We write a lot of EventMachine code here; I have some questions. He writes:

EventMachine is • A frankenstein guts the ruby internals • Not in active development • Makes non-blocking IO block • Requires special code from Ruby libraries • Hard to use in an OOP way • Is really difﬁcult to work with • Poorly documented

I'm not sure I understand how EventMachine "guts the Ruby internals" (I didn't watch the talk). It's true that EventMachine's internals are C++, not Ruby; there was originally a reason (again, I think it had to do with green threads) that it was designed this way. I'm not sure I can think of the Ruby functionality that EventMachine changes, or the manner in which EventMachine mucks with the interpreter or its runtime. I'm obviously ready to be corrected, but I'm missing how this impacts me as a programmer. Maybe he's talking about exception handling?

I also wasn't aware EventMachine "wasn't under active development". Because it's just an IO loop. Is libevent in active development? Do I need to be aware of that to use it? The underlying OS capabilities EventMachine maps haven't changed in over a decade. I think I'm actually happy they aren't constantly changing it.

I also don't understand how EventMachine "makes non-blocking block". All EventMachine I/O is nonblocking; it's essentially a select loop.

I also don't understand what special code EventMachine demands from libraries. Maybe he means database libraries? That is, maybe he's referring to the fact that you can't use standard Ruby database libraries that rely on blocking I/O inside an EventMachine loop? I'm wondering, then, what he expected. We wrote a little library (a small part of it is on Github) to do evented Mysql, but we stopped doing that when we realized that Redis evented naturally, and we just hook Mysql up through Redis.

"Hard to use in OOP way" just seems wrong, given that the ~30 evented programs I can find in my codebase directory all seem to be pretty object-oriented. So, that's not so much a question on my part.

Really difficult to work with? I've taught 7 different people EventMachine, in a few hours each. EventMachine is easier than Ruby's native sockets interface, in several specific ways.

I think maybe the issue here isn't so much EventMachine, but the idea of using EventMachine as a substrate for frameworks like Sinatra and Rails. That idea is whack, I agree. Trying to retrofit a full-featured web framework onto an event loop seems like an exercise in futility.

But on the other hand, I've been writing Golang code for the past 2 months, and Golang is militantly anti-event; it doesn't even offer a select primitive! Just alternating read/write on two different sockets seems to demand threads! And what I find is, my programs tend to decompose into handler functions naturally anyways. I try to force myself to write socket code like I did when I was 13, reading a line, parsing it, and writing its response, but that code is brittle and harder to follow than a sane set of handler functions.

So, long story short: I'm not arguing that evented code is the best answer to every problem, or that web frameworks should all be evented, or that actor frameworks aren't useful. It's probably true that a lot of people rushed to event frameworks who shouldn't have done that. But there are problems --- like, backend processing, or proxies, or routers and transformers, or feed processors --- where event loops are the most natural way to express a performant solution.