Hi Twisted list! I have a library that is attempting to start an AsyncioSelectorReactor, fork the process, and then open a network socket on macOS. When the network socket is opened, Twisted throws an [Errno 9] "Bad file descriptor" exception at me. I get no such exception on Ubuntu. If I change the sequence from: setup_reactor('AsyncioSelectorReactor') fork_and_continue_in_child() run_server() to: fork_and_continue_in_child() # fork first setup_reactor('AsyncioSelectorReactor') run_server() Then everything works okay. Also if I use SelectReactor rather than AsyncioSelectorReactor then it doesn't matter which order I fork in. So my question is, does Twisted support being forked after starting a reactor or not? -- David Foster | Seattle, WA, USA P.S. For more details see this Django Channels thread: https://github.com/django/channels/issues/962#issuecomment-414103367