Markdown is not always converted to python in multiprocessing/threading from the Quarto VS Code extension

---
title: "Markdown is not always converted to python in multiprocessing/threading"
format: html
execute:
  enabled: true
jupyter:
  kernelspec:
    display_name: "Python 3"
    language: python
    name: python3
---

## Minimal example

This notebook demonstrates a potential issue with rendering notebooks using `multiprocessing.Manager().Queue()` and `threading.Thread`.

```{python}
from multiprocessing import Manager
from threading import Thread
try:
    from tqdm import tqdm
except ImportError:
    tqdm = None

def update(progress_bar, queue, total):
    """Update progress bar based on values from the queue."""
    for _ in range(total):
        queue.get()
        if progress_bar is not None:
            progress_bar.update(1)

def simulate_issue():
    range_length = 10
    unit = "items"
    
    progress_bar = None if tqdm is None else tqdm(total=range_length, unit=unit)
    queue = Manager().Queue()
    thread = Thread(target=update, args=(progress_bar, queue, range_length))
    thread.start()
    
    for _ in range(range_length):
        queue.put('done')
    
    thread.join()
    if progress_bar is not None:
        progress_bar.close()
```

executing `simulate_issue()` proceeds without error in a jupyter notebook or ipython terminal

```{python}
simulate_issue()
```

but leads to

```pytb
  0%|          | 0/10 [00:00<?, ?items/s]Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "~/.pyenv/versions/3.10.13/lib/python3.10/multiprocessing/spawn.py", line 116, in spawn_main
    exitcode = _main(fd, parent_sentinel)
  File "~/.pyenv/versions/3.10.13/lib/python3.10/multiprocessing/spawn.py", line 125, in _main
    prepare(preparation_data)
  File "~/.pyenv/versions/3.10.13/lib/python3.10/multiprocessing/spawn.py", line 236, in prepare
    _fixup_main_from_path(data['init_main_from_path'])
  File "~/.pyenv/versions/3.10.13/lib/python3.10/multiprocessing/spawn.py", line 287, in _fixup_main_from_path
    main_content = runpy.run_path(main_path,
  File "~/.pyenv/versions/3.10.13/lib/python3.10/runpy.py", line 288, in run_path
    code, fname = _get_code_from_file(run_name, path_name)
  File "~/.pyenv/versions/3.10.13/lib/python3.10/runpy.py", line 257, in _get_code_from_file
    code = compile(f.read(), fname, 'exec')
  File "~/template.qmd", line 1
    ---
       ^
SyntaxError: invalid syntax
```

when executed from the Quarto VS Code extension.

❯ quarto render template.qmd --debug

Starting python3 kernel...Done

Executing 'template.ipynb'
  Cell 1/2: ''...Done
  Cell 2/2: ''...ERROR: 

An error occurred while executing the following cell:
------------------
simulate_issue()
------------------

----- stderr -----
  0%|          | 0/10 [00:00<?, ?items/s]
------------------

---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
Cell In[2], line 1
----> 1 simulate_issue()

Cell In[1], line 20, in simulate_issue()
     17 unit = "items"
     19 progress_bar = None if tqdm is None else tqdm(total=range_length, unit=unit)
---> 20 queue = Manager().Queue()
     21 thread = Thread(target=update, args=(progress_bar, queue, range_length))
     22 thread.start()

File ~/.pyenv/versions/3.10.13/lib/python3.10/multiprocessing/context.py:57, in BaseContext.Manager(self)
     55 from .managers import SyncManager
     56 m = SyncManager(ctx=self.get_context())
---> 57 m.start()
     58 return m

File ~/.pyenv/versions/3.10.13/lib/python3.10/multiprocessing/managers.py:562, in BaseManager.start(self, initializer, initargs)
    560 ident = ':'.join(str(i) for i in self._process._identity)
    561 self._process.name = type(self).__name__  + '-' + ident
--> 562 self._process.start()
    564 # get address of server
    565 writer.close()

File ~/.pyenv/versions/3.10.13/lib/python3.10/multiprocessing/process.py:121, in BaseProcess.start(self)
    118 assert not _current_process._config.get('daemon'), \
    119        'daemonic processes are not allowed to have children'
    120 _cleanup()
--> 121 self._popen = self._Popen(self)
    122 self._sentinel = self._popen.sentinel
    123 # Avoid a refcycle if the target function holds an indirect
    124 # reference to the process object (see bpo-30775)

File ~/.pyenv/versions/3.10.13/lib/python3.10/multiprocessing/context.py:288, in SpawnProcess._Popen(process_obj)
    285 @staticmethod
    286 def _Popen(process_obj):
    287     from .popen_spawn_posix import Popen
--> 288     return Popen(process_obj)

File ~/.pyenv/versions/3.10.13/lib/python3.10/multiprocessing/popen_spawn_posix.py:32, in Popen.__init__(self, process_obj)
     30 def __init__(self, process_obj):
     31     self._fds = []
---> 32     super().__init__(process_obj)

File ~/.pyenv/versions/3.10.13/lib/python3.10/multiprocessing/popen_fork.py:19, in Popen.__init__(self, process_obj)
     17 self.returncode = None
     18 self.finalizer = None
---> 19 self._launch(process_obj)

File ~/.pyenv/versions/3.10.13/lib/python3.10/multiprocessing/popen_spawn_posix.py:42, in Popen._launch(self, process_obj)
     40 tracker_fd = resource_tracker.getfd()
     41 self._fds.append(tracker_fd)
---> 42 prep_data = spawn.get_preparation_data(process_obj._name)
     43 fp = io.BytesIO()
     44 set_spawning_popen(self)

File ~/.pyenv/versions/3.10.13/lib/python3.10/multiprocessing/spawn.py:183, in get_preparation_data(name)
    180 # Figure out whether to initialise main in the subprocess as a module
    181 # or through direct execution (or to leave it alone entirely)
    182 main_module = sys.modules['__main__']
--> 183 main_mod_name = getattr(main_module.__spec__, "name", None)
    184 if main_mod_name is not None:
    185     d['init_main_from_name'] = main_mod_name

AttributeError: module '__main__' has no attribute '__spec__'

❯ code --version                         
1.87.2
863d2581ecda6849923a2118d93a088b0745d9d6
arm64

❯ uname -a                               
Darwin 22.6.0 Darwin Kernel Version 22.6.0: Fri Sep 15 13:41:28 PDT 2023; root:xnu-8796.141.3.700.8~1/RELEASE_ARM64_T6000 arm64

❯ sw_vers -productVersion          
13.6

❯ quarto check                                                                              
Quarto 1.4.551
[✓] Checking versions of quarto binary dependencies...
      Pandoc version 3.1.11: OK
      Dart Sass version 1.69.5: OK
      Deno version 1.37.2: OK
[✓] Checking versions of quarto dependencies......OK
[✓] Checking Quarto installation......OK
      Version: 1.4.551
      Path: /Applications/quarto/bin

[✓] Checking tools....................OK
      TinyTeX: (not installed)
      Chromium: (not installed)

[✓] Checking LaTeX....................OK
      Using: Installation From Path
      Path: /Library/TeX/texbin
      Version: 2023

[✓] Checking basic markdown render....OK

[✓] Checking Python 3 installation....OK
      Version: 3.10.13
      Path: /xxxx-py3.10/bin/python3
      Jupyter: 5.3.0
      Kernels: ir, julia-1.9, bash, maxima, python3

[✓] Checking Jupyter engine render....OK