Gem::RequestSet#install

# File tmp/rubies/ruby-3.1.3/lib/rubygems/request_set.rb, line 145
def install(options, &block) # :yields: request, installer
  if dir = options[:install_dir]
    requests = install_into dir, false, options, &block
    return requests
  end

  @prerelease = options[:prerelease]

  requests = []
  download_queue = Thread::Queue.new

  # Create a thread-safe list of gems to download
  sorted_requests.each do |req|
    download_queue << req
  end

  # Create N threads in a pool, have them download all the gems
  threads = Gem.configuration.concurrent_downloads.times.map do
    # When a thread pops this item, it knows to stop running. The symbol
    # is queued here so that there will be one symbol per thread.
    download_queue << :stop

    Thread.new do
      # The pop method will block waiting for items, so the only way
      # to stop a thread from running is to provide a final item that
      # means the thread should stop.
      while req = download_queue.pop
        break if req == :stop
        req.spec.download options unless req.installed?
      end
    end
  end

  # Wait for all the downloads to finish before continuing
  threads.each(&:value)

  # Install requested gems after they have been downloaded
  sorted_requests.each do |req|
    if req.installed?
      req.spec.spec.build_extensions

      if @always_install.none? {|spec| spec == req.spec.spec }
        yield req, nil if block_given?
        next
      end
    end

    spec =
      begin
        req.spec.install options do |installer|
          yield req, installer if block_given?
        end
      rescue Gem::RuntimeRequirementNotMetError => e
        suggestion = "There are no versions of #{req.request} compatible with your Ruby & RubyGems"
        suggestion += ". Maybe try installing an older version of the gem you're looking for?" unless @always_install.include?(req.spec.spec)
        e.suggestion = suggestion
        raise
      end

    requests << spec
  end

  return requests if options[:gemdeps]

  install_hooks requests, options

  requests
end