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Comment by tptacek | Hacker News Reader

Maybe, but part of the value of async programming is never having to thread, so none of this really lights me up.

Coro basically allows you to write:

   foo();
   bar();

instead of:

   foo( cb => sub { bar() } );

Behind the scenes, it's basically the same thing. It's cooperative so your code does not get preempted where you don't want it to be; the locking is implicit.

But you can switch to preemption and explicit locking if you desire. At that point, IMO, it's time to ditch Perl / Python / Ruby and use a language with a sane STM implementation, because locks suck.

Honest question: is there a purely event-driven I/O framework (no threads anywhere)?

The one that a lot of people have gotten excited about recently is Node.js and that uses threads for file I/O (libeio).

What you you think a "thread" is? A thread of execution? An OS thread? A lightweight thread?

Without defining thread, your question is pretty close to meaningless.

http://github.com/lifo/cramp

It works best in Thin (EventMachine) or Rainbows! (Fibers).

If you are doing I/O you should use NeverBlock (http://www.espace.com.eg/neverblock/) they've even implemented a MySQL driver, the best part is they're 'drop-in' so you don't have to learn a new API, they just hide the async calls from you.

Fibers I think are closer to Erlang style than the event loop, and much more straight forward to program.

> Honest question: is there a purely event-driven I/O framework (no threads anywhere)?

You might look into a continuation-based framework. With continuations, you can do purely event-driven IO written in a direct style: the framework can grab the "callback" itself by snagging the continuation of its slow IO functions.

You still run into the same problems with blocking (non-IO, or non-framework) code taking up more than its fair share of time, however.

EventMachine doesn't thread unless you ask it to. I use EventMachine in Ruby and libevent in C with nary a mutex in sight.

I see. My (wrong) understanding was that EM used a thread pool to do file I/O like Node.js. It appears to add the file descriptor to the event loop's watch list.

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