CircleCI::Parallel

gem 'circleci-parallel'

# test.rb
require 'circleci/parallel'

CircleCI::Parallel.configure do |config|
  # This hook will be invoked on every node.
  # The current working directory in this hook is set to the local data directory
  # where node specific data should be saved in.
  config.on_every_node.before_sync do
    data = { 'foo' => ENV['CIRCLE_NODE_INDEX'].to_i * 10 }
    json = JSON.generate(data)
    File.write('data.json', json)
  end

  # This hook will be invoked only on the master node after downloading all data from slave nodes.
  # The current working directory in this hook is set to the download data directory
  # where all node data are gathered into.
  # The directory structure on the master node will be the following:
  #
  #     .
  #     ├── node0
  #     │   └── node_specific_data_you_saved_on_node0.txt
  #     ├── node1
  #     │   └── node_specific_data_you_saved_on_node1.txt
  #     └── node2
  #         └── node_specific_data_you_saved_on_node2.txt
  config.on_master_node.after_download do
    merged_data = {}

    Dir.glob('*/data.json') do |path|
      json = File.read(path)
      data = JSON.parse(json)
      node_name = File.dirname(path)
      merged_data[node_name] = data
    end

    p merged_data
    # {
    #   "node0" => { "foo" => 0 },
    #   "node1" => { "foo" => 10 },
    #   "node2" => { "foo" => 20 }
    # }
  end
end

# Sync all nodes in the same build and gather all node data into the master node.
# Invoking this method blocks until the sync and the data transfer is complete.
CircleCI::Parallel.sync