[dividuum]

I wonder if there's any library out there that uses the SO_REUSEPORT option (see http://lwn.net/Articles/542629/). It allows multiple programs to bind and accept on the same port. So I guess it should be possible to just start a second new process and then gracefully terminate the old one. Any thoughts?

[zimbatm]

You still want some form of coordination to only stop the old process when the new one is live. The best place to be to know about the life of a process is being it's parent process (because you can call wait(pid)) and in that case you might as well open the socket and pass it's fd during fork/exec. That way you keep the cross-POSIX compatibility.