gh-92810: Reduce memory usage by ABCMeta.__subclasscheck__ (alternative)

[dolfinus]

• Issue: _abc._abc_subclasscheck has very poor performance and (I think) a memory leak #92810

Alternative implementation of #131914 which doesn't modify class attributes on every __subclasscheck__ call. Instead it checks in __new__ does current class have def __subclasses__(cls) overriden, and if so, enables case for scls in cls.__subclasses__(), which is disabled by default.
To handle cases like:

class Number(ABC): ...

class Real(Number): ...

class Integral(Real): ...

Integral.register(int)

assert issubclass(int, Number) is True

which previously were implemented via __subclasses__, method cls.register(subclass) is calling super(cls).register(subclass) recursively ("bubble-up" registration to all the parents).

For benchmark from #131914:

sudo ./python -m pyperf system tune
taskset -c 0 ./python benchmark.py --metaclass abc.ABCMeta --rounds 3 --classes 5000
taskset -c 0 ./python benchmark.py --metaclass _py_abc.ABCMeta --rounds 3 --classes 5000

Impl	Max memory before, MB	Max memory after, MB
_abc	6332	47
_py_abc	4423	58

Impl	Total time before	Total time after
_abc	19m 57s	2m 6s
_py_abc	17m 14s	6m 14s

Check	Impl	before	after	Impl	before	after
isinstance(child, Parent)	_abc	0.194us 2MiB...15MiB	0.190us 2MiB...15MiB	_py_abc	0.337us 10MiB...24MiB	0.345us 10MiB...24MiB
issubclass(Child, Parent)	_abc	0.179us 0MiB...1MiB	0.177us 0MiB...1MiB	_py_abc	0.326us 6MiB...8MiB	0.331us 5MiB...8MiB
isinstance(child, Grandparent)	_abc	0.188us 0MiB...2MiB	0.185us 0MiB...1MiB	_py_abc	0.331us 4MiB...7MiB	0.337us 4MiB...7MiB
issubclass(Child, Grandparent)	_abc	0.173us 0MiB	0.173us 0MiB	_py_abc	0.324us 1MiB...2MiB	0.327us 0MiB...1MiB
not isinstance(child, Sibling)	_abc	0.189us 1MiB...14MiB	0.184us 1MiB...14MiB	_py_abc	0.567us 14MiB...24MiB	0.566us 13MiB...22MiB
not issubclass(Child, Sibling)	_abc	0.172us 0MiB	0.176us 0MiB...1MiB	_py_abc	0.526us 9MiB...11MiB	0.520us 8MiB...11MiB
not isinstance(child, Cousin)	_abc	0.189us 0MiB	0.184us 1MiB...2MiB	_py_abc	0.558us 8MiB...10MiB	0.565us 6MiB...8MiB
not issubclass(Child, Cousin)	_abc	0.172us 0MiB	0.175us 0MiB...1MiB	_py_abc	0.522us 5MiB...6MiB	0.522us 2MiB...3MiB
not isinstance(child, Uncle)	_abc	8.126us 5706MiB...6331MiB	0.191us 0MiB...1MiB	_py_abc	13.092us 3796MiB...4423MiB	0.571us 5MiB
not issubclass(Child, Uncle)	_abc	8.029us 5704MiB	0.180us 0MiB	_py_abc	13.174us 3794MiB...3795MiB	0.526us 3MiB

Memory increment is measured during isinstance() / issubclass() calls, not during preparation, like class creation or registration where actual registry allocation is performed. So memory usage in tables below is almost always 0.

Timing drop in _py_abc implementation for 2 first rows is due to if subclass in cls._abc_registry: check added to match _abc.c implementation.

Check	Impl	before	after	Impl	before	after
isinstance(child, Parent.register)	_abc	0.413us 0MiB	0.401us 0MiB	_py_abc	0.689us 0MiB	0.439us 0MiB
issubclass(Child, Parent.register)	_abc	0.249us 0MiB	0.246us 0MiB	_py_abc	0.671us 0MiB	0.422us 0MiB
isinstance(child, Grandparent.register)	_abc	0.188us 0MiB	0.184us 0MiB	_py_abc	0.399us 0MiB	0.413us 0MiB
issubclass(Child, Grandparent.register)	_abc	0.174us 0MiB	0.175us 0MiB	_py_abc	0.386us 0MiB	0.396us 0MiB
not isinstance(child, Sibling.register)	_abc	0.042us 0MiB	0.042us 1MiB	_py_abc	0.042us 0MiB	0.042us 2MiB
not issubclass(Child, Sibling.register)	_abc	0.028us 0MiB	0.028us 1MiB	_py_abc	0.028us 0MiB	0.027us 2MiB
not isinstance(child, Cousin.register)	_abc	0.042us 0MiB	0.042us 2MiB	_py_abc	0.042us 0MiB	0.041us 3MiB
not issubclass(Child, Cousin.register)	_abc	0.028us 0MiB	0.028us 2MiB	_py_abc	0.028us 0MiB	0.032us 3MiB
not isinstance(child, Uncle.register)	_abc	0.372us 0MiB	0.365us 2MiB...3MiB	_py_abc	1.350us 0MiB	1.398us 4MiB
not issubclass(Child, Uncle.register)	_abc	0.359us 0MiB	0.354us 2MiB	_py_abc	1.321us 0MiB	1.362us 4MiB

Check	Impl	before	after	Impl	before	after
isinstance(child, Parent.__subclasses__)	_abc	0.211us 0MiB	0.206us 0MiB	_py_abc	0.472us 0MiB	0.485us 0MiB
issubclass(Child, Parent.__subclasses__)	_abc	0.197us 0MiB	0.193us 0MiB	_py_abc	0.458us 0MiB	0.469us 0MiB
isinstance(child, Grandparent.__subclasses__)	_abc	0.205us 0MiB	0.201us 0MiB	_py_abc	0.470us 0MiB	0.483us 0MiB
issubclass(Child, Grandparent.__subclasses__)	_abc	0.190us 0MiB	0.191us 0MiB	_py_abc	0.458us 0MiB	0.470us 0MiB
not isinstance(child, Sibling.__subclasses__)	_abc	0.042us 0MiB	0.042us 0MiB	_py_abc	0.042us 0MiB	0.042us 1MiB
not issubclass(Child, Sibling.__subclasses__)	_abc	0.028us 0MiB	0.027us 0MiB	_py_abc	0.028us 0MiB	0.028us 1MiB
not isinstance(child, Cousin.__subclasses__)	_abc	0.042us 0MiB	0.042us 0MiB	_py_abc	0.042us 0MiB	0.041us 1MiB
not issubclass(Child, Cousin.__subclasses__)	_abc	0.028us 0MiB	0.027us 0MiB	_py_abc	0.028us 0MiB	0.027us 1MiB
not isinstance(child, Uncle.__subclasses__)	_abc	0.237us 0MiB	0.237us 1MiB	_py_abc	0.877us 0MiB	0.925us 2MiB
not issubclass(Child, Uncle.__subclasses__)	_abc	0.223us 0MiB	0.226us 1MiB	_py_abc	0.839us 0MiB	0.865us 2MiB

Flamegraphs for _py_abc impl and test issubclass_uncle (the most time and memory consuming case on main):
main_vs_pr141171.tar.gz

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[dolfinus]

pyperformance results doesn't show a much difference:

sudo ./venv/bin/python -m pyperf system tune
./venv/bin/python -m pyperformance run --rigorous --affinity 0,1,2,3,4,5

main_cd4d0ae75c_rigorous_affinity.json
pr141171_rigorous_affinity.json

Details

Benchmarks with tag 'apps':

Benchmark	main_cd4d0ae75c_rigorous_affinity	pr141171_rigorous_affinity
chameleon	18.4 ms	18.6 ms: 1.01x slower
sphinx	1.13 sec	1.14 sec: 1.00x slower
Geometric mean	(ref)	1.00x slower

Benchmark hidden because not significant (4): 2to3, docutils, html5lib, tornado_http

Benchmarks with tag 'asyncio':

Benchmark	main_cd4d0ae75c_rigorous_affinity	pr141171_rigorous_affinity
async_tree_eager_memoization	225 ms	216 ms: 1.04x faster
async_tree_eager_io_tg	627 ms	617 ms: 1.02x faster
async_tree_eager_tg	263 ms	259 ms: 1.02x faster
asyncio_tcp	376 ms	378 ms: 1.01x slower
async_tree_cpu_io_mixed	667 ms	673 ms: 1.01x slower
async_tree_eager_cpu_io_mixed	536 ms	540 ms: 1.01x slower
async_tree_eager_cpu_io_mixed_tg	615 ms	626 ms: 1.02x slower
async_generators	501 ms	512 ms: 1.02x slower
coroutines	26.7 ms	27.9 ms: 1.05x slower
async_tree_eager_io	629 ms	659 ms: 1.05x slower
Geometric mean	(ref)	1.01x slower

Benchmark hidden because not significant (11): async_tree_none_tg, async_tree_eager, async_tree_memoization, async_tree_eager_memoization_tg, asyncio_websockets, async_tree_io_tg, asyncio_tcp_ssl, async_tree_memoization_tg, async_tree_io, async_tree_none, async_tree_cpu_io_mixed_tg

Benchmarks with tag 'math':

Benchmark	main_cd4d0ae75c_rigorous_affinity	pr141171_rigorous_affinity
nbody	109 ms	106 ms: 1.03x faster
pidigits	287 ms	288 ms: 1.00x slower
Geometric mean	(ref)	1.01x faster

Benchmark hidden because not significant (1): float

Benchmarks with tag 'regex':

Benchmark	main_cd4d0ae75c_rigorous_affinity	pr141171_rigorous_affinity
regex_v8	23.9 ms	22.4 ms: 1.07x faster
regex_effbot	2.88 ms	2.81 ms: 1.02x faster
regex_dna	199 ms	194 ms: 1.02x faster
Geometric mean	(ref)	1.03x faster

Benchmark hidden because not significant (1): regex_compile

Benchmarks with tag 'serialize':

Benchmark	main_cd4d0ae75c_rigorous_affinity	pr141171_rigorous_affinity
unpickle_list	5.37 us	5.20 us: 1.03x faster
pickle_list	5.04 us	4.95 us: 1.02x faster
xml_etree_process	77.6 ms	76.4 ms: 1.02x faster
xml_etree_iterparse	106 ms	105 ms: 1.01x faster
unpickle_pure_python	254 us	252 us: 1.01x faster
xml_etree_generate	111 ms	110 ms: 1.01x faster
xml_etree_parse	166 ms	167 ms: 1.00x slower
json_dumps	10.9 ms	11.0 ms: 1.01x slower
tomli_loads	2.25 sec	2.28 sec: 1.01x slower
json_loads	27.4 us	28.1 us: 1.02x slower
Geometric mean	(ref)	1.00x faster

Benchmark hidden because not significant (4): pickle_pure_python, pickle_dict, pickle, unpickle

Benchmarks with tag 'startup':

Benchmark	main_cd4d0ae75c_rigorous_affinity	pr141171_rigorous_affinity
python_startup_no_site	7.99 ms	8.04 ms: 1.01x slower
python_startup	13.8 ms	14.0 ms: 1.01x slower
Geometric mean	(ref)	1.01x slower

Benchmarks with tag 'template':

Benchmark	main_cd4d0ae75c_rigorous_affinity	pr141171_rigorous_affinity
genshi_xml	59.0 ms	58.4 ms: 1.01x faster
mako	12.6 ms	12.7 ms: 1.01x slower
genshi_text	25.6 ms	25.9 ms: 1.01x slower
Geometric mean	(ref)	1.00x slower

All benchmarks:

Benchmark	main_cd4d0ae75c_rigorous_affinity	pr141171_rigorous_affinity
regex_v8	23.9 ms	22.4 ms: 1.07x faster
async_tree_eager_memoization	225 ms	216 ms: 1.04x faster
unpickle_list	5.37 us	5.20 us: 1.03x faster
unpack_sequence	47.9 ns	46.5 ns: 1.03x faster
fannkuch	460 ms	447 ms: 1.03x faster
nbody	109 ms	106 ms: 1.03x faster
nqueens	103 ms	100 ms: 1.02x faster
regex_effbot	2.88 ms	2.81 ms: 1.02x faster
regex_dna	199 ms	194 ms: 1.02x faster
hexiom	6.63 ms	6.49 ms: 1.02x faster
pickle_list	5.04 us	4.95 us: 1.02x faster
deepcopy_memo	29.3 us	28.8 us: 1.02x faster
async_tree_eager_io_tg	627 ms	617 ms: 1.02x faster
xml_etree_process	77.6 ms	76.4 ms: 1.02x faster
async_tree_eager_tg	263 ms	259 ms: 1.02x faster
deepcopy	296 us	292 us: 1.02x faster
typing_runtime_protocols	198 us	196 us: 1.01x faster
logging_format	7.41 us	7.34 us: 1.01x faster
genshi_xml	59.0 ms	58.4 ms: 1.01x faster
scimark_lu	129 ms	128 ms: 1.01x faster
xml_etree_iterparse	106 ms	105 ms: 1.01x faster
unpickle_pure_python	254 us	252 us: 1.01x faster
dulwich_log	72.3 ms	71.7 ms: 1.01x faster
xml_etree_generate	111 ms	110 ms: 1.01x faster
xdsl_constant_fold	52.4 ms	52.0 ms: 1.01x faster
deepcopy_reduce	3.36 us	3.34 us: 1.01x faster
bpe_tokeniser	5.31 sec	5.29 sec: 1.00x faster
mdp	1.48 sec	1.48 sec: 1.00x slower
pidigits	287 ms	288 ms: 1.00x slower
sphinx	1.13 sec	1.14 sec: 1.00x slower
sqlalchemy_declarative	143 ms	144 ms: 1.00x slower
xml_etree_parse	166 ms	167 ms: 1.00x slower
gc_traversal	4.99 ms	5.02 ms: 1.01x slower
python_startup_no_site	7.99 ms	8.04 ms: 1.01x slower
create_gc_cycles	2.40 ms	2.42 ms: 1.01x slower
asyncio_tcp	376 ms	378 ms: 1.01x slower
bench_thread_pool	1.06 ms	1.07 ms: 1.01x slower
sqlglot_v2_parse	1.41 ms	1.42 ms: 1.01x slower
mako	12.6 ms	12.7 ms: 1.01x slower
async_tree_cpu_io_mixed	667 ms	673 ms: 1.01x slower
async_tree_eager_cpu_io_mixed	536 ms	540 ms: 1.01x slower
subparsers	46.5 ms	46.9 ms: 1.01x slower
coverage	125 ms	127 ms: 1.01x slower
chameleon	18.4 ms	18.6 ms: 1.01x slower
comprehensions	18.6 us	18.8 us: 1.01x slower
python_startup	13.8 ms	14.0 ms: 1.01x slower
json_dumps	10.9 ms	11.0 ms: 1.01x slower
genshi_text	25.6 ms	25.9 ms: 1.01x slower
tomli_loads	2.25 sec	2.28 sec: 1.01x slower
logging_simple	6.51 us	6.58 us: 1.01x slower
deltablue	3.54 ms	3.59 ms: 1.01x slower
chaos	66.1 ms	67.0 ms: 1.01x slower
raytrace	325 ms	330 ms: 1.01x slower
scimark_fft	309 ms	313 ms: 1.02x slower
richards_super	57.5 ms	58.5 ms: 1.02x slower
telco	8.59 ms	8.74 ms: 1.02x slower
scimark_monte_carlo	73.9 ms	75.2 ms: 1.02x slower
generators	34.3 ms	34.9 ms: 1.02x slower
async_tree_eager_cpu_io_mixed_tg	615 ms	626 ms: 1.02x slower
crypto_pyaes	80.9 ms	82.4 ms: 1.02x slower
async_generators	501 ms	512 ms: 1.02x slower
json_loads	27.4 us	28.1 us: 1.02x slower
pathlib	15.2 ms	15.6 ms: 1.02x slower
richards	49.4 ms	51.1 ms: 1.03x slower
logging_silent	114 ns	118 ns: 1.04x slower
spectral_norm	106 ms	110 ms: 1.04x slower
coroutines	26.7 ms	27.9 ms: 1.05x slower
async_tree_eager_io	629 ms	659 ms: 1.05x slower
Geometric mean	(ref)	1.00x slower

Benchmark hidden because not significant (36): bench_mp_pool, html5lib, meteor_contest, scimark_sor, docutils, pprint_pformat, regex_compile, pickle_pure_python, async_tree_none_tg, pickle_dict, async_tree_eager, tornado_http, dask, pyflate, go, scimark_sparse_mat_mult, async_tree_memoization, pickle, async_tree_eager_memoization_tg, asyncio_websockets, many_optionals, sqlglot_v2_normalize, pprint_safe_repr, 2to3, float, unpickle, async_tree_io_tg, asyncio_tcp_ssl, async_tree_memoization_tg, async_tree_io, sqlite_synth, sqlalchemy_imperative, sqlglot_v2_optimize, sqlglot_v2_transpile, async_tree_none, async_tree_cpu_io_mixed_tg

[dolfinus]

If for scls in cls.__subclasses__() was added only to handle nested ABC classes registration, like this:

class Number(ABC): ...

class Real(Number): ...

Real.register(int)
Real.register(float)

assert issubclass(int, Number)
assert issubclass(float, Number)

then it is not required anymore. In this case _abc_should_check_subclasses check and new tests with __subclasses__ overrides can be dropped.

I haven't found any uses of the such overrides with ABC/ABCMeta, other than implementing custom non-ABC metaclasses or using this as typeshed annotations in .pyi files:
https://github.com/search?q=%22def+__subclasses__%22+language%3APython&type=code&ref=advsearch&p=1
https://github.com/search?q=%22__subclasses__+%3D%22+language%3APython&type=code&ref=advsearch&p=1