add em.defer

[kostya]

for outside reactor calculations

[igrigorik]

Hmmm, handy! Are you using this in any production code? It makes sense, but something feels odd about this.. for one, the simple examples will work just fine, but things like thread/fiber local variables and their respective scopes can lead to some very confusing behaviors..

[kostya]

not using this in production, but using pure em.defer and its ok.
it seems would be ok.
little test, this behaviour with sinatra-sinchrony

  get '/sleep' do
    x = y = rand(1000)

    r = EM::Synchrony.defer{
      sleep 0.2
      x += 2
      2
    }

    return halt(500) if r != 2
    return halt(500) if x != y + 2

    "OK"
  end

ab -n 1000 -c 1000 not any 500.

Or you mean combinations defer + another synchrony calls?
But maybe would be some confusions with exceptions.

[igrigorik]

We already have a similar / confusing barrier with async iterators, where you need to launch a new fiber within the block. ex: EM::Synchrony.defer { EM::Synchrony.sleep(1) } would crash and burn.

Unfortunately, there is no simple solution for this..

[kostya]

i consider that defer only for long synchronious operations like nokogiri parsing, etc.