"on Unix its not the _only_ way" Options were more limited in early unix. Use of signals as an adhoc IPC mechanism predates BSD sockets api (1983). Poll has so

"on Unix its not the _only_ way" Options were more limited in early unix. Use of signals as an adhoc IPC mechanism predates BSD sockets api (1983). Poll has something to do with SysV, so would have been later. There may have been other IPC mechanisms that were dropped before modern unix (but presumably dropped for good reasons). Art of Unix Programming refers to one called mx.