class Bundler::Installer

def install_in_parallel(size, standalone)
  name2spec = {}
  remains = {}
  enqueued = {}
  specs.each do |spec|
    name2spec[spec.name] = spec
    remains[spec.name] = true
  end
  worker_pool = ParallelWorkers.worker_pool size, lambda { |name, worker|
    spec = name2spec[name]
    message = install_gem_from_spec spec, standalone, worker
    { :name => spec.name, :post_install => message }
  }
  # Keys in the remains hash represent uninstalled gems specs.
  # We enqueue all gem specs that do not have any dependencies.
  # Later we call this lambda again to install specs that depended on
  # previously installed specifications. We continue until all specs
  # are installed.
  enqueue_remaining_specs = lambda do
    remains.keys.each do |name|
      next if enqueued[name]
      spec = name2spec[name]
      if ready_to_install?(spec, remains)
        worker_pool.enq name
        enqueued[name] = true
      end
    end
  end
  enqueue_remaining_specs.call
  until remains.empty?
    message = worker_pool.deq
    remains.delete message[:name]
    if message[:post_install]
      Installer.post_install_messages[message[:name]] = message[:post_install]
    end
    enqueue_remaining_specs.call
  end
  message
ensure
  worker_pool && worker_pool.stop
end