10000 gh-93353: Add test.support.late_deletion() by vstinner · Pull Request #93774 · python/cpython · GitHub
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Merged
merged 3 commits into from
Jun 13, 2022
Merged

gh-93353: Add test.support.late_deletion() #93774

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0355bea
gh-93353: Add test.support.late_deletion()
vstinner Jun 13, 2022
84eb078
Rephrase the documentation
vstinner Jun 13, 2022
148bcff
Fix Windows support
vstinner Jun 13, 2022
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35 changes: 35 additions & 0 deletions Lib/test/support/__init__.py
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Original file line number Diff line number Diff line change
Expand Up @@ -2213,3 +2213,38 @@ def requires_venv_with_pip():
# True if Python is built with the Py_DEBUG macro defined: if
# Python is built in debug mode (./configure --with-pydebug).
Py_DEBUG = hasattr(sys, 'gettotalrefcount')


def late_deletion(obj):
"""
Keep a Python alive as long as possible.

Create a reference cycle and store the cycle in an object deleted late in
Python finalization. Try to keep the object alive until the very last
garbage collection.

The function keeps a strong reference by design. It should be called in a
subprocess to not mark a test as "leaking a reference".
"""

# Late CPython finalization:
# - finalize_interp_clear()
# - _PyInterpreterState_Clear()
# - clear os.register_at_fork() callbacks
# - clear codecs.register() callbacks

ref_cycle = [obj]
ref_cycle.append(ref_cycle)

# PyInterpreterState.codec_search_path
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Personally, I would like a bit text here explaining that codec is one of the last modules cleared, but no biggie if you don't care.

Otherwise, LGTM.

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I rephased the doc. Is it better?

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Yes :)

import codecs
def search_func(encoding):
return None
search_func.reference = ref_cycle
codecs.register(search_func)

# PyInterpreterState.before_forkers
def atfork_func():
pass
atfork_func.reference = ref_cycle
os.register_at_fork(before=atfork_func)
14 changes: 4 additions & 10 deletions Lib/test/test_gc.py
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Expand Up @@ -1440,19 +1440,13 @@ def test_ast_fini(self):
code = textwrap.dedent("""
import ast
import codecs
from test import support

# Small AST tree to keep their AST types alive
tree = ast.parse("def f(x, y): return 2*x-y")
x = [tree]
x.append(x)

# Put the cycle somewhere to survive until the last GC collection.
# Codec search functions are only cleared at the end of
# interpreter_clear().
def search_func(encoding):
return None
search_func.a = x
codecs.register(search_func)

# Store the tree somewhere to survive until the last GC collection
support.late_deletion(tree)
""")
assert_python_ok("-c", code)

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