def count_open_pipes(pid = Process.pid)
  `lsof -p #{pid} | grep PIPE | wc -l`.to_i
end

uri = 'mongodb://localhost:27017,localhost:27018,localhost:27019/pipes'
NUM_CONNECTIONS = 10
ITERATIONS = 100

ITERATIONS.times do |iter|
  clients = []

  NUM_CONNECTIONS.times do
    client = Mongo::Client.new(uri, database: 'test')
    clients << client
  end

  # Do something (list collections)
  clients.each do |client|
    client.database.collection_names
  end

  # Close clients
  clients.each(&:close)

  puts "Iteration #{iter+1}: Open pipes: #{count_open_pipes}"
  sleep 0.5
end