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gh-130094: Fix race conditions in importlib (gh-130101)

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Entries may be added or removed from `sys.meta_path` concurrently. For
example, setuptools temporarily adds and removes the `distutils` finder from
the beginning of the list. The local copy ensures that we don't skip over any
entries.

Some packages modify `sys.modules` during import. For example, `collections`
inserts the entry for `collections.abc`  into `sys.modules` during import. We
need to ensure that we re-check `sys.modules` *after* the parent module is
fully initialized.
This commit is contained in:
Sam Gross 2025-02-18 18:02:42 -05:00 • committed by GitHub
parent 8207454bc0
commit 857bdba0ac
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2 changed files with 14 additions and 3 deletions
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15
Lib/importlib/_bootstrap.py
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@ -1244,6 +1244,9 @@ def _find_spec(name, path, target=None):
raise ImportError("sys.meta_path is None, Python is likely "
"shutting down")
# gh-130094: Copy sys.meta_path so that we have a consistent view of the
# list while iterating over it.
meta_path = list(meta_path)
if not meta_path:
_warnings.warn('sys.meta_path is empty', ImportWarning)
@ -1298,7 +1301,6 @@ def _sanity_check(name, package, level):
_ERR_MSG_PREFIX = 'No module named '
_ERR_MSG = _ERR_MSG_PREFIX + '{!r}'
def _find_and_load_unlocked(name, import_):
path = None
@ -1308,8 +1310,9 @@ def _find_and_load_unlocked(name, import_):
if parent not in sys.modules:
_call_with_frames_removed(import_, parent)
# Crazy side-effects!
if name in sys.modules:
return sys.modules[name]
module = sys.modules.get(name)
if module is not None:
return module
parent_module = sys.modules[parent]
try:
path = parent_module.__path__
@ -1317,6 +1320,12 @@ def _find_and_load_unlocked(name, import_):
msg = f'{_ERR_MSG_PREFIX}{name!r}; {parent!r} is not a package'
raise ModuleNotFoundError(msg, name=name) from None
parent_spec = parent_module.__spec__
if getattr(parent_spec, '_initializing', False):
_call_with_frames_removed(import_, parent)
# Crazy side-effects (again)!
module = sys.modules.get(name)
if module is not None:
return module
child = name.rpartition('.')[2]
spec = _find_spec(name, path)
if spec is None: