I thought the OP problem was how to kill off the threads in the event of losing connection to the server, so that everything could be restarted again.

No the OP is detaching the threads, so they will simply evaporate when the thread procs "fall off the end" when the while( <$lclient> ) { loops detects that the client has disconnected. (returns undef).

The problem appears to be that the disconnected sockets are remaining active after the threads have gone away--probably due to there being multiple handles in existance that are not being cleaned up properly.