GeezerVison

@colesbury

• listiter_reduce_general looks safe, so I think that we don't have to touch it.
• The rest of the APIs can be migrated once the gh-114329: Add PyList_GetItemRef function #114504 is merged.

Regarding iterators: list (and dict) iterators current clear it->it_seq field when the iterator is exhausted. This will make it harder to make the iterators thread-safe because it_seq is mutable. In the free-threaded build, I think we should avoid clearing the it_seq field until the iterator is deallocated.

@colesbury
I will update the implementation through this PR after #114916 is merged :)

@colesbury
#114843 (review)
I addressed your code review, including the change of implementation details when the iterator is exhausted.

Since it touched on the implementation details, I think that we should listen to other core developers' opinions, too.

1. Change it from CPython 3.13 for the default build and free-threaded build
2. Only change it for a free-threaded build (Be more complex but possible option)

cc @carljm @JelleZijlstra

@gvanrossum
I only touched the tier 1 opcode, but if we need to touch the tier 2 opcode too, please let me know.
The refleak test for tier 2 of test_list and test_iter had already failed in the main branch.

Tier 1

$> ./python.exe -m test test_list test_iter -R 3:3
Using random seed: 1891590703
Raised RLIMIT_NOFILE: 256 -> 1024
0:00:00 load avg: 5.97 Run 2 tests sequentially
0:00:00 load avg: 5.97 [1/2] test_list
beginning 6 repetitions
123456
......
0:00:01 load avg: 5.73 [2/2] test_iter
beginning 6 repetitions
123456
......

== Tests result: SUCCESS ==

All 2 tests OK.

Total duration: 1.9 sec
Total tests: run=114
Total test files: run=2/2
Result: SUCCESS

Tier 2

$ ./python.exe -Xuops -m test test_list test_iter -R 3:3
Using random seed: 542131965
Raised RLIMIT_NOFILE: 256 -> 1024
0:00:00 load avg: 6.22 Run 2 tests sequentially
0:00:00 load avg: 6.22 [1/2] test_list
beginning 6 repetitions
123456
......
test_list leaked [4, 3, 2] references, sum=9
test_list leaked [6, 4, 4] memory blocks, sum=14
0:00:01 load avg: 6.22 [2/2/1] test_iter -- test_list failed (reference leak)
beginning 6 repetitions
123456
......
test_iter leaked [8, 9, 6] references, sum=23
test_iter leaked [12, 11, 8] memory blocks, sum=31
test_iter failed (reference leak)

== Tests result: FAILURE ==

2 tests failed:
    test_iter test_list

Total duration: 2.0 sec
Total tests: run=114
Total test files

@gvanrossum @colesbury gentle ping :)

@gvanrossum @colesbury gentle ping :)

I trust Sam. My queue is very long and my proessing capacity is reduced.