An example HTTP gem connection pool extracted from some of my code for #ruby IRC

connection.rb

@executor = Concurrent::ThreadPoolExecutor.new min_threads: min_threads,
                                               max_threads: max_threads

def connection_pool
  @connection_pool ||= ConnectionPool.new size: @pool_size, timeout: @pool_timeout do
    HTTP.auth("Bearer #{access_token}")
        .persistent(HOST)
        .timeout(@http_timeout)
        .headers(accept_encoding: ACCEPT_ENCODING)
        .use(:auto_inflate)
  end
end
alias connect connection_pool

def disconnect
  @connection_pool&.shutdown(&:close)
  @connection_pool = nil
end

def future(&block)
  Concurrent::Future.execute executor: @executor do
    connection_pool.with(&block)
  end.value
end