gh-112087: Update list impl to be thread-safe with manual CS

[corona10]

• Issue: Make list objects thread-safe in --disable-gil builds #112087

[corona10]

The rest of the parts can be separated into two parts.
A. xxx_lock implementations.
B. Where PyList_FetchItem is needed.

A is a headache; atomic operation with default build will require some overhead than pure operation; not sure how we can solve this with a seamless approach.

B is quite simple; if we already have similar APIs, then we can just use them. If not, we should introduce one.

[colesbury]

Looks good other than the unused variable.

I scanned through listobject.c and it looks like there are still other functions that should be fairly straightforward to make thread-safe, such as list_copy_impl and list_append.

What do you mean by "xxx_lock implementations"?

[corona10]

@colesbury Updated PTAL :)

[corona10]

What do you mean by "xxx_lock implementations"?

It was about list_item_locked things that you updated implementations to use _Py_atomic_store/load operations.

[colesbury]

LGTM.

I wonder if it's worth doing something to abstract out the locking in type slots (like tp_richcompare).

[corona10]

I wonder if it's worth doing something to abstract out the locking in type slots (like tp_richcompare).

It might be up to case, list_richcompare was too complex case to handle without extracting core logics.