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gh-146228: Better fork support in cached FastPath#146231

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Merged
jaraco merged 4 commits intopython:mainfromjaraco:gh-146228/forking-fastpath
Mar 20, 2026
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25 changes: 21 additions & 4 deletionsLib/importlib/metadata/__init__.py
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Original file line numberDiff line numberDiff line change
Expand Up@@ -31,7 +31,7 @@

from .import_meta
from ._collectionsimportFreezableDefaultDict,Pair
from ._functoolsimportmethod_cache,pass_none
from ._functoolsimportmethod_cache,noop,pass_none,passthrough
from ._itertoolsimportalways_iterable,bucket,unique_everseen
from ._metaimportPackageMetadata,SimplePath
from ._typingimportmd_none
Expand DownExpand Up@@ -783,6 +783,20 @@ def find_distributions(self, context=Context()) -> Iterable[Distribution]:
"""


@passthrough
def_clear_after_fork(cached):
"""Ensure ``func`` clears cached state after ``fork`` when supported.
``FastPath`` caches zip-backed ``pathlib.Path`` objects that retain a
reference to the parent's open ``ZipFile`` handle. Re-using a cached
instance in a forked child can therefore resurrect invalid file pointers
and trigger ``BadZipFile``/``OSError`` failures (python/importlib_metadata#520).
Registering ``cache_clear`` with ``os.register_at_fork`` keeps each process
on its own cache.
"""
getattr(os,'register_at_fork',noop)(after_in_child=cached.cache_clear)


classFastPath:
"""
Micro-optimized class for searching a root for children.
Expand All@@ -799,7 +813,8 @@ class FastPath:
True
"""

@functools.lru_cache()# type: ignore[misc]
@_clear_after_fork# type: ignore[misc]
@functools.lru_cache()
def__new__(cls,root):
returnsuper().__new__(cls)

Expand DownExpand Up@@ -925,10 +940,12 @@ def __init__(self, name: str | None):
defnormalize(name):
"""
PEP 503 normalization plus dashes as underscores.
Specifically avoids ``re.sub`` as prescribed for performance
benefits (see python/cpython#143658).
"""
# Much faster than re.sub, and even faster than str.translate
value=name.lower().replace("-","_").replace(".","_")
# Condense repeats (faster than regex)
# Condense repeats
while"__"invalue:
value=value.replace("__","_")
returnvalue
Expand Down
3 changes: 2 additions & 1 deletionLib/importlib/metadata/_adapters.py
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Expand Up@@ -9,7 +9,8 @@
classRawPolicy(email.policy.EmailPolicy):
deffold(self,name,value):
folded=self.linesep.join(
textwrap.indent(value,prefix=' '*8,predicate=lambdaline:True)
textwrap
.indent(value,prefix=' '*8,predicate=lambdaline:True)
.lstrip()
.splitlines()
)
Expand Down
32 changes: 32 additions & 0 deletionsLib/importlib/metadata/_functools.py
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Original file line numberDiff line numberDiff line change
@@ -1,5 +1,7 @@
import functools
import types
from collections.abc import Callable
from typing import TypeVar


# from jaraco.functools 3.3
Expand DownExpand Up@@ -102,3 +104,33 @@ def wrapper(param, *args, **kwargs):
return func(param, *args, **kwargs)

return wrapper


# From jaraco.functools 4.4
def noop(*args, **kwargs):
"""
A no-operation function that does nothing.

>>> noop(1, 2, three=3)
"""


_T = TypeVar('_T')


# From jaraco.functools 4.4
def passthrough(func: Callable[..., object]) -> Callable[[_T], _T]:
"""
Wrap the function to always return the first parameter.

>>> passthrough(print)('3')
3
'3'
"""

@functools.wraps(func)
def wrapper(first: _T, *args, **kwargs) -> _T:
func(first, *args, **kwargs)
return first

return wrapper # type: ignore[return-value]
8 changes: 1 addition & 7 deletionsLib/test/test_importlib/metadata/fixtures.py
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Original file line numberDiff line numberDiff line change
Expand Up@@ -6,6 +6,7 @@
importshutil
importsys
importtextwrap
fromimportlibimportresources

fromtest.supportimportimport_helper
fromtest.supportimportos_helper
Expand All@@ -14,11 +15,6 @@
from .import_path
from ._pathimportFilesSpec

ifsys.version_info>= (3,9):
fromimportlibimportresources
else:
importimportlib_resourcesasresources


@contextlib.contextmanager
deftmp_path():
Expand DownExpand Up@@ -374,8 +370,6 @@ def setUp(self):
# Add self.zip_name to the front of sys.path.
self.resources=contextlib.ExitStack()
self.addCleanup(self.resources.close)
# workaround for #138313
self.addCleanup(lambda:None)


defparameterize(*args_set):
Expand Down
58 changes: 28 additions & 30 deletionsLib/test/test_importlib/metadata/test_api.py
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Original file line numberDiff line numberDiff line change
Expand Up@@ -317,33 +317,31 @@ def test_invalidate_cache(self):


classPreparedTests(unittest.TestCase):
deftest_normalize(self):
tests= [
# Simple
("sample","sample"),
# Mixed case
("Sample","sample"),
("SAMPLE","sample"),
("SaMpLe","sample"),
# Separator conversions
("sample-pkg","sample_pkg"),
("sample.pkg","sample_pkg"),
("sample_pkg","sample_pkg"),
# Multiple separators
("sample---pkg","sample_pkg"),
("sample___pkg","sample_pkg"),
("sample...pkg","sample_pkg"),
# Mixed separators
("sample-._pkg","sample_pkg"),
("sample_.-pkg","sample_pkg"),
# Complex
("Sample__Pkg-name.foo","sample_pkg_name_foo"),
("Sample__Pkg.name__foo","sample_pkg_name_foo"),
# Uppercase with separators
("SAMPLE-PKG","sample_pkg"),
("Sample.Pkg","sample_pkg"),
("SAMPLE_PKG","sample_pkg"),
]
forname,expectedintests:
withself.subTest(name=name):
self.assertEqual(Prepared.normalize(name),expected)
@fixtures.parameterize(
# Simple
dict(input='sample',expected='sample'),
# Mixed case
dict(input='Sample',expected='sample'),
dict(input='SAMPLE',expected='sample'),
dict(input='SaMpLe',expected='sample'),
# Separator conversions
dict(input='sample-pkg',expected='sample_pkg'),
dict(input='sample.pkg',expected='sample_pkg'),
dict(input='sample_pkg',expected='sample_pkg'),
# Multiple separators
dict(input='sample---pkg',expected='sample_pkg'),
dict(input='sample___pkg',expected='sample_pkg'),
dict(input='sample...pkg',expected='sample_pkg'),
# Mixed separators
dict(input='sample-._pkg',expected='sample_pkg'),
dict(input='sample_.-pkg',expected='sample_pkg'),
# Complex
dict(input='Sample__Pkg-name.foo',expected='sample_pkg_name_foo'),
dict(input='Sample__Pkg.name__foo',expected='sample_pkg_name_foo'),
# Uppercase with separators
dict(input='SAMPLE-PKG',expected='sample_pkg'),
dict(input='Sample.Pkg',expected='sample_pkg'),
dict(input='SAMPLE_PKG',expected='sample_pkg'),
)
deftest_normalize(self,input,expected):
self.assertEqual(Prepared.normalize(input),expected)
2 changes: 1 addition & 1 deletionLib/test/test_importlib/metadata/test_main.py
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Original file line numberDiff line numberDiff line change
Expand Up@@ -2,12 +2,12 @@
importpickle
importre
importunittest
fromtest.supportimportos_helper

try:
importpyfakefs.fake_filesystem_unittestasffs
exceptImportError:
from .stubsimportfake_filesystem_unittestasffs
fromtest.supportimportos_helper

fromimportlib.metadataimport (
Distribution,
Expand Down
37 changes: 37 additions & 0 deletionsLib/test/test_importlib/metadata/test_zip.py
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Original file line numberDiff line numberDiff line change
@@ -1,7 +1,12 @@
importmultiprocessing
importos
importsys
importunittest

fromtest.supportimportwarnings_helper

fromimportlib.metadataimport (
FastPath,
PackageNotFoundError,
distribution,
distributions,
Expand DownExpand Up@@ -47,6 +52,38 @@ def test_one_distribution(self):
dists=list(distributions(path=sys.path[:1]))
assertlen(dists)==1

@warnings_helper.ignore_fork_in_thread_deprecation_warnings()
@unittest.skipUnless(
hasattr(os,'register_at_fork')
and'fork'inmultiprocessing.get_all_start_methods(),
'requires fork-based multiprocessing support',
)
deftest_fastpath_cache_cleared_in_forked_child(self):
zip_path=sys.path[0]

FastPath(zip_path)
assertFastPath.__new__.cache_info().currsize>=1

ctx=multiprocessing.get_context('fork')
parent_conn,child_conn=ctx.Pipe()

defchild(conn,root):
try:
before=FastPath.__new__.cache_info().currsize
FastPath(root)
after=FastPath.__new__.cache_info().currsize
conn.send((before,after))
finally:
conn.close()

proc=ctx.Process(target=child,args=(child_conn,zip_path))
proc.start()
child_conn.close()
cache_sizes=parent_conn.recv()
proc.join()

self.assertEqual(cache_sizes, (0,1))


classTestEgg(TestZip):
defsetUp(self):
Expand Down
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Original file line numberDiff line numberDiff line change
@@ -0,0 +1,2 @@
Cached FastPath objects in importlib.metadata are now cleared on fork,
avoiding broken references to zip files during fork.
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