feature: support for add/remove single flag in event set

[KarthikNedunchezhiyan]

It would be helpful if the event-manager support add/remove individual flag from the existing one (instead of whole) or support for getting previously registered flags.

Some use case is we send more data via vsock (async mode) so, we need to add EventSet::OUT flag additionally whenever we experience WouldBlock error.

[alexandruag]

This makes sense, but I'm not sure what the right prioritization is :-s Does the status quo cause significant pain for the use cases you have in mind? (I guess the current alternative is for the subscriber to keep track of the event flags and then process and use mod to change the entire set)

[KarthikNedunchezhiyan]

I guess the current alternative is for the subscriber to keep track of the event flags and then process and use mod to change the entire set

@alexandruag it is possible but in our case we have lots of events under single subscribers. each time we add/update the event_set of fd, we need to update the subscriber code also (to track of recently updated event_set for a fd).

We have lots of individual subscriber code, so we need to perform above operation on all subscribers. which makes a code duplication. To avoid code duplication we need to write a wrapper over event-manager so, that the wrapper will keep track of latest event_set for all fd associated.

IMO, The above complexity will be removed if this is natively supported by event-manager.

[alexandruag]

Sure, then a good starting point seems to be if, like you mentioned, the manager kept track of registered events and was able to provide this info. I'll start thinking about the implications and a potential solution, but most likely won't make significant progress until the start of next week :( Happy to hear if you already have any ideas here.