"Cannot establish any listening sockets" error precludes autopick: true

[blerner]

Suppose I invoke Headless.run(display: pick-a-display(), autopick: true) do ... end, so that I specify both an initial guess for a display, and ask Headless to handle the rest. My server, for whatever the reason, currently has a particular display that consistently responds with "Cannot establish any listening sockets". (I don't know why; there are no Xvfb processes running at all. But that's beside the point right now...) So if pick-a-display() happens to hit that bad number, then this call to Headless.run will always fail, even though I've asked Headless to autopick a working display.

It seems to me that ensure_xvfb_launched is overly aggressive about terminating the call to :run. It would be nice for pick_available_display do something like

  def pick_available_display(display_set, can_reuse)
    @pending_exception = nil
    display_set.each do |display_number|
      @display = display_number

      return true if xvfb_running? && can_reuse && (xvfb_mine? || !@autopick_display)
      begin
        return true if !xvfb_running? && launch_xvfb
      rescue Headless::Exception => e
        @pending_Exception = e
      end
    end
    raise @pending_exception || Headless::Exception.new("Could not find an available display")
  end

so that if other display options were available, the call would still succeed...