Two cases:

1. With gtk: I add the socket(s) to the pending events queue. In this case the gtk main loop takes care of giving up the CPU.
2. In "straight perl" you can ask the socket to signal you (use fcntl with F_SETSIG to tell the socket what signal to send) when there is input then do a wait (which can be interrupted by a signal). The wait gives up the CPU, the signal tells the system to reschedule your process. DisclaimerActiveState does not have F_SETSIG so this won't work with that Windows port. It may or may not work with any other.

HTH, --traveler