Sockets aren't bad for serialization between threads in Tcl. Generally, a socket opened against localhost in Tcl is pretty smooth running. I have used multicast UDP sockets in anger with Tcl and it ran well.

For stuff that has to be fast, I generally reach for 'C', so I have not plumbed the depths of performance with sockets in Tcl.

Again, though, I drank the "everything is event driven" Kool-Aid years ago and it works for me.