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[3.11] gh-117178: Recover lazy loading of self-referential modules (GH-117179) (#117320)

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Co-authored-by: Chris Markiewicz <effigies@gmail.com>
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Miss Islington (bot) 2024-03-28 12:17:10 +01:00 • committed by GitHub
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3 changed files with 25 additions and 6 deletions
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11
Lib/importlib/util.py
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@ -232,12 +232,11 @@ class _LazyModule(types.ModuleType):
# Only the first thread to get the lock should trigger the load
# and reset the module's class. The rest can now getattr().
if object.__getattribute__(self, '__class__') is _LazyModule:
# The first thread comes here multiple times as it descends the
# call stack. The first time, it sets is_loading and triggers
# exec_module(), which will access module.__dict__, module.__name__,
# and/or module.__spec__, reentering this method. These accesses
# need to be allowed to proceed without triggering the load again.
if loader_state['is_loading'] and attr.startswith('__') and attr.endswith('__'):
# Reentrant calls from the same thread must be allowed to proceed without
# triggering the load again.
# exec_module() and self-referential imports are the primary ways this can
# happen, but in any case we must return something to avoid deadlock.
if loader_state['is_loading']:
return object.__getattribute__(self, attr)
loader_state['is_loading'] = True