gh-112075: Fix dict thread safety issues

[Kronuz]

Summary:

For dicts, there are a myriad of variables that are atomics. i.e.:

mp->ma_used
mp->ma_keys
mp->ma_values
entry_ptr->me_value
entry_ptr->me_key
entry_ptr->me_hash
di->di_pos
di->len
values->values[ix]
values->capacity
values->size
keys->dk_nentries
keys->dk_usable
op->ob_ref_shared

All of these can be accessed in write or read mode. When these are being accessed in write mode, regardless of the status of the dictionary lock, the write should be an atomic store. All reads must be atomic loads if the lock is not held, or can be non-atomic reads otherwise.

This diff goes through all of the ma_used use cases and makes sure this holds true.

---

Test Plan:

./configure --disable-gil --with-thread-sanitizer --with-pydebug
make -j
env TSAN_OPTIONS=suppressions=Tools/tsan/suppressions_free_threading.txt ./python -m test --tsan -j4

All tests passing, no related TSAN issues.

---

• Issue: Make dict objects thread-safe in --disable-gil builds #112075

[DinoV]

LGTM!

[colesbury]

I think we should backport this to 3.13

[miss-islington-app]

Thanks @Kronuz for the PR, and @DinoV for merging it 🌮🎉.. I'm working now to backport this PR to: 3.13.
🐍🍒⛏🤖

[bedevere-app]

GH-121545 is a backport of this pull request to the 3.13 branch.

[bedevere-bot]

⚠️⚠️⚠️ Buildbot failure ⚠️⚠️⚠️

Hi! The buildbot AMD64 Windows11 Bigmem 3.13 has failed when building commit 2f15383.

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/all/#builders/1463/builds/226) and take a look at the build logs.
4. Check if the failure is related to this commit (2f15383) 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/all/#builders/1463/builds/226

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

Click to see traceback logs

remote: Enumerating objects: 4, done.        
remote: Counting objects:  25% (1/4)        
remote: Counting objects:  50% (2/4)        
remote: Counting objects:  75% (3/4)        
remote: Counting objects: 100% (4/4)        
remote: Counting objects: 100% (4/4), done.        
remote: Total 4 (delta 3), reused 3 (delta 3), pack-reused 0        
From https://github.com/python/cpython
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HEAD is now at 2f15383161 [3.13] gh-112075: Fix dict thread safety issues (GH-119288) (#121545)
Switched to and reset branch '3.13'