Well, the only non-polling way I can think of is for the server to call the client. Which is kinda backwards, isn't it?

I don't like polling in general either, but one has to have a sense of proportion. A process that polls once per second for, say 10 seconds (doing sleep 1 each time), is going to create much less engine load than a process that polls in a tight, milisecond loop.

But you don't need a tight loop - if the server runs for an extra second before the first client starts, nothing bad will happen.

On the other hand if you insist on creating a complicated solution just to avoid polling, you will needlessly complicate the server and spend much, much more of your time than you will save with the automated startup script.