[Bug 6846] New: hg serve with lsprof enabled throws exceptions on cpython 3.12

[mercurial-bugs at mercurial-scm.org]

https://bz.mercurial-scm.org/show_bug.cgi?id=6846

            Bug ID: 6846
           Summary: hg serve with lsprof enabled throws exceptions on
                    cpython 3.12
           Product: Mercurial
           Version: stable branch
          Hardware: PC
                OS: Linux
            Status: UNCONFIRMED
          Severity: bug
          Priority: wish
         Component: hgweb
          Assignee: bugzilla at mercurial-scm.org
          Reporter: coral.pink at disr.it
                CC: mercurial-devel at mercurial-scm.org
    Python Version: ---

Due to changes in python 3.12 in _lsprof module
(https://github.com/python/cpython/issues/103533) multiple profiling contexts
no longer work - at least that's what I think.

The first profiler starts in mercurial.dispatch on start up, and the second one
fails to start in mercurial.hgweb on WSGI request, which crashes request
handling. Removing profiling contexts in mercurial.hgweb makes error go away.

This also causes test-profile.t to fail.

To reproduce:

> hg init
> hg serve --profile --config profiling.type=ls &
listening at http://127.0.0.1:8000/ (bound to *:8000)
> hg clone 'http://127.0.0.1:8000'
127.0.0.1 - - [11/Oct/2023 18:37:08] Exception happened during processing
request '/?cmd=capabilities':
Traceback (most recent call last):
  File "/usr/lib/python3.12/site-packages/mercurial/hgweb/server.py", line 123,
in do_POST
    self.do_write()
  File "/usr/lib/python3.12/site-packages/mercurial/hgweb/server.py", line 117,
in do_write
    self.do_hgweb()
  File "/usr/lib/python3.12/site-packages/mercurial/hgweb/server.py", line 232,
in do_hgweb
    for chunk in self.server.application(env, self._start_response):
  File "/usr/lib/python3.12/site-packages/mercurial/hgweb/hgweb_mod.py", line
364, in run_wsgi
    with profiling.profile(repo.ui, enabled=profile):
  File "/usr/lib/python3.12/site-packages/mercurial/profiling.py", line 197, in
__enter__
    self.start()
  File "/usr/lib/python3.12/site-packages/mercurial/profiling.py", line 262, in
start
    self._profiler.__enter__()
  File "/usr/lib/python3.12/contextlib.py", line 137, in __enter__
    return next(self.gen)
           ^^^^^^^^^^^^^^
  File "/usr/lib/python3.12/site-packages/mercurial/profiling.py", line 58, in
lsprofile
    p.enable(subcalls=True)
ValueError: Another profiling tool is already active

127.0.0.1 - - [11/Oct/2023 18:37:08] "GET /?cmd=capabilities HTTP/1.1" 500 -
abort: HTTP Error 500: Internal Server Error

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