[Libevent-users] announcing libev, towards a faster and more featureful libevent

[Christopher Layne]

On Sun, Nov 04, 2007 at 09:37:52PM -0800, Scott Lamb wrote:
> For this program, it's important to know more than that an error has
> occurred. EV_ERROR is totally inadequate. You're using it for several
> different cases. I spotted at least these three:
> 
> * malloc() failed in ev_once - transient runtime error.
> * select() failed with ENOMEM, so libev chose to kill this file
> descriptor and now is notifying userspace.
> * bad file descriptor - probably a logic error.
> 
> What is my program supposed to do? It can't distinguish them, and the
> correct behavior in each of these conditions is totally different. Also,
> in the program I'm thinking of, "libev chose to kill this file
> descriptor" probably means a network link just went down. Ergh.

Great point. It should back away and leave things alone - notifying
to the caller (or whoever else is listening) "this is not acceptable to
me - I suggest you fix it - because I won't" (aka unix way).

> No, on error your library may have muddied the water already by screwing
> with the file descriptors. libevent also makes errors clearer by simply
> returning error from the failed function (I'm thinking of event_once()
> vs ev_once() here.)

Agreed. A library should touch as little as necessary to get the job done.

-cl