Asynchronous session evaluation

Asynchronous session evaluation

[Jack Kamm]

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For some time I've been wishing for asynchronous Babel session
evaluation. So I've created an experimental branch implementing this. I
have an initial version working for R, so I thought it'd be a good time
to seek feedback and gauge interest.

To test the attached patch, add ":async yes" to an R session block
with a long computation (or "System.sleep") in it. Upon evaluation,
your Emacs won't freeze to wait for the result -- instead, a
placeholder will be inserted, and replaced with the true result when
it's ready.

I'll note how this is different from some related projects. ob-async
implements asynchronous evaluation for Babel, but it doesn't work with
sessions. emacs-jupyter, ein, and ob-ipython all implement asynchronous
session evaluation, but only for Jupyter kernels. Jupyter is great for
some cases, but sometimes I'd prefer not to use it. For example, the
native R console has great Emacs support via ESS, whereas the Jupyter R
console doesn't work with ESS and is not widely used in the R community.

Note that if you use ob-async, make sure to add "R" to
`ob-async-no-async-languages-alist' before testing this.

The new functionality is mainly implemented in
`org-babel-comint-async-filter', which I've defined in ob-comint.el,
and added as a hook to `comint-output-filter-functions'.  Whenever new
output is added to the comint buffer, the filter scans for an
indicator token (this is inspired by
`org-babel-comint-with-output'). Upon encountering the token, the
filter uses a regular expression to extract a UUID or temp-file
associated with the result, then searches for the appropriate location
to add the result to.

I've tried to make behavior as similar as possible to existing
ob-comint behavior, so that some of the existing code for interacting
with ob-comint can be refactored and reused. Still, it will be a large
task to add this feature for all languages. So far, I've only done R,
but my thought is to implement a few more languages before nailing
down the functionality. But, I hope something like this could be
merged in supporting just a subset of languages initially, then
gradually increasing the number of supported languages over time.


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From f1c198a85666507164e9a97a7e0758f1d5dcf126 Mon Sep 17 00:00:00 2001
From: Jack Kamm <jackkamm@gmail.com>
Date: Sat, 1 Jun 2019 12:26:13 -0700
Subject: [PATCH] Add asynchronous Babel comint & R eval

---
 lisp/ob-R.el              | 174 +++++++++++++++++++++++++++++---------
 lisp/ob-comint.el         | 152 +++++++++++++++++++++++++++++++--
 testing/lisp/test-ob-R.el |  24 ++++++
 3 files changed, 305 insertions(+), 45 deletions(-)

diff --git a/lisp/ob-R.el b/lisp/ob-R.el
index 9e738a8a5..74336d083 100644
--- a/lisp/ob-R.el
+++ b/lisp/ob-R.el
@@ -161,8 +161,8 @@ This function is called by `org-babel-execute-src-block'."
 		     (cdr (assq :session params)) params))
 	   (graphics-file (and (member "graphics" (assq :result-params params))
 			       (org-babel-graphical-output-file params)))
-	   (colnames-p (unless graphics-file (cdr (assq :colnames params))))
 	   (rownames-p (unless graphics-file (cdr (assq :rownames params))))
+	   (async (cdr (assq :async params)))
 	   (full-body
 	    (let ((inside
 		   (list (org-babel-expand-body:R body params graphics-file))))
@@ -178,12 +178,11 @@ This function is called by `org-babel-execute-src-block'."
 	   (result
 	    (org-babel-R-evaluate
 	     session full-body result-type result-params
-	     (or (equal "yes" colnames-p)
-		 (org-babel-pick-name
-		  (cdr (assq :colname-names params)) colnames-p))
+	     (org-babel-R-get-colnames-p params)
 	     (or (equal "yes" rownames-p)
 		 (org-babel-pick-name
-		  (cdr (assq :rowname-names params)) rownames-p)))))
+		  (cdr (assq :rowname-names params)) rownames-p))
+	     (equal "yes" async))))
       (if graphics-file nil result))))
 
 (defun org-babel-prep-session:R (session params)
@@ -369,11 +368,15 @@ Has four %s escapes to be filled in:
 4. The name of the file to write to")
 
 (defun org-babel-R-evaluate
-  (session body result-type result-params column-names-p row-names-p)
+    (session body result-type result-params
+	     column-names-p row-names-p async-p)
   "Evaluate R code in BODY."
   (if session
-      (org-babel-R-evaluate-session
-       session body result-type result-params column-names-p row-names-p)
+      (if async-p
+	  (org-babel-R-evaluate-session-async
+	   session body result-type column-names-p row-names-p)
+	(org-babel-R-evaluate-session
+	 session body result-type result-params column-names-p row-names-p))
     (org-babel-R-evaluate-external-process
      body result-type result-params column-names-p row-names-p)))
 
@@ -395,11 +398,7 @@ last statement in BODY, as elisp."
 			       (format "{function ()\n{\n%s\n}}()" body)
 			       (org-babel-process-file-name tmp-file 'noquote)))
        (org-babel-R-process-value-result
-	(org-babel-result-cond result-params
-	  (with-temp-buffer
-	    (insert-file-contents tmp-file)
-	    (org-babel-chomp (buffer-string) "\n"))
-	  (org-babel-import-elisp-from-file tmp-file '(16)))
+	(org-babel-R-value-from-tmp-file result-params tmp-file)
 	column-names-p)))
     (output (org-babel-eval org-babel-R-command body))))
 
@@ -422,38 +421,22 @@ last statement in BODY, as elisp."
      (let ((tmp-file (org-babel-temp-file "R-")))
        (org-babel-comint-eval-invisibly-and-wait-for-file
 	session tmp-file
-	(format org-babel-R-write-object-command
-		(if row-names-p "TRUE" "FALSE")
-		(if column-names-p
-		    (if row-names-p "NA" "TRUE")
-		  "FALSE")
-		".Last.value" (org-babel-process-file-name tmp-file 'noquote)))
+	(org-babel-R-write-last-value-command row-names-p
+					      column-names-p
+					      tmp-file))
        (org-babel-R-process-value-result
-	(org-babel-result-cond result-params
-	  (with-temp-buffer
-	    (insert-file-contents tmp-file)
-	    (org-babel-chomp (buffer-string) "\n"))
-	  (org-babel-import-elisp-from-file tmp-file '(16)))
+	(org-babel-R-value-from-tmp-file result-params tmp-file)
 	column-names-p)))
     (output
      (mapconcat
       'org-babel-chomp
       (butlast
-       (delq nil
-	     (mapcar
-	      (lambda (line) (when (> (length line) 0) line))
-	      (mapcar
-	       (lambda (line) ;; cleanup extra prompts left in output
-		 (if (string-match
-		      "^\\([>+.]\\([ ][>.+]\\)*[ ]\\)"
-		      (car (split-string line "\n")))
-		     (substring line (match-end 1))
-		   line))
-	       (org-babel-comint-with-output (session org-babel-R-eoe-output)
-		 (insert (mapconcat 'org-babel-chomp
-				    (list body org-babel-R-eoe-indicator)
-				    "\n"))
-		 (inferior-ess-send-input)))))) "\n"))))
+       (org-babel-R-clean-session-output
+	(org-babel-comint-with-output (session org-babel-R-eoe-output)
+	  (insert (mapconcat 'org-babel-chomp
+			     (list body org-babel-R-eoe-indicator)
+			     "\n"))
+	  (inferior-ess-send-input)))) "\n"))))
 
 (defun org-babel-R-process-value-result (result column-names-p)
   "R-specific processing of return value.
@@ -462,6 +445,119 @@ Insert hline if column names in output have been requested."
       (cons (car result) (cons 'hline (cdr result)))
     result))
 
+(defun org-babel-R-value-from-tmp-file (result-params tmp-file)
+  "Insert result from TMP-FILE with RESULT-PARAMS."
+  (org-babel-result-cond result-params
+	  (with-temp-buffer
+	    (insert-file-contents tmp-file)
+	    (org-babel-chomp (buffer-string) "\n"))
+	  (org-babel-import-elisp-from-file tmp-file '(16))))
+
+(defun org-babel-R-clean-session-output (output)
+  "Remove extra prompts and empty lines from OUTPUT."
+  (delq nil
+	(mapcar
+	 (lambda (line) (when (> (length line) 0) line))
+	 (mapcar
+	  (lambda (line) ;; cleanup extra prompts left in output
+	    (if (string-match
+		 "^\\([>+.]\\([ ][>.+]\\)*[ ]\\)"
+		 (car (split-string line "\n")))
+		(substring line (match-end 1))
+	      line))
+	  output))))
+
+(defun org-babel-R-write-last-value-command (row-names-p column-names-p tmp-file)
+  "Generate R command to output last value to TMP-FILE."
+  (format org-babel-R-write-object-command
+	  (if row-names-p "TRUE" "FALSE")
+	  (if column-names-p
+	      (if row-names-p "NA" "TRUE")
+	    "FALSE")
+	  ".Last.value" (org-babel-process-file-name tmp-file 'noquote)))
+
+(defun org-babel-R-get-colnames-p (params)
+  "Determine whether to use column names from PARAMS of R Babel block."
+  (let* ((graphics-file (and (member "graphics" (assq :result-params params))
+			     (org-babel-graphical-output-file params)))
+	 (colnames-p (unless graphics-file (cdr (assq :colnames params)))))
+    (or (equal "yes" colnames-p)
+	(org-babel-pick-name
+	 (cdr (assq :colname-names params)) colnames-p))))
+
+;; Async evaluation
+
+(defconst org-babel-R-async-indicator "'org_babel_R_async_%s_%s'")
+(defconst org-babel-R-async-indicator-output
+  "^\\[1\\] \"org_babel_R_async_\\(.+\\)_\\(.+\\)\"$")
+
+(defun org-babel-R-evaluate-session-async
+    (session body result-type column-names-p row-names-p)
+  "Asynchronously evaluate BODY in SESSION.
+Returns a placeholder string for insertion, to later be replaced
+by `org-babel-comint-async-filter'."
+  (org-babel-comint-async-register session (current-buffer)
+				   org-babel-R-async-indicator-output
+				   'org-babel-R-async-output-callback
+				   'org-babel-R-async-value-callback)
+  (cl-case result-type
+    (value
+     (let ((tmp-file (org-babel-temp-file "R-")))
+       (with-temp-buffer
+       (insert
+	(org-babel-chomp body))
+       (let ((ess-local-process-name
+	      (process-name (get-buffer-process session)))
+	     (ess-eval-visibly-p nil))
+	 (ess-eval-buffer nil)))
+       (with-temp-buffer
+	 (insert
+	  (mapconcat 'org-babel-chomp
+		     (list (org-babel-R-write-last-value-command row-names-p
+								 column-names-p
+								 tmp-file)
+			   (format org-babel-R-async-indicator
+				   "file" tmp-file))
+		     "\n"))
+	 (let ((ess-local-process-name
+		(process-name (get-buffer-process session)))
+	       (ess-eval-visibly-p nil))
+	   (ess-eval-buffer nil)))
+       tmp-file))
+    (output
+     (let ((uuid (md5 (number-to-string (random 100000000)))))
+       (org-babel-comint-delete-dangling-and-eval
+	   session
+	 (insert (mapconcat 'org-babel-chomp
+			    (list (format org-babel-R-async-indicator
+					  "start" uuid)
+				  body
+				  (format org-babel-R-async-indicator
+					  "end" uuid))
+			    "\n"))
+	 (inferior-ess-send-input))
+       uuid))))
+
+(defun org-babel-R-async-output-callback (output)
+  "Callback for async output results.
+Assigned locally to `org-babel-comint-async-chunk-callback' in R
+comint buffers used for asynchronous Babel evaluation."
+  (mapconcat
+   'org-babel-chomp
+   (cdr (butlast (mapcar (lambda (line) (string-remove-prefix "\n" line))
+			 (org-babel-R-clean-session-output output))))
+   "\n"))
+
+(defun org-babel-R-async-value-callback (params tmp-file)
+  "Callback for async value results.
+Assigned locally to `org-babel-comint-async-file-callback' in R
+comint buffers used for asynchronous Babel evaluation."
+  (org-babel-R-process-value-result
+   (org-babel-R-value-from-tmp-file
+    (assq :result-params params) tmp-file)
+   ;; TODO this is not exactly the same as colnames-p above...
+   (org-babel-R-get-colnames-p params)))
+
 (provide 'ob-R)
 
 
diff --git a/lisp/ob-comint.el b/lisp/ob-comint.el
index aa0d341da..2131f54dd 100644
--- a/lisp/ob-comint.el
+++ b/lisp/ob-comint.el
@@ -94,12 +94,7 @@ or user `keyboard-quit' during execution of body."
 			       (regexp-quote ,eoe-indicator) nil t)
 			      (re-search-forward
 			       comint-prompt-regexp nil t)))))
-	   (accept-process-output (get-buffer-process (current-buffer)))
-	   ;; thought the following this would allow async
-	   ;; background running, but I was wrong...
-	   ;; (run-with-timer .5 .5 'accept-process-output
-	   ;; 		 (get-buffer-process (current-buffer)))
-	   )
+	   (accept-process-output (get-buffer-process (current-buffer))))
 	 ;; replace cut dangling text
 	 (goto-char (process-mark (get-buffer-process (current-buffer))))
 	 (insert dangling-text)
@@ -149,6 +144,151 @@ FILE exists at end of evaluation."
    (if (= (aref string (1- (length string))) ?\n) string (concat string "\n")))
   (while (not (file-exists-p file)) (sit-for (or period 0.25))))
 
+
+;; Async evaluation
+
+(defvar-local org-babel-comint-async-indicator nil
+  "Regular expression that `org-babel-comint-async-filter' scans for.
+It should have 2 parenthesized expressions,
+e.g. \"org_babel_async_\\(start\\|end\\|file\\)_\\(.*\\)\". The
+first parenthesized expression determines whether the token is
+delimiting a result block, or whether the result is in a file. If
+delimiting a block, the second expression gives a UUID for the
+location to insert the result. Otherwise, the result is in a tmp
+file, and the second expression gives the file name.")
+
+(defvar-local org-babel-comint-async-buffers nil
+  "List of org-mode buffers to check for Babel async output results.")
+
+(defvar-local org-babel-comint-async-file-callback nil
+  "Callback to clean and insert Babel async results from a temp file.
+The callback function takes two arguments: the alist of params of the Babel
+source block, and the name of the temp file.")
+
+(defvar-local org-babel-comint-async-chunk-callback nil
+  "Callback to clean Babel async output results before insertion.
+The input is assumed to be split by `comint-prompt-regexp', as in
+ `org-babel-comint-with-output'. The output should be a string.")
+
+(defvar-local org-babel-comint-async-dangling nil
+  "Dangling piece of the last process output, in case
+`org-babel-comint-async-indicator' is spread across multiple
+comint outputs due to buffering.")
+
+(defun org-babel-comint-async-filter (string)
+  "Captures Babel async output from comint buffer back to org-mode buffers.
+This function is added as a hook to `comint-output-filter-functions'.
+STRING contains the output originally inserted into the comint buffer."
+  ;; Remove outdated org-mode buffers
+  (setq org-babel-comint-async-buffers
+	(cl-loop for buf in org-babel-comint-async-buffers
+	      if (buffer-live-p buf)
+	      collect buf))
+  (let* ((indicator org-babel-comint-async-indicator)
+	 (org-buffers org-babel-comint-async-buffers)
+	 (file-callback org-babel-comint-async-file-callback)
+	 (combined-string (concat org-babel-comint-async-dangling string))
+	 (new-dangling combined-string)
+	 ;; list of UUID's matched by `org-babel-comint-async-indicator'
+	 uuid-list)
+    (with-temp-buffer
+      (insert combined-string)
+      (goto-char (point-min))
+      (while (re-search-forward indicator nil t)
+	;; update dangling
+	(setq new-dangling (buffer-substring (point) (point-max)))
+	(cond ((equal (match-string 1) "end")
+	       ;; save UUID for insertion later
+	       (push (match-string 2) uuid-list))
+	      ((equal (match-string 1) "file")
+	       ;; insert results from tmp-file
+	       (let ((tmp-file (match-string 2)))
+		 (cl-loop for buf in org-buffers
+		       until
+		       (with-current-buffer buf
+			 (save-excursion
+			   (goto-char (point-min))
+			   (when (search-forward tmp-file nil t)
+			     (org-babel-previous-src-block)
+			     (org-babel-remove-result)
+			     (org-babel-insert-result
+			      (funcall file-callback
+				       (nth
+					2 (org-babel-get-src-block-info))
+				       tmp-file))
+			     t))))))))
+      ;; Truncate dangling to only the most recent output
+      (when (> (length new-dangling) (length string))
+	(setq new-dangling string)))
+    (setq-local org-babel-comint-async-dangling new-dangling)
+    (when uuid-list
+      ;; Search for results in the comint buffer
+      (save-excursion
+	(goto-char (point-max))
+	(while uuid-list
+	  (re-search-backward indicator)
+	  (when (equal (match-string 1) "end")
+	    (let* ((uuid (match-string-no-properties 2))
+		   (res-str-raw
+		    (buffer-substring
+		     ;; move point to end of indicator
+		     (re-search-forward indicator)
+		     ;; find the matching start indicator
+		     (cl-loop for pos = (re-search-backward indicator)
+			   until (and (equal (match-string 1) "start")
+				      (equal (match-string 2) uuid))
+			   finally return pos)))
+		   ;; Apply callback to clean up the result
+		   (res-str (funcall org-babel-comint-async-chunk-callback
+				     (split-string
+				      res-str-raw
+				      comint-prompt-regexp))))
+	      ;; Search for uuid in associated org-buffers to insert results
+	      (cl-loop for buf in org-buffers
+		    until (with-current-buffer buf
+			    (save-excursion
+			      (goto-char (point-min))
+			      (when (search-forward uuid nil t)
+				(org-babel-previous-src-block)
+				(org-babel-remove-result)
+				(org-babel-insert-result res-str)
+				t))))
+	      ;; Remove uuid from the list to search for
+	      (setq uuid-list (delete uuid uuid-list)))))))))
+
+(defun org-babel-comint-async-register
+    (session-buffer org-buffer indicator-regexp
+		    chunk-callback file-callback)
+  "Sets local org-babel-comint-async variables in SESSION-BUFFER.
+ORG-BUFFER is added to `org-babel-comint-async-buffers' if not
+present.  `org-babel-comint-async-indicator',
+`org-babel-comint-async-chunk-callback', and
+`org-babel-comint-async-file-callback' are set to
+INDICATOR-REGEXP, CHUNK-CALLBACK, and FILE-CALLBACK
+respectively."
+  (org-babel-comint-in-buffer session-buffer
+    (setq org-babel-comint-async-indicator indicator-regexp
+	  org-babel-comint-async-chunk-callback chunk-callback
+	  org-babel-comint-async-file-callback file-callback)
+    (unless (memq org-buffer org-babel-comint-async-buffers)
+      (setq org-babel-comint-async-buffers
+	    (cons org-buffer org-babel-comint-async-buffers)))
+    (add-hook 'comint-output-filter-functions
+	      'org-babel-comint-async-filter nil t)))
+
+(defmacro org-babel-comint-delete-dangling-and-eval
+    (session-buffer &rest body)
+  "Remove dangling text in SESSION-BUFFER and evaluate BODY.
+This is analogous to `org-babel-comint-with-output', but meant
+for asynchronous output, and much shorter because inserting the
+result is delegated to `org-babel-comint-async-filter'."
+  (declare (indent 1))
+  `(org-babel-comint-in-buffer ,session-buffer
+     (goto-char (process-mark (get-buffer-process (current-buffer))))
+     (delete-region (point) (point-max))
+     ,@body))
+(def-edebug-spec org-babel-comint-async-with-output (sexp body))
+
 (provide 'ob-comint)
 
 
diff --git a/testing/lisp/test-ob-R.el b/testing/lisp/test-ob-R.el
index 7ce340ba4..185b211ab 100644
--- a/testing/lisp/test-ob-R.el
+++ b/testing/lisp/test-ob-R.el
@@ -31,6 +31,30 @@
      "#+begin_src R :session R\n  paste(\"Yep!\")\n#+end_src\n"
      (should (string= "Yep!" (org-babel-execute-src-block))))))
 
+(ert-deftest test-ob-R/simple-session-async-value ()
+  (let (ess-ask-for-ess-directory ess-history-file)
+    (org-test-with-temp-text
+     "#+begin_src R :session R :async yes\n  Sys.sleep(.1)\n  paste(\"Yep!\")\n#+end_src\n"
+     (should (let ((expected "Yep!"))
+	       (and (not (string= expected (org-babel-execute-src-block)))
+		    (string= expected
+			     (progn
+			       (sleep-for 0 200)
+			       (goto-char (org-babel-where-is-src-block-result))
+			       (org-babel-read-result)))))))))
+
+(ert-deftest test-ob-R/simple-session-async-output ()
+  (let (ess-ask-for-ess-directory ess-history-file)
+    (org-test-with-temp-text
+     "#+begin_src R :session R :results output :async yes\n  Sys.sleep(.1)\n  1:5\n#+end_src\n"
+     (should (let ((expected "[1] 1 2 3 4 5"))
+	       (and (not (string= expected (org-babel-execute-src-block)))
+		    (string= expected
+			     (progn
+			       (sleep-for 0 200)
+			       (goto-char (org-babel-where-is-src-block-result))
+			       (org-babel-read-result)))))))))
+
 (ert-deftest test-ob-R/colnames-yes-header-argument ()
   (org-test-with-temp-text "#+name: eg
 | col |
-- 
2.21.0

Re: Asynchronous session evaluation

[Nicolas Goaziou]

Hello,

Jack Kamm <jackkamm@gmail.com> writes:

> For some time I've been wishing for asynchronous Babel session
> evaluation. So I've created an experimental branch implementing this. I
> have an initial version working for R, so I thought it'd be a good time
> to seek feedback and gauge interest.
>
> To test the attached patch, add ":async yes" to an R session block
> with a long computation (or "System.sleep") in it. Upon evaluation,
> your Emacs won't freeze to wait for the result -- instead, a
> placeholder will be inserted, and replaced with the true result when
> it's ready.
>
> I'll note how this is different from some related projects. ob-async
> implements asynchronous evaluation for Babel, but it doesn't work with
> sessions. emacs-jupyter, ein, and ob-ipython all implement asynchronous
> session evaluation, but only for Jupyter kernels. Jupyter is great for
> some cases, but sometimes I'd prefer not to use it. For example, the
> native R console has great Emacs support via ESS, whereas the Jupyter R
> console doesn't work with ESS and is not widely used in the R community.
>
> Note that if you use ob-async, make sure to add "R" to
> `ob-async-no-async-languages-alist' before testing this.
>
> The new functionality is mainly implemented in
> `org-babel-comint-async-filter', which I've defined in ob-comint.el,
> and added as a hook to `comint-output-filter-functions'.  Whenever new
> output is added to the comint buffer, the filter scans for an
> indicator token (this is inspired by
> `org-babel-comint-with-output'). Upon encountering the token, the
> filter uses a regular expression to extract a UUID or temp-file
> associated with the result, then searches for the appropriate location
> to add the result to.
>
> I've tried to make behavior as similar as possible to existing
> ob-comint behavior, so that some of the existing code for interacting
> with ob-comint can be refactored and reused. Still, it will be a large
> task to add this feature for all languages. So far, I've only done R,
> but my thought is to implement a few more languages before nailing
> down the functionality. But, I hope something like this could be
> merged in supporting just a subset of languages initially, then
> gradually increasing the number of supported languages over time.

This sound interesting. I hope this is not going to bit-rot while we're
waiting for feedback.

If you think this is stable enough, however, you could simply integrate
in the master branch after Org 9.3 release. It would require an entry in
ORG-NEWS, though.

WDYT?

Regards,

-- 
Nicolas Goaziou

Re: Asynchronous session evaluation

[Jack Kamm]

Hello,

Nicolas Goaziou <mail@nicolasgoaziou.fr> writes:

> This sound interesting. I hope this is not going to bit-rot while we're
> waiting for feedback.

Since my last e-mail, I ported this code to a separate package here:
https://github.com/jackkamm/ob-session-async

I've been slowly ironing out various kinks, and it's robust enough now
that I use it regularly for my day-to-day work. Some recent tweaks need
a little more battle-testing, but it's close to being ready for wider
circulation.

> If you think this is stable enough, however, you could simply integrate
> in the master branch after Org 9.3 release. It would require an entry in
> ORG-NEWS, though.

I think this would be good -- having the code upstream in Org, rather
than as a separate package, will allow for better code reuse, since the
async session evaluation needs to be implemented separately for each language.

I'll start working on porting my updates back into my org-mode branch,
and integrate with master after the 9.3 release. Happy to write an
ORG-NEWS entry as well.

Is there a timeline for when 9.3 will be coming out?

Best,
Jack

Re: Asynchronous session evaluation

[Jack Kamm]

In case any org-babel R users are interested, this package is now
basically ready to use, and I've added a Readme on how to use it:

https://github.com/jackkamm/ob-session-async

I plan to add more languages, and to eventually contribute this
functionality back to org-mode when it's ready.