[HACKERS] Persistent wait event sets and socket changes

I've been looking into the wait event set interface added in 9.6 with an eye to using it in an extension that maintains a set of non-blocking libpq connections to other PostgreSQL instances.

In the process I've been surprised to find that there does not appear to be any interface to remove a socket once added to the wait event set, or replace it with a new socket.

ModifyWaitEvent(...) doesn't take a pgsocket. There doesn't seem to be a way to remove an event from the set either.

Discussion in https://www.postgresql.org/message-id/flat/20160114143931.GG10941%40awork2.anarazel.de talks about a proposed SetSocketToWaitOn(...)/AddSocketToWaitSet and

RemoveSocketFromWaitSet etc. But it looks like it petered out and went nowhere, apparently mainly due to not being needed by any current core users.

See:

* https://www.postgresql.org/message-id/CA%2BTgmoZ_2EgBCXinHsJn%3Dv8bfg3Y3uXpG1xHiQ8g7yRJzwt3Yg%40mail.gmail.com

* https://www.postgresql.org/message-id/CAEepm%3D14htYKhJ67OEvX%3DXmtiB5677K6ehQACH1ySkebeYh8Nw%40mail.gmail.com

I'd like to add such interfaces at some point, but for now can work around it by destroying and re-creating the wait event set when the fd-set changes. So I'm posting mostly to confirm that it's not supposed to work, and ask if anyone thinks I should submit a comment patch to latch.c documenting it.
--