Stop EM when all iterations are complete

gistfile1.rb

# is there a good pattern for this routine?

EM.synchrony do
  
  size = keys.count
  counter = 0
  
  # check if each iteration was completed
  EM::add_periodic_timer( 2 ) do 
    next unless counter == size
    EM.stop
  end

  EM::Synchrony::FiberIterator.new(keys, 2000).each {|key|
    do_something_with(key).callback { counter += 1; }
  }

end

# why checking each 2 sec? 

EM.synchrony do

  size = keys.count
  counter = 0

  EM::Synchrony::FiberIterator.new(keys, 2000).each {|key|
    # .callback -> counter = +1 -> if counter == size -> EM.stop
    EM.stop if counter == size
    do_something_with(key).callback { counter += 1; }
  }

end

yeah, I tried this pattern at another place too: https://github.com/yankov/redis-migrator/blob/master/migrator.rb#L43.
But the point was that it can be more complicated than just comparing a counter, and counter could be changed from various other places.

Anyways, EM turned out to be not the best approach for this job.