gh-112050: Make collections.deque thread-safe in free-threaded builds

[mpage]

This uses critical sections to make deque methods that operate on mutable state thread-safe when the GIL is disabled. This is mostly accomplished by using the @critical_section clinic directive, though there are a few places where this was not possible and critical sections had to be manually acquired/released.

• Issue: Make collections.deque thread-safe in --disable-gil builds #112050

[erlend-aasland]

I'll get some benchmark numbers in a bit.

Great; let's wait with landing this until we've got those.

[mpage]

@erlend-aasland Here are some benchmark numbers using the default -O3. Let me know if you'd like me to run others. The only substantive change in this PR for default builds is to len, where we're now using an atomic load. I would expect that to be slower, though the benchmark numbers don't appear to confirm that assumption. If we're concerned about a slowdown there we could consider using an ifdef to limit the atomic load to only free-threaded builds.

len

I would expect a slowdown due to the use of atomics, but the data doesn't appear to support that.

This PR:

> ./python -m timeit -s "import collections; d = collections.deque(list(range(100)))" "len(d)" 10000000 loops, best of 5: 21.2 nsec per loop 

main:

> ./python -m timeit -s "import collections; d = collections.deque(list(range(100)))" "len(d)" 10000000 loops, best of 5: 20.8 nsec per loop 

__init__

This should be representative of methods that were annotated with the @critical_section directive. I wouldn't expect any performance change here; the generated acquire/release pair should be a no-op.

This PR:

> ./python -m timeit -s "import collections; L = list(range(100))" "collections.deque(L, 50)" 500000 loops, best of 5: 733 nsec per loop > ./python -m timeit -s "import collections; L = list(range(100))" "collections.deque(L)" 500000 loops, best of 5: 769 nsec per loop 

Main:

> ./python -m timeit -s "import collections; L = list(range(100))" "collections.deque(L, 50)" 500000 loops, best of 5: 731 nsec per loop > ./python -m timeit -s "import collections; L = list(range(100))" "collections.deque(L)" 500000 loops, best of 5: 746 nsec per loop 

contains

This should be representative of methods that had critical sections added manually. In the case of contains, that split the function into two. I wouldn't expect any performance change here in default builds. The compiler should still be able to fully optimize the refactored code.

This PR:

> ./python -m timeit -s "import collections; L = list(range(100))" "50 in L" 500000 loops, best of 5: 512 nsec per loop > ./python -m timeit -s "import collections; L = list(range(100))" "1 in L" 10000000 loops, best of 5: 29.6 nsec per loop > ./python -m timeit -s "import collections; L = list(range(100))" "100 in L" 500000 loops, best of 5: 1.02 usec per loop 

main:

> ./python -m timeit -s "import collections; L = list(range(100))" "50 in L" 500000 loops, best of 5: 520 nsec per loop > ./python -m timeit -s "import collections; L = list(range(100))" "1 in L" 10000000 loops, best of 5: 30.2 nsec per loop > ./python -m timeit -s "import collections; L = list(range(100))" "100 in L" 200000 loops, best of 5: 1 usec per loop > 

[mpage]

@erlend-aasland - I think everything is addressed now. Would you please have another look?

[erlend-aasland]

Thanks!

[erlend-aasland]

I'm inclined to run the buildbots on this; Thomas is cooking up the release right now, so we really don't want one of the bots to turn red right now.

[bedevere-bot]

🤖 New build scheduled with the buildbot fleet by @erlend-aasland for commit 6ffad44 🤖

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

[mpage]

@erlend-aasland - Just noticed one last place where we want to use the macro wrapper. Would you please kick off another buildbot run. Sorry for the churn.

[AlexWaygood]

@erlend-aasland - Just noticed one last place where we want to use the macro wrapper. Would you please kick off another buildbot run. Sorry for the churn.

You should be able to trigger the buildbot run yourself, now you're a triager! :)

[bedevere-bot]

🤖 New build scheduled with the buildbot fleet by @mpage for commit fa7e8a8 🤖

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

[mpage]

You should be able to trigger the buildbot run yourself, now you're a triager! :)

Oho - I'm drunk with power now! :P

[corona10]

LGTM