problem with recursive nested iterator

[francescoagati]

with this code

require 'rubygems' require 'eventmachine' require "em-synchrony" require "em-synchrony/em-http" require "em-synchrony/iterator" require 'nokogiri'

EM.synchrony do concurrency = 2 urls = ["http://www.x1.com", "http://www.x2.com"]

iterator will execute async blocks until completion, .each, .inject also work!

results = EM::Synchrony::Iterator.new(urls, concurrency).map do |url, iter|

# fire async requests, on completion advance the iterator
http = EventMachine::HttpRequest.new(url).aget
http.callback { iter.return(http) }

end

result2 = EM::Synchrony::Iterator.new(results, concurrency).map do |client, iter| doc=Nokogiri::XML(client.response)

results_xml=nil
Fiber.new do

  results_xml = EM::Synchrony::Iterator.new(doc.search("*"), concurrency).map do |node, iter2|
    iter2.return(node.name)
  end

end.resume

iter.return(results_xml)

end

p result2

EventMachine.stop end

result2 is an array of nil. if like if second iterator don't return to first iterator the result. where i have write wrong code? is right or synchroni can only use of one level of profondity in stack?

[igrigorik]

Francesco, you don't necessarily have to use synchrony iterators for every operation. Specifically, you only need to use them when you're making an outbound network call, which may block for a long time.

In your example, once you've fetched the page, simply iterate over the results using your regular ruby each/map/collect/inject. You don't win anything by wrapping your code into more fibers there, since all of those operations are CPU bound.

Here's a simplified, working example of the code you provided: https://gist.github.com/735865

[francescoagati]

ok thanks in advance.