Pipeline is composited by many Generator.
There is a marked comment in example, you could try to uncomment it, you will see the program exit after 1 second because it has closed done channel.
This demos when generator doesn't have i < 10 condition, and we hope there is no any goroutine leaks. So, remember to add done channel or cancelable context into goroutine creator to avoid the goroutine leaks.
Refer Pipeline Example Code