Hi -

I maintain libwebsockets (https://libwebsockets.org / https://github.com/warmcat/libwebsockets ). Thanks to user contribution over the years it now supports libuv, libev and libevent.


Libevent was the most recent addition; until then lws supports the idea of building the library with bindings to both libuv and libev, and choose which one to use at runtime. So libevent was added to the happy coexistence merry-go-round.

However now I get a big headache, because both libev and libevent define EV_READ / EV_WRITE, to different things.

libevent says

/usr/include/event2/event.h:#define EV_READ             0x02
/usr/include/event2/event.h:#define EV_WRITE    0x04

and libev says

  EV_READ     =            0x01, /* ev_io detected read will not block */
  EV_WRITE    =            0x02, /* ev_io detected write will not block */

Since libevent uses the preprocessor, it gets the final say; in other words since it defines EV_READ etc to a different value, building some software that can operate with both libevent and libev results in nothing working or not even build completing if you include the libevent bits first.

This is basically an interoperability problem between libevent and libev, or libev and libevent, it would be great if there is something that can be done to allow the happy coexistence merry-go-round to spin once more for these two libraries.

I opened a github issue at

https://github.com/libevent/libevent/issues/596

for libevent, but I learned there the situation is more complex than I expected, with libev providing some libevent compatibility by design.

For downstream maintainers like me whose users wish to be able to use both, and where distro consumers should be able to tick all the boxes and choose at runtime, are there any ideas what can be done to improve the situation?

-Andy

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