Utility class to help monitor open file descriptors

file_descriptor_sentry.rb

# Utility class to help monitor open file descriptors
#
class FileDescriptorSentry
  class << self
    # Return a count of all open file descriptors in the current process.
    #
    def count_open_fds
      ObjectSpace.each_object(IO).count { |o| o.respond_to?(:closed?) && !o.closed? rescue false }
    end

    # Execute a block and print a warning on STDERR if any file descriptors are left open.
    #
    def check_open_fds
      before = count_open_fds
      yield
    ensure
      leaked = count_open_fds - before
      $stderr.puts "You left #{leaked} file descriptors open!" if leaked > 0
    end
  end
end