Is there a better option to >> > sequence this code? >> > Is using default not an option here at all? >> > >> > https://play.golang.org/p/30sI9RYJ1Ed >> > >> > package main >> > >> > import "fmt" >> > //import "time" >> > >> > var c = make(chan string) >> > var quit = make(chan bool) >> > >> > func main() { >> > go fn() >> > >> > for { >> > select { >> > case msg, ok := <-c: >> > if !ok { >> > c = nil >> > return >> > } else { >> > fmt.Println("received: ", msg) >> > quit <- true >> > } >> > } >> > } >> > } >> > >> > func fn() { >> > for { >> > select { >> > case <-quit: >> > fmt.Println("closin chan c") >> > close(c) >> > return >> > //case <-time.After(time.Nanosecond): // this is ok >> > default: // using default causes deadlock >> > c <- "Image" >> > } >> > } >> > } >> > >> > >> > >> > received: Image >> > fatal error: all goroutines are asleep - deadlock! >> > >> > goroutine 1 [chan send]: >> > main.main() >> > /tmp/sandbox497027958/main.go:20 +0x100 >> > >> > goroutine 5 [chan send]: >> > main.fn() >> > /tmp/sandbox497027958/main.go:35 +0x40 >> > created by main.main >> > /tmp/sandbox497027958/main.go:10 +0x40 >> > >> > >> > >> > -- >> > 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...@googlegroups.com. >> > For more options, visit https://groups.google.com/d/optout. > > -- > 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. -- 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.
