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[PATCH] Async session eval (2nd attempt)

From: Jack Kamm
Subject: [PATCH] Async session eval (2nd attempt)
Date: Sun, 25 Oct 2020 11:54:09 -0700

This patch adds asynchronous evaluation for session blocks in
Python. It also adds functionality to implement async session eval for
other languages using ob-comint.el.

To test the attached patch, add ":async" to a Python session block
with a long computation (or "time.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 prefer to use the built-in
org-babel languages without jupyter.

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.

This is my 2nd attempt at this patch [0]. I have also ported it to an
external package [1], but would like to have this functionality in Org
proper, to permit better code reuse between async and sync
implementations. The external package also includes an R
implementation that I regularly use, as well as a Ruby implementation,
but I've left these out to keep this initial patch smaller, and also I
need to confirm copyright assignment on the Ruby implementation which
was externally contributed.

[1] https://github.com/jackkamm/ob-session-async

>From 8b7695a148d1831c916737650e115833cb7fc752 Mon Sep 17 00:00:00 2001
From: Jack Kamm <jackkamm@gmail.com>
Date: Sun, 25 Oct 2020 11:40:10 -0700
Subject: [PATCH] ob-comint.el, ob-python.el: Async session evaluation

Adds functionality to ob-comint.el to implement async session eval on
a per-language basis.  Adds a reference implementation for ob-python.

* lisp/ob-comint.el (org-babel-comint-with-output): Remove comment.
(org-babel-comint-async-indicator, org-babel-comint-async-buffers,
org-babel-comint-async-dangling): Add buffer-local variables used for
async comint evaluation.
(org-babel-comint-use-async): Add function to determine whether block
should be evaluated asynchronously.
(org-babel-comint-async-filter): Add filter function to attach to
comint-output-filter-functions for babel async eval.
(org-babel-comint-async-register): Add function to setup buffer
variables and hooks for session eval.
(org-babel-comint-async-delete-dangling-and-eval): Add helper function
for async session eval.

* lisp/ob-python.el (org-babel-execute:python): Check for async header
(org-babel-python-evaluate): Check whether to use async evaluation.
(org-babel-python-async-indicator): Add constant for indicating the
start/end of async evaluations.
(org-babel-python-async-evaluate-session): Add function for Python
async eval.

testing/lisp/test-ob-python.el (test-ob-python/async-simple-session-output):
Unit test for Python async session eval.
(test-ob-python/async-named-output): Unit test that Python async eval
can replace named output.
(test-ob-python/async-output-drawer): Unit test that Python async eval
works with drawer results.
 etc/ORG-NEWS                   |  15 +++
 lisp/ob-comint.el              | 172 +++++++++++++++++++++++++++++++--
 lisp/ob-python.el              |  56 ++++++++++-
 testing/lisp/test-ob-python.el |  61 ++++++++++++
 4 files changed, 294 insertions(+), 10 deletions(-)

diff --git a/etc/ORG-NEWS b/etc/ORG-NEWS
index 7f935bf52..9d5fbbe30 100644
--- a/etc/ORG-NEWS
+++ b/etc/ORG-NEWS
@@ -88,6 +88,21 @@ package, to convert pandas Dataframes into orgmode tables:
 | 2 | 3 | 6 |
+*** Async session evaluation
+The =:async= header argument can be used for asynchronous evaluation
+in session blocks for certain languages.
+Currently, async evaluation is supported in Python.  There is also
+functionality to implement async evaluation in other languages that
+use comint, but this needs to be done on a per-language basis.
+By default, async evaluation is disabled unless the =:async= header
+argument is present.  You can also set =:async no= to force it off
+(for example if you've set =:async= in a property drawer).
+Async evaluation is disabled during export.
 * Version 9.4
 ** Incompatible changes
 *** Possibly broken internal file links: please check and fix
diff --git a/lisp/ob-comint.el b/lisp/ob-comint.el
index d3484bb7c..591754dac 100644
--- a/lisp/ob-comint.el
+++ b/lisp/ob-comint.el
@@ -94,12 +94,7 @@ (defmacro org-babel-comint-with-output (meta &rest body)
                               (regexp-quote ,eoe-indicator) nil t)
                               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 +144,171 @@ (defun org-babel-comint-eval-invisibly-and-wait-for-file
    (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 function to clean Babel async output results before insertion.
+Its single argument is a string consisting of output from the
+comint process. It should return a string that will be be passed
+to `org-babel-insert-result'.")
+(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-use-async (params)
+  "Determine whether to use session async evaluation.
+PARAMS are the header arguments as passed to
+  (let ((async (assq :async params))
+        (session (assq :session params)))
+    (and async
+        (not org-babel-exp-reference-buffer)
+         (not (equal (cdr async) "no"))
+         (not (equal (cdr session) "none")))))
+(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)
+                             (let* ((info (org-babel-get-src-block-info))
+                                    (params (nth 2 info))
+                                    (result-params
+                                     (cdr (assq :result-params params))))
+                               (org-babel-insert-result
+                                 (funcall file-callback
+                                          (nth
+                                           2 (org-babel-get-src-block-info))
+                                          tmp-file)
+                                result-params info))
+                            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 beginning of indicator
+                     (- (match-beginning 0) 1)
+                    ;; 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 (+ 1 (match-end 0)))))
+                  ;; Apply callback to clean up the result
+                  (res-str (funcall org-babel-comint-async-chunk-callback
+                                     res-str-raw)))
+             ;; 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)
+                                (let* ((info (org-babel-get-src-block-info))
+                                       (params (nth 2 info))
+                                       (result-params
+                                        (cdr (assq :result-params params))))
+                                 (org-babel-insert-result
+                                   res-str result-params info))
+                               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
+  (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-async-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)
 ;;; ob-comint.el ends here
diff --git a/lisp/ob-python.el b/lisp/ob-python.el
index 6752adc17..e26c34b64 100644
--- a/lisp/ob-python.el
+++ b/lisp/ob-python.el
@@ -84,6 +84,7 @@ (defun org-babel-execute:python (body params)
         (return-val (when (eq result-type 'value)
                       (cdr (assq :return params))))
         (preamble (cdr (assq :preamble params)))
+        (async (org-babel-comint-use-async params))
@@ -92,7 +93,8 @@ (defun org-babel-execute:python (body params)
           (when return-val
             (format (if session "\n%s" "\nreturn %s") return-val))))
          (result (org-babel-python-evaluate
-                 session full-body result-type result-params preamble)))
+                 session full-body result-type
+                 result-params preamble async)))
      (org-babel-pick-name (cdr (assq :colname-names params))
@@ -278,11 +280,14 @@ (defun org-babel-python-format-session-value
          (if (member "pp" result-params) "True" "False")))
 (defun org-babel-python-evaluate
-  (session body &optional result-type result-params preamble)
+  (session body &optional result-type result-params preamble async)
   "Evaluate BODY as Python code."
   (if session
-      (org-babel-python-evaluate-session
-       session body result-type result-params)
+      (if async
+         (org-babel-python-async-evaluate-session
+          session body result-type result-params)
+       (org-babel-python-evaluate-session
+        session body result-type result-params))
      body result-type result-params preamble)))
@@ -391,6 +396,49 @@ (defun org-babel-python-read-string (string)
       (substring string 1 -1)
+;; Async session eval
+(defconst org-babel-python-async-indicator "print 
+(defun org-babel-python-async-value-callback (params tmp-file)
+  (let ((result-params (cdr (assq :result-params params)))
+       (results (org-babel-eval-read-file tmp-file)))
+    (org-babel-result-cond result-params
+      results
+      (org-babel-python-table-or-string results))))
+(defun org-babel-python-async-evaluate-session
+    (session body &optional result-type result-params)
+  "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)
+   "ob_comint_async_python_\\(.+\\)_\\(.+\\)"
+   'org-babel-chomp 'org-babel-python-async-value-callback)
+  (let ((python-shell-buffer-name (org-babel-python-without-earmuffs session)))
+    (pcase result-type
+      (`output
+       (let ((uuid (md5 (number-to-string (random 100000000)))))
+         (with-temp-buffer
+           (insert (format org-babel-python-async-indicator "start" uuid))
+           (insert "\n")
+           (insert body)
+           (insert "\n")
+           (insert (format org-babel-python-async-indicator "end" uuid))
+           (python-shell-send-buffer))
+         uuid))
+      (`value
+       (let ((tmp-results-file (org-babel-temp-file "python-"))
+             (tmp-src-file (org-babel-temp-file "python-")))
+         (with-temp-file tmp-src-file (insert body))
+         (with-temp-buffer
+           (insert (org-babel-python-format-session-value tmp-src-file 
tmp-results-file result-params))
+           (insert "\n")
+           (insert (format org-babel-python-async-indicator "file" 
+           (python-shell-send-buffer))
+         tmp-results-file)))))
 (provide 'ob-python)
 ;;; ob-python.el ends here
diff --git a/testing/lisp/test-ob-python.el b/testing/lisp/test-ob-python.el
index a2cc7b79c..0267678cd 100644
--- a/testing/lisp/test-ob-python.el
+++ b/testing/lisp/test-ob-python.el
@@ -207,6 +207,67 @@ (ert-deftest test-ob-python/session-value-sleep ()
+(ert-deftest test-ob-python/async-simple-session-output ()
+  (let ((org-babel-temporary-directory "/tmp")
+        (org-confirm-babel-evaluate nil))
+    (org-test-with-temp-text
+     "#+begin_src python :session :async yes :results output
+import time
+     (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-python/async-named-output ()
+  (let (org-confirm-babel-evaluate
+        (org-babel-temporary-directory "/tmp")
+        (src-block "#+begin_src python :async :session :results output
+        (results-before "
+#+NAME: foobar
+: Nope!")
+        (results-after "
+#+NAME: foobar
+: Yep!
+    (org-test-with-temp-text
+     (concat src-block results-before)
+     (should (progn (org-babel-execute-src-block)
+                    (sleep-for 0 200)
+                    (string= (concat src-block results-after)
+                             (buffer-string)))))))
+(ert-deftest test-ob-python/async-output-drawer ()
+  (let (org-confirm-babel-evaluate
+        (org-babel-temporary-directory "/tmp")
+        (src-block "#+begin_src python :async :session :results output drawer
+        (result "
+[0, 1, 2]
+    (org-test-with-temp-text
+     src-block
+     (should (progn (org-babel-execute-src-block)
+                    (sleep-for 0 200)
+                    (string= (concat src-block result)
+                             (buffer-string)))))))
 (provide 'test-ob-python)
 ;;; test-ob-python.el ends here

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