On Wed, 9 Apr 2008, Michael Kerrisk wrote: > On Wed, Apr 9, 2008 at 1:07 PM, Sam Varshavchik <mrsam@xxxxxxxxxxxxxxx> wrote: > > Q2 > > > > Can two epoll sets wait for the same file descriptor? If so, are events > > reported to both epoll file descriptors? > > > > A2 > > > > Yes, and events would be reported to both. However, it is not recommended. > > > > ========= > > > > It's not clear what "not recommended" means. Furthermore, I don't think > > there's anything wrong with two epoll file descriptors waiting for different > > events on the same file descriptor. One's waiting for POLLIN, the other for > > POLLOUT. What's wrong with that? > > Perhaps Davide has some thought to offer here? You can do it. No problem as far as epoll goes. The "recommended" bit was more because it is very easy to get things wrong from an application perspective POV, when doing that. In the case above, first POLLOUT is "almost" always signaled, so you'll receive continuous events over there. Second, if both events shows up at the same time (say in two different threads) and you do not take care of it, you'll end up handling the same fd, at the same time, in two different threads. *Many* users got this wrong, so *many* times, that the "not recommended" is the least warning we can issue. - Davide -- To unsubscribe from this list: send the line "unsubscribe linux-man" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
