ein-shared-output: Queue up requests ala deferred:$

Try to gracefully handle multiple calls to `ein:shared-output-eval-string' by
wrapping calls to deferred:$. The deferred chain will not call
`ein:cell-execute' if the cell is already running.

Also did a bit of refactoring in ob-ein.

lisp/ein-shared-output.el

@@ -1,3 +1,4 @@
+;; -*- lexical-binding: t -*-
 ;;; ein-shared-output.el --- Output buffer for ein-connect.el
 
 ;; Copyright (C) 2012- Takafumi Arakaki
@@ -216,9 +217,19 @@ shared output buffer.  You can open the buffer by the command
      (list code nil t kernel)))
   (unless kernel (setq kernel (ein:get-kernel-or-error)))
   (let ((cell (ein:shared-output-get-cell)))
-    (apply #'ein:cell-execute cell kernel (ein:trim-indent code) popup args))
-  (when verbose
-    (ein:log 'info "Code \"%s\" is sent to the kernel." code)))
+    ;; If cell is already running, wait until it is finished
+    ;; before executing more code.
+    (deferred:$
+      (deferred:next
+        (deferred:lambda ()
+          (if (not (null (slot-value cell 'running)))
+              (deferred:nextc (deferred:wait 50) self))))
+      (deferred:nextc it
+        (lambda ()
+          (deferred:wait 100) ;; Give everyone a few milliseconds to breath.
+          (apply #'ein:cell-execute cell kernel (ein:trim-indent code) popup args)
+          (when verbose
+            (ein:log 'info "Code \"%s\" is sent to the kernel." code)))))))
 
 
 ;;; Generic getter

lisp/ob-ein.el

@@ -188,21 +188,23 @@ jupyter kernels.
               (org-babel-ein-process-outputs (slot-value cell 'outputs) params)))))
       (deferred:nextc it
         (lambda (formatted-result)
-          (message "Finished deferred ein execution: %s" name)
-          (with-current-buffer buffer
-            (save-excursion
-              (org-babel-goto-named-result name)
-              (search-forward (format "[[ob-ein-async-running: %s]]" name))
-              (replace-match formatted-result)
-              (org-redisplay-inline-images)
-              ;; (when (member "drawer" (cdr (assoc :result-params params)))
-              ;;   ;; open the results drawer
-              ;;   (org-babel-goto-named-result name)
-              ;;   (forward-line)
-              ;; (org-flag-drawer nil))
-              )))))
+          (ein:ob-ein--execute-async-update formatted-result buffer name))))
     (format "[[ob-ein-async-running: %s]]" name)))
 
+(defun ein:ob-ein--execute-async-update (formatted-result buffer name)
+  (message "Finished deferred ein execution: %s" name)
+  (with-current-buffer buffer
+    (save-excursion
+      (org-babel-goto-named-result name)
+      (search-forward (format "[[ob-ein-async-running: %s]]" name))
+      (replace-match formatted-result)
+      (org-redisplay-inline-images)
+      ;; (when (member "drawer" (cdr (assoc :result-params params)))
+      ;;   ;; open the results drawer
+      ;;   (org-babel-goto-named-result name)
+      ;;   (forward-line)
+      ;; (org-flag-drawer nil))
+      )))
 
 (defun ein:ob-ein--execute (full-body session-kernel processed-params)
   (ein:shared-output-eval-string full-body nil nil session-kernel)