What is the preferred way of performing non blocking I/O in Ruby?

Question

If say I want to retrieve a web page for parsing, but not block the CPU while the I/O is taking place. Is there something equivalent to Python's Eventlet library?

Answer 1

The best HTTP client library for Ruby is Typhoeus, it can be used to perform multiple HTTP requests in parallel in a non-blocking fashion. There is a blocking and non-blocking interface:

# blocking
response = Typhoeus::Request.get("http://stackoverflow.com/")
puts response.body

# non-blocking
request1 = Typhoeus::Request.new("http://stackoverflow.com/")
request1.on_complete do |response|
  puts response.body
end
request2 = Typhoeus::Request.new("http://stackoverflow.com/questions")
request2.on_complete do |response|
  puts response.body
end
hydra = Typhoeus::Hydra.new
hydra.queue(request1)
hydra.queue(request2)
hydra.run # this call is blocking, though

Another option is em-http-request, which runs on top of EventMachine. It has a completely non-blocking interface:

EventMachine.run do
  request = EventMachine::HttpRequest.new('http://stackoverflow.com/').get
  request.callback do
    puts request.response
    EventMachine.stop
  end
end

There's also an interface for making many requests in parallel, similarly to Typhoeus Hydra.

The downside of em-http-request is that it is tied to EventMachine. EventMachine is an awesome framework in itself, but it's an all-or-nothing deal. You need to write your whole application in an evented/continuation-passing-style fashion, and that has been known to cause brain damage. Typhoeus is much better suited to applications that are not already evented.

Answer 2

I'm not sure what Eventlet does, but Ruby has EventMachine, a library for non-blocking IO (amongst other things).