go - How can I stop the goroutine based on the returned value from that goroutine -

like here created go playground sample: sggxeh40ev, cannot work.

quit := make(chan bool) res := make(chan int)  go func() {     idx := 0     {         select {         case <-quit:             fmt.println("detected quit signal!")             return         default:             fmt.println("goroutine doing stuff..")             res <- idx             idx++         }     }  }()  r := range res {     if r == 6 {         quit <- true     }     fmt.println("i received: ", r) } 

output:

goroutine doing stuff.. goroutine doing stuff.. received:  0 received:  1 goroutine doing stuff.. goroutine doing stuff.. received:  2 received:  3 goroutine doing stuff.. goroutine doing stuff.. received:  4 received:  5 goroutine doing stuff.. goroutine doing stuff.. fatal error: goroutines asleep - deadlock! 

is possible? wrong

the problem in goroutine use select check if should abort, use default branch work otherwise.

the default branch executed if no communications (listed in case branches) can proceed. in each iteration quit channel checked, if cannot received (no need quit yet), default branch executed, unconditionally tries send value on res. if main goroutine not ready receive it, deadlock. , happens when sent value 6, because main goroutine tries send value on quit, if worker goroutine in default branch trying send on res, both goroutines try send value, , none trying receive! both channels unbuffered, deadlock.

in worker goroutine must send value on res using proper case branch, , not in default branch:

select { case <-quit:     fmt.println("detected quit signal!")     return case res <- idx:     fmt.println("goroutine doing stuff..")     idx++ } 

and in main goroutine must break out for loop main goroutine can end , program can end well:

if r == 6 {     quit <- true     break } 

output time (try on go playground):

goroutine doing stuff.. received:  0 received:  1 goroutine doing stuff.. goroutine doing stuff.. received:  2 received:  3 goroutine doing stuff.. goroutine doing stuff.. received:  4 received:  5 goroutine doing stuff.. goroutine doing stuff..