Libdill IO is nonblocking and calls returns a channel. Reading from the channel yields the coroutine, similar to the await statement in some languages.

oh cool ! does that happen for read/write to non-socket fd’s as well ?

Yeah, see the file descriptors section on this page http://libdill.org/documentation.html

i did before posting here, and could not find anything that might have indicated that i.e. non-socket-fd reads end up with coroutine like semantics...