Re: [BUG] ob-python hangs on second start [9.5.4 (release_9.5.4-763-g06373a @ ~/emacs/org-mode/lisp/)]

[Jack Kamm]

Ihor Radchenko <yantar92@posteo.net> writes:

> Peter Mao <peter.mao@gmail.com> writes:
>
>> Expectation:  When running ob-python code blocks, I should be able to
>> kill the python session in the *Python* buffer and run another code
>> block (or the same one).
>>
>> Problem:  ob-python works fine on the first execution, but after
>> `exit()`ing the python session, it hangs without executing the code.
>> After a `C-g`, the prompt in the *Python* session shows up, but one then
>> has to re-execute the code block, as none of it has run.
>
> Confirmed.
>
> It looks like `python-shell-first-prompt-hook' does not get triggered
> in the described scenario with exit() and we enter infinite loop in the
> code below.

I think `python-shell-first-prompt-hook' is actually still triggered,
but rather it is `org-babel-comint-wait-for-output' that is hanging
while waiting for startup. However, we can just replace it with a
`sleep-for' instead, because we now wait for
`org-babel-python--initialized' anyways.

See the attached patch. Please let me know if it fixes the problem for
you.

>From d5721aa37a399afcd527906e5d9f1b6bce37fdb9 Mon Sep 17 00:00:00 2001
From: Jack Kamm <jackkamm@gmail.com>
Date: Sun, 27 Aug 2023 14:13:15 -0700
Subject: [PATCH] ob-python: Fix hanging on second start

See: https://list.orgmode.org/87ttsnh5bx.fsf@localhost/T/#t

* lisp/ob-python.el (org-babel-python-initiate-session-by-key): Switch
from `org-babel-comint-wait-for-output' to `sleep-for' while waiting
for `org-babel-python--initialized', to prevent hanging on restarted
Python process.
* testing/lisp/test-ob-python.el (test-ob-python/session-restart): New
test for restarting ob-python session process.
---
 lisp/ob-python.el              |  2 +-
 testing/lisp/test-ob-python.el | 19 +++++++++++++++++++
 2 files changed, 20 insertions(+), 1 deletion(-)

diff --git a/lisp/ob-python.el b/lisp/ob-python.el
index b9dab91b4..6b216ce89 100644
--- a/lisp/ob-python.el
+++ b/lisp/ob-python.el
@@ -272,7 +272,7 @@ (defun org-babel-python-initiate-session-by-key (&optional 
session)
       ;; multiple prompts during initialization.
       (with-current-buffer py-buffer
         (while (not org-babel-python--initialized)
-          (org-babel-comint-wait-for-output py-buffer)))
+          (sleep-for 0 10)))
       (setq org-babel-python-buffers
            (cons (cons session py-buffer)
                  (assq-delete-all session org-babel-python-buffers)))
diff --git a/testing/lisp/test-ob-python.el b/testing/lisp/test-ob-python.el
index 82fbca36e..c11e1d0c2 100644
--- a/testing/lisp/test-ob-python.el
+++ b/testing/lisp/test-ob-python.el
@@ -310,6 +310,25 @@ (ert-deftest test-ob-python/async-local-python-shell ()
 #+end_src"
     (should (org-babel-execute-src-block))))
 
+(ert-deftest test-ob-python/session-restart ()
+  ;; Disable the test on older Emacs as built-in python.el sometimes
+  ;; fail to initialize session.
+  (skip-unless (version<= "28" emacs-version))
+  (should
+   (equal "success"
+          (progn
+            (org-test-with-temp-text "#+begin_src python :session :results 
output
+print('start')
+#+end_src"
+                                    (org-babel-execute-src-block))
+            (let ((proc (python-shell-get-process)))
+              (python-shell-send-string "exit()")
+              (while (accept-process-output proc)))
+            (org-test-with-temp-text "#+begin_src python :session :results 
output
+print('success')
+#+end_src"
+                                    (org-babel-execute-src-block))))))
+
 (provide 'test-ob-python)
 
 ;;; test-ob-python.el ends here
-- 
2.41.0