use epoll/kqueue/signal-driven IO

There are several problems with that advice:

• They're not available from Perl.
• They'e not POSIX.

  I agree, POSIX is increasingly irrelevant as it isn't a useful representation of *nix any more. (Or for the last two decades for that matter.)

• epoll doesn't work with timers, signals, semaphores, processes, network devices. Not even disk files.

  Yes, there are the calls signalfd(), eventfd(), and timerfd_create(); but they don't help much.

• epoll maybe O(1) for event notifications, but it remains O(n) for modifications to the interest set.

  Fast changing, dynamic descriptor sets require many and frequent calls into the kernel for epoll_ctl(), which gets expensive.

• kqueue addresses most of that, but retains one major flaw in modern systems: Per process interest sets.

  Basically, it hasn't caught up with the advent of the multi-core architectures that are now ubiquitous; which means you can't easily split your loads across those multiple cores by using multiple thread running separate event loops.

  Yes, you can use multiple processes; but that creates the problem of coordination and data sharing between those processes.