Introduce new file and custom variable

* jupyter-server-ioloop-comm.el: New file.

* jupyter-server.el (jupyter-server-use-zmq): New variable.
(jupyter-server-abstract-kcomm): New class.
(jupyter-server-kernel-comm): Inherit from it. This is in preparation of
re-purposing the class in a future commit.

Author: nnicandro

jupyter-server-ioloop-comm.el

@@ -0,0 +1,45 @@
+;;; jupyter-server-ioloop-comm.el --- Async support for Jupyter kernel servers -*- lexical-binding: t -*-
+
+;; Copyright (C) 2020 Nathaniel Nicandro
+
+;; Author: Nathaniel Nicandro <nathanielnicandro@gmail.com>
+;; Created: 11 Mar 2020
+
+;; This program is free software; you can redistribute it and/or
+;; modify it under the terms of the GNU General Public License as
+;; published by the Free Software Foundation; either version 3, or (at
+;; your option) any later version.
+
+;; This program is distributed in the hope that it will be useful, but
+;; WITHOUT ANY WARRANTY; without even the implied warranty of
+;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+;; General Public License for more details.
+
+;; You should have received a copy of the GNU General Public License
+;; along with GNU Emacs; see the file COPYING.  If not, write to the
+;; Free Software Foundation, Inc., 59 Temple Place - Suite 330,
+;; Boston, MA 02111-1307, USA.
+
+;;; Commentary:
+
+;; Async support for Jupyter kernel servers. Requires ZMQ.
+
+;;; Code:
+
+(require 'jupyter-server)
+(require 'jupyter-ioloop-comm)
+(require 'jupyter-server-ioloop)
+
+(defgroup jupyter-server-ioloop-comm nil
+  "Async support for Jupyter kernel servers (requires ZMQ)."
+  :group 'jupyter)
+
+(defclass jupyter-server-ioloop-comm (jupyter-server jupyter-ioloop-comm)
+  ())
+
+(defclass jupyter-server-ioloop-kernel-comm (jupyter-server-abstract-kcomm)
+  ())
+
+(provide 'jupyter-server-ioloop-comm)
+
+;;; jupyter-server-ioloop-comm.el ends here

jupyter-server.el

@@ -88,6 +88,11 @@
   "Support for the Jupyter kernel gateway"
   :group 'jupyter)
 
+(defcustom jupyter-server-use-zmq (and (locate-library "zmq") t)
+  "Whether or not ZMQ should be used as a backend."
+  :type 'boolean
+  :group 'jupyter)
+
 (defvar-local jupyter-current-server nil
   "The `jupyter-server' associated with the current buffer.
 Used in, e.g. a `jupyter-server-kernel-list-mode' buffer.")
@@ -159,8 +164,12 @@ Access should be done through `jupyter-available-kernelspecs'.")))
   ;; The notebook server already takes care of forcing shutdown of a kernel.
   (ignore))
 
-(defclass jupyter-server-kernel-comm (jupyter-comm-layer)
-  ((kernel :type jupyter-server-kernel :initarg :kernel)))
+(defclass jupyter-server-abstract-kcomm (jupyter-comm-layer)
+  ((kernel :type jupyter-server-kernel :initarg :kernel))
+  :abstract t)
+
+(defclass jupyter-server-kernel-comm (jupyter-server-abstract-kcomm)
+  ())
 
 (cl-defmethod jupyter-comm-id ((comm jupyter-server-kernel-comm))
   (let* ((kernel (oref comm kernel))