sendmsg_nonblock

        # BasicSocket.sendmsg_nonblock

(from ruby core)
---
    basicsocket.sendmsg_nonblock(mesg, flags=0, dest_sockaddr=nil, *controls, opts={}) => numbytes_sent

---

sendmsg_nonblock sends a message using sendmsg(2) system call in
non-blocking manner.

It is similar to BasicSocket#sendmsg but the non-blocking flag is set
before the system call and it doesn't retry the system call.

By specifying a keyword argument *exception* to `false`, you can
indicate that sendmsg_nonblock should not raise an IO::WaitWritable
exception, but return the symbol `:wait_writable` instead.