gh-116738: Make mmap module thread-safe

[yoney]

These changes make the mmap module thread-safe for FT-Python by protecting the mmap_object against race conditions and undefined behavior. The goal is to provide behavior similar to standard Python builds with the GIL enabled, rather than making mmap fully deterministic or generally recommended for multithreaded use.

cc: @mpage @colesbury @Yhg1s

• Issue: Audit all built-in modules for thread safety #116738

[ZeroIntensity]

I think that it would be helpful in the long run to switch mmap to AC rather than manually adding lock_held functions everywhere.

[corona10]

Same question from my side:
Why don t we switch to use AC with '@critical_section'?

[yoney]

Same question from my side: Why don t we switch to use AC with '@critical_section'?

@ZeroIntensity, @corona10: Thank you both for the reviews, I agree that using AC with @critical_section would be a better.

I wanted to ask for your preference: would you like to implement the switch in this PR, or should I hold off on this one and do the implementation separately, then continue with this PR after that? Alternatively, the switch could be done as a follow-up PR.

Thanks!

[ZeroIntensity]

Let's do AC in this PR.

[vstinner]

LGTM. I reviewed mmapmodule.c, but I didn't review Lib/test/test_free_threading/test_mmap.py.

[bedevere-bot]

🤖 New build scheduled with the buildbot fleet by @kumaraditya303 for commit 9d6b95d 🤖

Results will be shown at:

https://buildbot.python.org/all/#/grid?branch=refs%2Fpull%2F139237%2Fmerge

If you want to schedule another build, you need to add the 🔨 test-with-buildbots label again.

[miss-islington-app]

Thanks @yoney for the PR, and @kumaraditya303 for merging it 🌮🎉.. I'm working now to backport this PR to: 3.14.
🐍🍒⛏🤖

[miss-islington-app]

Sorry, @yoney and @kumaraditya303, I could not cleanly backport this to 3.14 due to a conflict.
Please backport using cherry_picker on command line.

cherry_picker 7f155f9c46e2dd7dec5e12ebec3323dfd95fe1f0 3.14

[bedevere-app]

GH-139825 is a backport of this pull request to the 3.14 branch.

[bedevere-bot]

⚠️⚠️⚠️ Buildbot failure ⚠️⚠️⚠️

Hi! The buildbot AMD64 FreeBSD Refleaks 3.x (tier-3) has failed when building commit 7f155f9.

What do you need to do:

1. Don't panic.
2. Check the buildbot page in the devguide if you don't know what the buildbots are or how they work.
3. Go to the page of the buildbot that failed (https://buildbot.python.org/#/builders/1613/builds/2130) and take a look at the build logs.
4. Check if the failure is related to this commit (7f155f9) or if it is a false positive.
5. If the failure is related to this commit, please, reflect that on the issue and make a new Pull Request with a fix.

You can take a look at the buildbot page here:

https://buildbot.python.org/#/builders/1613/builds/2130

Test leaking resources:

• test_events: references
• test_events: memory blocks

Summary of the results of the build (if available):

==

Click to see traceback logs

Traceback (most recent call last):
  File "/buildbot/buildarea/3.x.ware-freebsd.refleak/build/Lib/test/support/__init__.py", line 847, in gc_collect
    gc.collect()
    ~~~~~~~~~~^^
ResourceWarning: unclosed <socket.socket fd=9, family=2, type=1, proto=6, laddr=('127.0.0.1', 38818), raddr=('127.0.0.1', 38819)>
Task was destroyed but it is pending!
task: <Task pending name='Task-3140' coro=<BaseSelectorEventLoop._accept_connection2() done, defined at /buildbot/buildarea/3.x.ware-freebsd.refleak/build/Lib/asyncio/selector_events.py:217> wait_for=<Future pending cb=[Task.task_wakeup()]>>
Warning -- Unraisable exception
Exception ignored while calling deallocator <function _SelectorTransport.__del__ at 0x837dda750>:
Traceback (most recent call last):
  File "/buildbot/buildarea/3.x.ware-freebsd.refleak/build/Lib/asyncio/selector_events.py", line 873, in __del__
    _warn(f"unclosed transport {self!r}", ResourceWarning, source=self)
    ~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
ResourceWarning: unclosed transport <_SelectorSocketTransport closing fd=9>
k


Traceback (most recent call last):
  File "/buildbot/buildarea/3.x.ware-freebsd.refleak/build/Lib/test/support/__init__.py", line 847, in gc_collect
    gc.collect()
    ~~~~~~~~~~^^
ResourceWarning: unclosed <socket.socket fd=9, family=2, type=1, proto=6, laddr=('127.0.0.1', 55024), raddr=('127.0.0.1', 55025)>
Task was destroyed but it is pending!
task: <Task pending name='Task-1740' coro=<BaseSelectorEventLoop._accept_connection2() done, defined at /buildbot/buildarea/3.x.ware-freebsd.refleak/build/Lib/asyncio/selector_events.py:217> wait_for=<Future pending cb=[Task.task_wakeup()]>>
Warning -- Unraisable exception
Exception ignored while calling deallocator <function _SelectorTransport.__del__ at 0x841981250>:
Traceback (most recent call last):
  File "/buildbot/buildarea/3.x.ware-freebsd.refleak/build/Lib/asyncio/selector_events.py", line 873, in __del__
    _warn(f"unclosed transport {self!r}", ResourceWarning, source=self)
    ~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
ResourceWarning: unclosed transport <_SelectorSocketTransport closing fd=9>
k