[bascule]

> I'm not sure I understand how EventMachine "guts the Ruby internals"

EventMachine does not use the Ruby IO primitives (e.g. TCPSocket, UDPSocket, etc) as the basis of its IO abstraction, and instead has reimplemented its own set of primitives for doing IO.

Because of this it can't take advantage of work being done in Ruby core to advance Ruby's socket layer. For this reason IPv6 support langered, among other problems.

This also severely complicates making multiple implementations of the EventMachine API, such as its JRuby backend (which maps onto Java NIO)

I think the real problem is EventMachine's original goal was to be a cross-language I/O backend similar to libevent or libev, but since it wasn't a particularly good one, the only language that wound up using it was Ruby. Compare to Twisted, which is built on libevent, or to Node, which is built on libev/libuv

[gnufied]

Author of Packet (https://github.com/gnufied/packet) a Reactor library that did use Ruby IO primitives here. I wrote this before, eventmachine had pure Ruby reactor. Non blocking calls were introduced in Ruby 1.8.5 IIRC and my library made heavy use of them, and they were buggy. Some issues I found:

* select() call used to segfault. * the non blocking read/write behaved very differently under different OSes and I am not talking Windows. There were differences between Linux and OSX for example. * Again frequent crashes when reading/writing when nonblock flag is set.

I am sure, situation is lot better now but for building a reactor library, native Ruby IO primitives fell short. There is always lack of advanced selectors (Epoll/KQueue) as well.

Now as I replied to thomas(?) below and since you yourself have wrapped libevent for Ruby 1.9, there were severe limitation in interpreter back then for even libevent wrapper to work. So I guess, given historical reasons, it made sense Eventmachine did not use native Ruby IO primitives or libevent.

[tptacek]

I like libevent and all, but I don't think Twisted's use of libevent is a particularly big win for Twisted.

Again, this is apocryphal, but I remember someone trying to wrap Ruby around libevent and failing; I remember there being a reason this had to be done bespoke. And having fallen into this particular NIH trap many times before: there's just not a whole lot to a simple socket I/O loop.

What's been your experience with JRuby/EventMachine?

[gnufied]

Zed shaw tried to make libevent work with Ruby, but this was when we had Ruby 1.8.5 and there were problems with Ruby interpreter that prevented this (around threading IIRC).

[bascule]

For what it's worth, I've done two libev bindings, rev/Cool.io (originally in 2008) and nio4r in 2011

[cdavid]

At least 2 years ago, twisted did not use libevent, it was mostly pure python except for a very tiny piece of code (and optional stuff of course).

I am sure you could write a libevent-based reactor, but twisted was started a long time ago (10 years ? The twisted book in o'Reilly was published in 2005), before libevent existed I think.

[tptacek]

No, libevent existed before Twisted; its first release was in 2000, and we used it extensively at Arbor Networks just a couple years later.

[cdavid]

Thanks for the correction. Seems that I confused the dates with libev that came after.

[draegtun]

> ... Compare to Twisted, which is built on libevent, or to Node, which is built on libev/libuv

Or compared to AnyEvent which works with [m]any event loop - https://metacpan.org/module/AnyEvent