[PATCH 4 of 6 import-refactor V3] mercurial: be more strict about loading dual implemented modules
Gregory Szorc
gregory.szorc at gmail.com
Thu Dec 3 23:51:10 CST 2015
# HG changeset patch
# User Gregory Szorc <gregory.szorc at gmail.com>
# Date 1448434204 28800
# Tue Nov 24 22:50:04 2015 -0800
# Node ID 1caabea1ce8e535aee622f3678a92188c461b648
# Parent c5cea2ce781221a791697d0f8c98c24ca083c071
mercurial: be more strict about loading dual implemented modules
With this change in place, we should have slightly stronger guarantees
about how modules with both Python and C implementations are loaded.
Before, our module loader's default policy looked under both mercurial/*
and mercurial/pure/* and imported whatever it found, C or pure. The fact
it looked in both locations by default was a temporary regression from
the beginning of this series.
This patch does 2 things:
1) Changes the default module load policy to only load C modules
2) Verifies that files loaded from mercurial/* are actually C modules
This 2nd behavior change makes our new module loading mechanism
stricter than from before this series. Before, it was possible to load
a .py-based module from mercurial/*. This could happen if an old
installation orphaned a file and then somehow didn't install the C
version for the new install. We now detect this odd configuration
and fall back to loading the pure Python module, assuming it is
allowed. In the case of a busted installation, we fail fast. While
we could fall back, we explicitly decide not to do this because
we don't want people accidentally not running the C modules and having
slow performance as a result.
diff --git a/mercurial/__init__.py b/mercurial/__init__.py
--- a/mercurial/__init__.py
+++ b/mercurial/__init__.py
@@ -17,18 +17,17 @@ import sys
#
# c - require C extensions
# allow - allow pure Python implementation when C loading fails
# py - only load pure Python modules
modulepolicy = '@MODULELOADPOLICY@'
# By default, require the C extensions for performance reasons.
if modulepolicy == '@' 'MODULELOADPOLICY' '@':
- # TODO change to 'c' once installer is changed.
- modulepolicy = 'allow'
+ modulepolicy = 'c'
# Environment variable can always force settings.
modulepolicy = os.environ.get('HGMODULEPOLICY', modulepolicy)
# Modules that have both Python and C implementations. See also the
# set of .py files under mercurial/pure/.
_dualmodules = set([
'mercurial.base85',
@@ -74,21 +73,19 @@ class hgimporter(object):
# for some installations to have .py files under mercurial/*.
# Loading Python modules when we expected C versions could result
# in a) poor performance b) loading a version from a previous
# Mercurial version, potentially leading to incompatibility. Either
# scenario is bad. So we verify that modules loaded from
# mercurial/* are C extensions. If the current policy allows the
# loading of .py modules, the module will be re-imported from
# mercurial/pure/* below.
- # TODO uncomment once setup.py is updated to actually install
- # into mercurial/pure.
- #if modinfo[2][2] != imp.C_EXTENSION:
- # raise ImportError('.py version of %s found where C '
- # 'version should exist' % name)
+ if modinfo[2][2] != imp.C_EXTENSION:
+ raise ImportError('.py version of %s found where C '
+ 'version should exist' % name)
except ImportError:
if modulepolicy == 'c':
raise
# Could not load the C extension and pure Python is allowed. So
# try to load them.
from . import pure
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