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gh-92452: Avoid race in initialization of sysconfig._CONFIG_VARS #92453

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Merged
merged 2 commits into from
Oct 28, 2022
Merged

gh-92452: Avoid race in initialization of sysconfig._CONFIG_VARS #92453

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17556a5
Avoid race in initialization of sysconfig._CONFIG_VARS (GH-92452)
gareth-rees May 8, 2022
7c914bb
move init_config_vars outside get_config_vars
FFY00 Oct 28, 2022
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140 changes: 80 additions & 60 deletions Lib/sysconfig.py
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Original file line number Diff line number Diff line change
Expand Up @@ -2,6 +2,7 @@

import os
import sys
import threading
from os.path import pardir, realpath

__all__ = [
Expand Down Expand Up @@ -172,7 +173,11 @@ def joinuser(*args):
_BASE_PREFIX = os.path.normpath(sys.base_prefix)
_EXEC_PREFIX = os.path.normpath(sys.exec_prefix)
_BASE_EXEC_PREFIX = os.path.normpath(sys.base_exec_prefix)
# Mutex guarding initialization of _CONFIG_VARS.
_CONFIG_VARS_LOCK = threading.RLock()
_CONFIG_VARS = None
# True iff _CONFIG_VARS has been fully initialized.
_CONFIG_VARS_INITIALIZED = False
_USER_BASE = None

# Regexes needed for parsing Makefile (and similar syntaxes,
Expand Down Expand Up @@ -625,6 +630,71 @@ def get_path(name, scheme=get_default_scheme(), vars=None, expand=True):
return get_paths(scheme, vars, expand)[name]


def _init_config_vars():
global _CONFIG_VARS
_CONFIG_VARS = {}
# Normalized versions of prefix and exec_prefix are handy to have;
# in fact, these are the standard versions used most places in the
# Distutils.
_CONFIG_VARS['prefix'] = _PREFIX
_CONFIG_VARS['exec_prefix'] = _EXEC_PREFIX
_CONFIG_VARS['py_version'] = _PY_VERSION
_CONFIG_VARS['py_version_short'] = _PY_VERSION_SHORT
_CONFIG_VARS['py_version_nodot'] = _PY_VERSION_SHORT_NO_DOT
_CONFIG_VARS['installed_base'] = _BASE_PREFIX
_CONFIG_VARS['base'] = _PREFIX
_CONFIG_VARS['installed_platbase'] = _BASE_EXEC_PREFIX
_CONFIG_VARS['platbase'] = _EXEC_PREFIX
_CONFIG_VARS['projectbase'] = _PROJECT_BASE
_CONFIG_VARS['platlibdir'] = sys.platlibdir
try:
_CONFIG_VARS['abiflags'] = sys.abiflags
except AttributeError:
# sys.abiflags may not be defined on all platforms.
_CONFIG_VARS['abiflags'] = ''
try:
_CONFIG_VARS['py_version_nodot_plat'] = sys.winver.replace('.', '')
except AttributeError:
_CONFIG_VARS['py_version_nodot_plat'] = ''

if os.name == 'nt':
_init_non_posix(_CONFIG_VARS)
_CONFIG_VARS['VPATH'] = sys._vpath
if os.name == 'posix':
_init_posix(_CONFIG_VARS)
if _HAS_USER_BASE:
# Setting 'userbase' is done below the call to the
# init function to enable using 'get_config_var' in
# the init-function.
_CONFIG_VARS['userbase'] = _getuserbase()

# Always convert srcdir to an absolute path
srcdir = _CONFIG_VARS.get('srcdir', _PROJECT_BASE)
if os.name == 'posix':
if _PYTHON_BUILD:
# If srcdir is a relative path (typically '.' or '..')
# then it should be interpreted relative to the directory
# containing Makefile.
base = os.path.dirname(get_makefile_filename())
srcdir = os.path.join(base, srcdir)
else:
# srcdir is not meaningful since the installation is
# spread about the filesystem. We choose the
# directory containing the Makefile since we know it
# exists.
srcdir = os.path.dirname(get_makefile_filename())
_CONFIG_VARS['srcdir'] = _safe_realpath(srcdir)

# OS X platforms require special customization to handle
# multi-architecture, multi-os-version installers
if sys.platform == 'darwin':
import _osx_support
_osx_support.customize_config_vars(_CONFIG_VARS)

global _CONFIG_VARS_INITIALIZED
_CONFIG_VARS_INITIALIZED = True


def get_config_vars(*args):
"""With no arguments, return a dictionary of all configuration
variables relevant for the current platform.
Expand All @@ -635,66 +705,16 @@ def get_config_vars(*args):
With arguments, return a list of values that result from looking up
each argument in the configuration variable dictionary.
"""
global _CONFIG_VARS
if _CONFIG_VARS is None:
_CONFIG_VARS = {}
# Normalized versions of prefix and exec_prefix are handy to have;
# in fact, these are the standard versions used most places in the
# Distutils.
_CONFIG_VARS['prefix'] = _PREFIX
_CONFIG_VARS['exec_prefix'] = _EXEC_PREFIX
_CONFIG_VARS['py_version'] = _PY_VERSION
_CONFIG_VARS['py_version_short'] = _PY_VERSION_SHORT
_CONFIG_VARS['py_version_nodot'] = _PY_VERSION_SHORT_NO_DOT
_CONFIG_VARS['installed_base'] = _BASE_PREFIX
_CONFIG_VARS['base'] = _PREFIX
_CONFIG_VARS['installed_platbase'] = _BASE_EXEC_PREFIX
_CONFIG_VARS['platbase'] = _EXEC_PREFIX
_CONFIG_VARS['projectbase'] = _PROJECT_BASE
_CONFIG_VARS['platlibdir'] = sys.platlibdir
try:
_CONFIG_VARS['abiflags'] = sys.abiflags
except AttributeError:
# sys.abiflags may not be defined on all platforms.
_CONFIG_VARS['abiflags'] = ''
try:
_CONFIG_VARS['py_version_nodot_plat'] = sys.winver.replace('.', '')
except AttributeError:
_CONFIG_VARS['py_version_nodot_plat'] = ''

if os.name == 'nt':
_init_non_posix(_CONFIG_VARS)
_CONFIG_VARS['VPATH'] = sys._vpath
if os.name == 'posix':
_init_posix(_CONFIG_VARS)
if _HAS_USER_BASE:
# Setting 'userbase' is done below the call to the
# init function to enable using 'get_config_var' in
# the init-function.
_CONFIG_VARS['userbase'] = _getuserbase()

# Always convert srcdir to an absolute path
srcdir = _CONFIG_VARS.get('srcdir', _PROJECT_BASE)
if os.name == 'posix':
if _PYTHON_BUILD:
# If srcdir is a relative path (typically '.' or '..')
# then it should be interpreted relative to the directory
# containing Makefile.
base = os.path.dirname(get_makefile_filename())
srcdir = os.path.join(base, srcdir)
else:
# srcdir is not meaningful since the installation is
# spread about the filesystem. We choose the
# directory containing the Makefile since we know it
# exists.
srcdir = os.path.dirname(get_makefile_filename())
_CONFIG_VARS['srcdir'] = _safe_realpath(srcdir)

# OS X platforms require special customization to handle
# multi-architecture, multi-os-version installers
if sys.platform == 'darwin':
import _osx_support
_osx_support.customize_config_vars(_CONFIG_VARS)

# Avoid claiming the lock once initialization is complete.
if not _CONFIG_VARS_INITIALIZED:
with _CONFIG_VARS_LOCK:
# Test again with the lock held to avoid races. Note that
# we test _CONFIG_VARS here, not _CONFIG_VARS_INITIALIZED,
# to ensure that recursive calls to get_config_vars()
# don't re-enter init_config_vars().
if _CONFIG_VARS is None:
_init_config_vars()
Comment on lines +715 to +717
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The name of the function was changed to _init_config_vars so the comment on line 715 needs to be updated to match.

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This is minor, I think everyone will understand what the comment is saying, but feel free to open a PR updating it.

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I will keep that line in mind for replies to comments on future pull requests.


if args:
vals = []
Expand Down
2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Library/2022-05-08-08-47-32.gh-issue-92452.3pNHe6.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,2 @@
Fixed a race condition that could cause :func:`sysconfig.get_config_var` to
incorrectly return :const:`None` in multi-threaded programs.